How to troubleshoot no start/no fuel/no spark problems
03-01-2011, 09:55 AM
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How to troubleshoot no start/no fuel/no spark problems
Ok, so I may be new to this forum, but I cant help but notice how many no start posts I see. I know most of these problems are easily solved. I work as an honest mechanic, and there is nothing more I hate than to see people do the "process of elimination by swapping parts" method of diagnosis. The other thing I hate is seeing people who have no idea what they are doing try to give advice to someone with a problem.
First off, let me tell you that the tests I will describe will help you diagnose ANY car. Honda, Mitsu, Subi, Yoda, Jag, Mercedes, Lamboughini, Ferrari, McLaren, you name it. They all have the same basic principals. Follow these steps IN ORDER!
Begin by looking at basics. Does the starter turn over? Generally the answer is yes, but if not, the diagnosis is usually very simple.
If you have no crank, begin by testing the starter switch terminal (s terminal) on the starter solenoid. It is always the smallest terminal. All you need to do is have some one crank the engine while you hold a test light on the s terminal. If it lights up, test the positive (+) terminal on the starter solenoid. If should always have power there. If yes, then your problem is the starter/starter solenoid. If the s terminal does not have power when you turn the key on, you must back trace. This requires looking at wiring diagrams unless you know all the sensors in the starting circuit. Most vehicles have just one switch and one sensor. A neutral safety/park neutral switch and the ignition starter switch. Power starts at the battery positive from a 'hot at all times' source in the junction box/fuse box, and travels to the ignition switch. On the ignition switch there are several circuits that split off. Just so I am clear, when I say ignition switch I am talking about the electrical part in the steering columb, not the part your key goes in (lock cylinder). So from the ignition switch power has 3 paths it can run. There is the accessories circuit, the run circuit, and the start circuit. I liike to take the switch out to test it. You must use an ohm meter to do this. If you dont want to take it out you can use a test light to do the same thing. First test the accessories circuit. turn the switch to that position and place the ohm meteron the 'beep' setting and place the leads from the power (+) wire to the accessories wire. MAKE SURE YOU ARE NOT CONNECTED TO POWER! when you are using an voltmeter on ohms setting you need to isolate the circuit completely. It cannot be connected to anything but what you are testing. If you use a test light, turn the key to acc. In both cases you should get a beep or a light. Do the same with all other positions, always going from the power (+) wire to the other circuit wire. If they all test out good move on. If not, you have a bad ignition switch.
Moving on, if they all test good, you go to the next sensor in the circuit. In this thread we will assume the car has no alarm system and the only other sensor is the neutral safety/park safety switch. Move to it. The easiest way to test this is run a jumper wire from the input (+) wire from the ignition switch to the lead that completes the circuit. A nuetral safety switch has just two wires, and you jump those two. A park switch has at least 3 wires, one for input, park, and nuetral. you need to jump from the input (+) wire to the park OR nuetral wire. KEEP IN MIND, this can be dangerous, and the safety switch is there for a reason, and in doing this you are effectively bypassing it. You do this at your own risk!!! After you have jumped the appropriate wires, try to start the car again. If it starts, you have just found the problem. DO NOT, DO NOT, DO NOT keep the nuetral safety switch jumped. This is not safe and it is illegal. Get a new one. They are cheap. If you cant afford the actual switch you can use a push button switch rigged up to work like the nuetral safety switch.
That is the whole test. nothing more to your basic system. Of course some vehicles have extra factors to test such as security systems, and other sensors that must be good for the car to start. For these cars you will need circuit diagrams, but follow the same tests going from sensor to sensor.
Now for the harder to diagnose, cranks but no start:
There are too many variables here, so I am just going to give you starters. If you have further questions you may ask them in a post.
Begin with basic checks again. All gasoline internal combustion engines need the same 4 things to run correctly, assuming the engine is in good 'mechanical' condition. Air, fuel, ignition, and correct timing. Test in that order. Air is something you obviously have, so put it aside for the time being. Test for fuel pressure first. If you do not have a pressure tester, pull off a fuel line by the fuel rail and see if fuel sprays while the engine is being cranked over. If a lot of fuel sprays, you probably have adequite fuel pressure to start the engine at minimum. If fuel is good move on to spark.
Generally, putting a screwdriver in the plug wire is good enough of a test, but not in all cases. Imagine a giant wave of forced air is coming toward you at 1000mph. When it hits you, you are going to get blown back. Well the same thing happens to a spark in an engine. The compression in the engine pushes against the spark, so the spark has to have greater force than the compression to make the jump across the spark plug. If you have a weak coil, it may be able to spark outside the engine with no resistance, but not inside the engine with TONS of resistance. An inline spark tester or an 'air gap' spark tester (simulates compression in the engine) are both fool-proof ways to test spark. If you have spark then check timing.
Start by looking under the timing cover and seeing if the timing belt and cam pulley are turning with the crank. Generally if you see them moving the timing is good, but keep in mind, there could be a dead spot on the timing belt where teeth have fallen off or the belt could have jumped teeth from stretching. In both cases, the timing belt could spin sometimes and not other times, so it is not 100% fool-proof. At this point you have found out you have fuel, you have spark, and you believe you have correct timing. next check compression by renting a compression tester if you do not have one. Check all cylinders. Make sure you disable the fuel pump first. If you have bad compression in either 2 or all cylinders, you need to take the timing cover off and check that the timing marks are on. If they are on, and you still have bad compression the problem is in the engine and is mechanical. It will require taking the cylinder head off at minimum. If the timing marks are off, buy a NEW timing belt AND tensioner, retime it, and you are done. If pistons have slapped the valves you will find this out too without having to take off the cylinder head. Do another compression check after you retime the engine. If you have any cylinders with low compression now it will most likely be due to bent valves.
Now back to fuel. If you do not have good spray out of the fuel line start by testing voltage to the pump. You should get about 3-5v KOEO (key on engine off) and 10-12v KOEC (key on engine cranking), assuming your battery is fully charged and good. If it is not fully charged you may get SLIGHTLY lower numbers. If you get these readings, the pump is bad or something is clogged in the fuel lines. If you do not get these numbers you need to check wiring. It is just like the ignition switch. There is a fuel pump relay or a main relay that powers on the fuel pump. When this relay is activated (eg cranking the engine) the relay should output voltage to the fuel pump. If it does not, it is the problem, or it is the ignition switch itself, not sending power to the relay.
If you had fuel pressure from the beginning, and everything else seemed in proper working order (after you have checked spark, and initial timing) now you need to check injector pulse. The easiest way is with a noid light tester which you can rent for FREE from checker or autozone. If you can get one then use a test light on the injector harness. you should see a flashing light while you crank the engine with either testing method. If you have this, fuel is not your problem. If you do not have this you need to go into electronic sensor diagnosis of the fuel injection system, which takes way to long to explain in typing, but the possible sensors that could have failed are the CKP (crankshaft position sensor) CMP (camshaft position sensor), injector driver (could be in the ecu or its own unit), the ecu itself, or a bad ground to any one of these things. Do keep in mind tho, that some CKP and CMP sensors do not have grounds, as they are variable reluctance sensors and create their own voltage. They only send a signal, nothing more. The other type of sensor is a hall-effect sensor. They use a magnetic field with a disruptor that passes through, interupting the magnetic field. They usually have 3 wires, a reference wire, a signal wire and a ground wire. Some have 2 wires, a reference and signal, and the ground is in the control unit, whatever that may be.
Now for spark diagnosis. If you have no spark with a screwdriver and no spark in the cylinder, start by testing positive voltage to the coil pack. It should see 12v, or battery voltage. If you dont get voltage there, repair the circuit and you are done. If you do get 12v, now test the ignition control module (sometimes this is the ecu itself). The ICM cuts power running through the coil and causes it to induce a spark. Use a test light and test the grounds for the coil. You should get a blinking light while cranking. If you do not, but the coil does have 12v, check power to the ICM. Even if the ICM is in the ECU, there is a power source you can test. This also requires circuit diagrams. If you get power, then the ICM is the problem. If you do get power, you now have to check all the electrical sensors for the ignition circuit. Normally this is just the CKP sensor. The signal wire on the CKP should have a up and down or on and off waveform while cranking, depending on the type of sensor. If it does not fluctuate voltage, the CKP is the culprit.
Now there are hundreds of other factors and problems that can occur, but you find them all the same way. Get a circuit diagram and follow the problem circuit till you find something that is not working like it should. Anyone can do this, you just have to try it. It is really easy and you will suprise yourself at how simple it really is.
If you have additional or more in depth question just ask and I will do my best to explain. Do not PM me, just add a post here.
Thanks
First off, let me tell you that the tests I will describe will help you diagnose ANY car. Honda, Mitsu, Subi, Yoda, Jag, Mercedes, Lamboughini, Ferrari, McLaren, you name it. They all have the same basic principals. Follow these steps IN ORDER!
Begin by looking at basics. Does the starter turn over? Generally the answer is yes, but if not, the diagnosis is usually very simple.
If you have no crank, begin by testing the starter switch terminal (s terminal) on the starter solenoid. It is always the smallest terminal. All you need to do is have some one crank the engine while you hold a test light on the s terminal. If it lights up, test the positive (+) terminal on the starter solenoid. If should always have power there. If yes, then your problem is the starter/starter solenoid. If the s terminal does not have power when you turn the key on, you must back trace. This requires looking at wiring diagrams unless you know all the sensors in the starting circuit. Most vehicles have just one switch and one sensor. A neutral safety/park neutral switch and the ignition starter switch. Power starts at the battery positive from a 'hot at all times' source in the junction box/fuse box, and travels to the ignition switch. On the ignition switch there are several circuits that split off. Just so I am clear, when I say ignition switch I am talking about the electrical part in the steering columb, not the part your key goes in (lock cylinder). So from the ignition switch power has 3 paths it can run. There is the accessories circuit, the run circuit, and the start circuit. I liike to take the switch out to test it. You must use an ohm meter to do this. If you dont want to take it out you can use a test light to do the same thing. First test the accessories circuit. turn the switch to that position and place the ohm meteron the 'beep' setting and place the leads from the power (+) wire to the accessories wire. MAKE SURE YOU ARE NOT CONNECTED TO POWER! when you are using an voltmeter on ohms setting you need to isolate the circuit completely. It cannot be connected to anything but what you are testing. If you use a test light, turn the key to acc. In both cases you should get a beep or a light. Do the same with all other positions, always going from the power (+) wire to the other circuit wire. If they all test out good move on. If not, you have a bad ignition switch.
Moving on, if they all test good, you go to the next sensor in the circuit. In this thread we will assume the car has no alarm system and the only other sensor is the neutral safety/park safety switch. Move to it. The easiest way to test this is run a jumper wire from the input (+) wire from the ignition switch to the lead that completes the circuit. A nuetral safety switch has just two wires, and you jump those two. A park switch has at least 3 wires, one for input, park, and nuetral. you need to jump from the input (+) wire to the park OR nuetral wire. KEEP IN MIND, this can be dangerous, and the safety switch is there for a reason, and in doing this you are effectively bypassing it. You do this at your own risk!!! After you have jumped the appropriate wires, try to start the car again. If it starts, you have just found the problem. DO NOT, DO NOT, DO NOT keep the nuetral safety switch jumped. This is not safe and it is illegal. Get a new one. They are cheap. If you cant afford the actual switch you can use a push button switch rigged up to work like the nuetral safety switch.
That is the whole test. nothing more to your basic system. Of course some vehicles have extra factors to test such as security systems, and other sensors that must be good for the car to start. For these cars you will need circuit diagrams, but follow the same tests going from sensor to sensor.
Now for the harder to diagnose, cranks but no start:
There are too many variables here, so I am just going to give you starters. If you have further questions you may ask them in a post.
Begin with basic checks again. All gasoline internal combustion engines need the same 4 things to run correctly, assuming the engine is in good 'mechanical' condition. Air, fuel, ignition, and correct timing. Test in that order. Air is something you obviously have, so put it aside for the time being. Test for fuel pressure first. If you do not have a pressure tester, pull off a fuel line by the fuel rail and see if fuel sprays while the engine is being cranked over. If a lot of fuel sprays, you probably have adequite fuel pressure to start the engine at minimum. If fuel is good move on to spark.
Generally, putting a screwdriver in the plug wire is good enough of a test, but not in all cases. Imagine a giant wave of forced air is coming toward you at 1000mph. When it hits you, you are going to get blown back. Well the same thing happens to a spark in an engine. The compression in the engine pushes against the spark, so the spark has to have greater force than the compression to make the jump across the spark plug. If you have a weak coil, it may be able to spark outside the engine with no resistance, but not inside the engine with TONS of resistance. An inline spark tester or an 'air gap' spark tester (simulates compression in the engine) are both fool-proof ways to test spark. If you have spark then check timing.
Start by looking under the timing cover and seeing if the timing belt and cam pulley are turning with the crank. Generally if you see them moving the timing is good, but keep in mind, there could be a dead spot on the timing belt where teeth have fallen off or the belt could have jumped teeth from stretching. In both cases, the timing belt could spin sometimes and not other times, so it is not 100% fool-proof. At this point you have found out you have fuel, you have spark, and you believe you have correct timing. next check compression by renting a compression tester if you do not have one. Check all cylinders. Make sure you disable the fuel pump first. If you have bad compression in either 2 or all cylinders, you need to take the timing cover off and check that the timing marks are on. If they are on, and you still have bad compression the problem is in the engine and is mechanical. It will require taking the cylinder head off at minimum. If the timing marks are off, buy a NEW timing belt AND tensioner, retime it, and you are done. If pistons have slapped the valves you will find this out too without having to take off the cylinder head. Do another compression check after you retime the engine. If you have any cylinders with low compression now it will most likely be due to bent valves.
Now back to fuel. If you do not have good spray out of the fuel line start by testing voltage to the pump. You should get about 3-5v KOEO (key on engine off) and 10-12v KOEC (key on engine cranking), assuming your battery is fully charged and good. If it is not fully charged you may get SLIGHTLY lower numbers. If you get these readings, the pump is bad or something is clogged in the fuel lines. If you do not get these numbers you need to check wiring. It is just like the ignition switch. There is a fuel pump relay or a main relay that powers on the fuel pump. When this relay is activated (eg cranking the engine) the relay should output voltage to the fuel pump. If it does not, it is the problem, or it is the ignition switch itself, not sending power to the relay.
If you had fuel pressure from the beginning, and everything else seemed in proper working order (after you have checked spark, and initial timing) now you need to check injector pulse. The easiest way is with a noid light tester which you can rent for FREE from checker or autozone. If you can get one then use a test light on the injector harness. you should see a flashing light while you crank the engine with either testing method. If you have this, fuel is not your problem. If you do not have this you need to go into electronic sensor diagnosis of the fuel injection system, which takes way to long to explain in typing, but the possible sensors that could have failed are the CKP (crankshaft position sensor) CMP (camshaft position sensor), injector driver (could be in the ecu or its own unit), the ecu itself, or a bad ground to any one of these things. Do keep in mind tho, that some CKP and CMP sensors do not have grounds, as they are variable reluctance sensors and create their own voltage. They only send a signal, nothing more. The other type of sensor is a hall-effect sensor. They use a magnetic field with a disruptor that passes through, interupting the magnetic field. They usually have 3 wires, a reference wire, a signal wire and a ground wire. Some have 2 wires, a reference and signal, and the ground is in the control unit, whatever that may be.
Now for spark diagnosis. If you have no spark with a screwdriver and no spark in the cylinder, start by testing positive voltage to the coil pack. It should see 12v, or battery voltage. If you dont get voltage there, repair the circuit and you are done. If you do get 12v, now test the ignition control module (sometimes this is the ecu itself). The ICM cuts power running through the coil and causes it to induce a spark. Use a test light and test the grounds for the coil. You should get a blinking light while cranking. If you do not, but the coil does have 12v, check power to the ICM. Even if the ICM is in the ECU, there is a power source you can test. This also requires circuit diagrams. If you get power, then the ICM is the problem. If you do get power, you now have to check all the electrical sensors for the ignition circuit. Normally this is just the CKP sensor. The signal wire on the CKP should have a up and down or on and off waveform while cranking, depending on the type of sensor. If it does not fluctuate voltage, the CKP is the culprit.
Now there are hundreds of other factors and problems that can occur, but you find them all the same way. Get a circuit diagram and follow the problem circuit till you find something that is not working like it should. Anyone can do this, you just have to try it. It is really easy and you will suprise yourself at how simple it really is.
If you have additional or more in depth question just ask and I will do my best to explain. Do not PM me, just add a post here.
Thanks
03-05-2011, 02:55 PM
#5
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Re: How to troubleshoot no start/no fuel/no spark problems
alright. ive got one for you. i completed a JDM b20b swap into my 89 hatch recently, and it will turn over but it wont start because the injectors are not firing(no fuel spray if i take out a sparkplug and look down the tube as someone cranks it. and a noid lite didnt light up ever)). it has fuel to the injectors. it has spark. it has timing. it has been converted to obd1.
-i did the dpfi->mpfi first and ive checked my wiring. its all seems to be right.
-i purchased an obd0->obd1 conversion harness and it is plugged in.
-i had a junkyard obd1 ECU in it, but replaced it today with a refurbished and chipped obd1 ECU.
-i picked up several spare main relays from the junk yard and i have one that is functioning properly in the car now.
-the #14fuse(ecu and efi) is fine.
-i worked out a grounding issue as well, so its grounded properly now.
-the dizzy's cap was crushed and the wiring was chopped when the engine arrived from japan. so i have replaced teh cap and the rotor. and i repinned the obd2 dizzy's clip so i could plug it directly into the obd0 engine harness.(matched the colors from 0bd0 to obd1 to obd2. was a pain)
-it has about 4 gallons of 89 octane in it.
-the fuel pump IS priming and working.
-i am getting voltage to the injectors.
-im using the b20b's obd2 injectors, but ive been told they will work fine as long as i have it converted to obd1(which i have).
-im using the b20b's obd2 dizzy, but again, ive been told that if its converted to obd1 that it will work just fine.
-i am getting the proper voltage to the TPS(4.7v with the ignition on, if i remember correctly)
SO, something is stopping all 4 of the injectors from firing. im thinking that its the crankshaft position sensor or the camshaft position sensor inside the dizzy. how should i test to see if one of those is bad? and which one of those controls when the injectors will fire on this engine?
-i did the dpfi->mpfi first and ive checked my wiring. its all seems to be right.
-i purchased an obd0->obd1 conversion harness and it is plugged in.
-i had a junkyard obd1 ECU in it, but replaced it today with a refurbished and chipped obd1 ECU.
-i picked up several spare main relays from the junk yard and i have one that is functioning properly in the car now.
-the #14fuse(ecu and efi) is fine.
-i worked out a grounding issue as well, so its grounded properly now.
-the dizzy's cap was crushed and the wiring was chopped when the engine arrived from japan. so i have replaced teh cap and the rotor. and i repinned the obd2 dizzy's clip so i could plug it directly into the obd0 engine harness.(matched the colors from 0bd0 to obd1 to obd2. was a pain)
-it has about 4 gallons of 89 octane in it.
-the fuel pump IS priming and working.
-i am getting voltage to the injectors.
-im using the b20b's obd2 injectors, but ive been told they will work fine as long as i have it converted to obd1(which i have).
-im using the b20b's obd2 dizzy, but again, ive been told that if its converted to obd1 that it will work just fine.
-i am getting the proper voltage to the TPS(4.7v with the ignition on, if i remember correctly)
SO, something is stopping all 4 of the injectors from firing. im thinking that its the crankshaft position sensor or the camshaft position sensor inside the dizzy. how should i test to see if one of those is bad? and which one of those controls when the injectors will fire on this engine?
03-07-2011, 06:56 PM
#6
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Re: How to troubleshoot no start/no fuel/no spark problems
Yes my friend has an 89 crx si, it will crank but wont start. we can push start it and it runs perfect just wont fire up when cranking... any ideas?
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11-11-2014, 03:11 PM
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Re: How to troubleshoot no start/no fuel/no spark problems
Okay i bought my lude non running i pulled the engine rebuilt it and its back in now all wires are hooked up correctly. When cranking i did the screwdriver test and got no spark. I then checked the coil by spec and its fine and the igniter and its in spec. I then traces wires back to the ecu and they all have continuity. Im still getting no spark i am manually by passing the ignition system by jumping the starter with jumper wire and push button. No spark. I am lost as to what it can be ive tested like everything would it be my ecu then?
03-08-2016, 01:33 AM
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Re: How to troubleshoot no start/no fuel/no spark problems
hey man . could oil all under starter , oil corrosion on battery wires , washers between screws onto silineod and power shorting some where oil bad connection somewhwere doing this . im gona clean all around. cables cleaned . getting rid of broken washers. . then ill tryto crank . got new battery and now seems battery lost abbity to stay charged. think maybe messing ny battery up. so ima clean hook it up , any suggestions. maybe neutrsl switch(near tranny? ithink) oiled ****ed up stuck in wrong gear. and switch under shifter (i broke that plastic thing. maybe ok withoutfriend said.gona check them 3 circuit wires from starter. im sure there all sticky and ill try to test ...200,000miles but nice. someone said multiplex... conputer thing srs. security theft cpu thing maybe. my check engine had been on for few months. and buddy hooked up code readr to it and came back some kinda transmission control system failure... any thing simple i can check and maybe get luky if so hook me up ... but thanks for some info. ill start small ,.. phuk that multiplex talk right... nott likely??
04-12-2016, 03:02 AM
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Re: How to troubleshoot no start/no fuel/no spark problems
Ok, so I may be new to this forum, but I cant help but notice how many no start posts I see. I know most of these problems are easily solved. I work as an honest mechanic, and there is nothing more I hate than to see people do the "process of elimination by swapping parts" method of diagnosis. The other thing I hate is seeing people who have no idea what they are doing try to give advice to someone with a problem.
First off, let me tell you that the tests I will describe will help you diagnose ANY car. Honda, Mitsu, Subi, Yoda, Jag, Mercedes, Lamboughini, Ferrari, McLaren, you name it. They all have the same basic principals. Follow these steps IN ORDER!
Begin by looking at basics. Does the starter turn over? Generally the answer is yes, but if not, the diagnosis is usually very simple.
If you have no crank, begin by testing the starter switch terminal (s terminal) on the starter solenoid. It is always the smallest terminal. All you need to do is have some one crank the engine while you hold a test light on the s terminal. If it lights up, test the positive (+) terminal on the starter solenoid. If should always have power there. If yes, then your problem is the starter/starter solenoid. If the s terminal does not have power when you turn the key on, you must back trace. This requires looking at wiring diagrams unless you know all the sensors in the starting circuit. Most vehicles have just one switch and one sensor. A neutral safety/park neutral switch and the ignition starter switch. Power starts at the battery positive from a 'hot at all times' source in the junction box/fuse box, and travels to the ignition switch. On the ignition switch there are several circuits that split off. Just so I am clear, when I say ignition switch I am talking about the electrical part in the steering columb, not the part your key goes in (lock cylinder). So from the ignition switch power has 3 paths it can run. There is the accessories circuit, the run circuit, and the start circuit. I liike to take the switch out to test it. You must use an ohm meter to do this. If you dont want to take it out you can use a test light to do the same thing. First test the accessories circuit. turn the switch to that position and place the ohm meteron the 'beep' setting and place the leads from the power (+) wire to the accessories wire. MAKE SURE YOU ARE NOT CONNECTED TO POWER! when you are using an voltmeter on ohms setting you need to isolate the circuit completely. It cannot be connected to anything but what you are testing. If you use a test light, turn the key to acc. In both cases you should get a beep or a light. Do the same with all other positions, always going from the power (+) wire to the other circuit wire. If they all test out good move on. If not, you have a bad ignition switch.
Moving on, if they all test good, you go to the next sensor in the circuit. In this thread we will assume the car has no alarm system and the only other sensor is the neutral safety/park safety switch. Move to it. The easiest way to test this is run a jumper wire from the input (+) wire from the ignition switch to the lead that completes the circuit. A nuetral safety switch has just two wires, and you jump those two. A park switch has at least 3 wires, one for input, park, and nuetral. you need to jump from the input (+) wire to the park OR nuetral wire. KEEP IN MIND, this can be dangerous, and the safety switch is there for a reason, and in doing this you are effectively bypassing it. You do this at your own risk!!! After you have jumped the appropriate wires, try to start the car again. If it starts, you have just found the problem. DO NOT, DO NOT, DO NOT keep the nuetral safety switch jumped. This is not safe and it is illegal. Get a new one. They are cheap. If you cant afford the actual switch you can use a push button switch rigged up to work like the nuetral safety switch.
That is the whole test. nothing more to your basic system. Of course some vehicles have extra factors to test such as security systems, and other sensors that must be good for the car to start. For these cars you will need circuit diagrams, but follow the same tests going from sensor to sensor.
Now for the harder to diagnose, cranks but no start:
There are too many variables here, so I am just going to give you starters. If you have further questions you may ask them in a post.
Begin with basic checks again. All gasoline internal combustion engines need the same 4 things to run correctly, assuming the engine is in good 'mechanical' condition. Air, fuel, ignition, and correct timing. Test in that order. Air is something you obviously have, so put it aside for the time being. Test for fuel pressure first. If you do not have a pressure tester, pull off a fuel line by the fuel rail and see if fuel sprays while the engine is being cranked over. If a lot of fuel sprays, you probably have adequite fuel pressure to start the engine at minimum. If fuel is good move on to spark.
Generally, putting a screwdriver in the plug wire is good enough of a test, but not in all cases. Imagine a giant wave of forced air is coming toward you at 1000mph. When it hits you, you are going to get blown back. Well the same thing happens to a spark in an engine. The compression in the engine pushes against the spark, so the spark has to have greater force than the compression to make the jump across the spark plug. If you have a weak coil, it may be able to spark outside the engine with no resistance, but not inside the engine with TONS of resistance. An inline spark tester or an 'air gap' spark tester (simulates compression in the engine) are both fool-proof ways to test spark. If you have spark then check timing.
Start by looking under the timing cover and seeing if the timing belt and cam pulley are turning with the crank. Generally if you see them moving the timing is good, but keep in mind, there could be a dead spot on the timing belt where teeth have fallen off or the belt could have jumped teeth from stretching. In both cases, the timing belt could spin sometimes and not other times, so it is not 100% fool-proof. At this point you have found out you have fuel, you have spark, and you believe you have correct timing. next check compression by renting a compression tester if you do not have one. Check all cylinders. Make sure you disable the fuel pump first. If you have bad compression in either 2 or all cylinders, you need to take the timing cover off and check that the timing marks are on. If they are on, and you still have bad compression the problem is in the engine and is mechanical. It will require taking the cylinder head off at minimum. If the timing marks are off, buy a NEW timing belt AND tensioner, retime it, and you are done. If pistons have slapped the valves you will find this out too without having to take off the cylinder head. Do another compression check after you retime the engine. If you have any cylinders with low compression now it will most likely be due to bent valves.
Now back to fuel. If you do not have good spray out of the fuel line start by testing voltage to the pump. You should get about 3-5v KOEO (key on engine off) and 10-12v KOEC (key on engine cranking), assuming your battery is fully charged and good. If it is not fully charged you may get SLIGHTLY lower numbers. If you get these readings, the pump is bad or something is clogged in the fuel lines. If you do not get these numbers you need to check wiring. It is just like the ignition switch. There is a fuel pump relay or a main relay that powers on the fuel pump. When this relay is activated (eg cranking the engine) the relay should output voltage to the fuel pump. If it does not, it is the problem, or it is the ignition switch itself, not sending power to the relay.
If you had fuel pressure from the beginning, and everything else seemed in proper working order (after you have checked spark, and initial timing) now you need to check injector pulse. The easiest way is with a noid light tester which you can rent for FREE from checker or autozone. If you can get one then use a test light on the injector harness. you should see a flashing light while you crank the engine with either testing method. If you have this, fuel is not your problem. If you do not have this you need to go into electronic sensor diagnosis of the fuel injection system, which takes way to long to explain in typing, but the possible sensors that could have failed are the CKP (crankshaft position sensor) CMP (camshaft position sensor), injector driver (could be in the ecu or its own unit), the ecu itself, or a bad ground to any one of these things. Do keep in mind tho, that some CKP and CMP sensors do not have grounds, as they are variable reluctance sensors and create their own voltage. They only send a signal, nothing more. The other type of sensor is a hall-effect sensor. They use a magnetic field with a disruptor that passes through, interupting the magnetic field. They usually have 3 wires, a reference wire, a signal wire and a ground wire. Some have 2 wires, a reference and signal, and the ground is in the control unit, whatever that may be.
Now for spark diagnosis. If you have no spark with a screwdriver and no spark in the cylinder, start by testing positive voltage to the coil pack. It should see 12v, or battery voltage. If you dont get voltage there, repair the circuit and you are done. If you do get 12v, now test the ignition control module (sometimes this is the ecu itself). The ICM cuts power running through the coil and causes it to induce a spark. Use a test light and test the grounds for the coil. You should get a blinking light while cranking. If you do not, but the coil does have 12v, check power to the ICM. Even if the ICM is in the ECU, there is a power source you can test. This also requires circuit diagrams. If you get power, then the ICM is the problem. If you do get power, you now have to check all the electrical sensors for the ignition circuit. Normally this is just the CKP sensor. The signal wire on the CKP should have a up and down or on and off waveform while cranking, depending on the type of sensor. If it does not fluctuate voltage, the CKP is the culprit.
Now there are hundreds of other factors and problems that can occur, but you find them all the same way. Get a circuit diagram and follow the problem circuit till you find something that is not working like it should. Anyone can do this, you just have to try it. It is really easy and you will suprise yourself at how simple it really is.
If you have additional or more in depth question just ask and I will do my best to explain. Do not PM me, just add a post here.
Thanks
First off, let me tell you that the tests I will describe will help you diagnose ANY car. Honda, Mitsu, Subi, Yoda, Jag, Mercedes, Lamboughini, Ferrari, McLaren, you name it. They all have the same basic principals. Follow these steps IN ORDER!
Begin by looking at basics. Does the starter turn over? Generally the answer is yes, but if not, the diagnosis is usually very simple.
If you have no crank, begin by testing the starter switch terminal (s terminal) on the starter solenoid. It is always the smallest terminal. All you need to do is have some one crank the engine while you hold a test light on the s terminal. If it lights up, test the positive (+) terminal on the starter solenoid. If should always have power there. If yes, then your problem is the starter/starter solenoid. If the s terminal does not have power when you turn the key on, you must back trace. This requires looking at wiring diagrams unless you know all the sensors in the starting circuit. Most vehicles have just one switch and one sensor. A neutral safety/park neutral switch and the ignition starter switch. Power starts at the battery positive from a 'hot at all times' source in the junction box/fuse box, and travels to the ignition switch. On the ignition switch there are several circuits that split off. Just so I am clear, when I say ignition switch I am talking about the electrical part in the steering columb, not the part your key goes in (lock cylinder). So from the ignition switch power has 3 paths it can run. There is the accessories circuit, the run circuit, and the start circuit. I liike to take the switch out to test it. You must use an ohm meter to do this. If you dont want to take it out you can use a test light to do the same thing. First test the accessories circuit. turn the switch to that position and place the ohm meteron the 'beep' setting and place the leads from the power (+) wire to the accessories wire. MAKE SURE YOU ARE NOT CONNECTED TO POWER! when you are using an voltmeter on ohms setting you need to isolate the circuit completely. It cannot be connected to anything but what you are testing. If you use a test light, turn the key to acc. In both cases you should get a beep or a light. Do the same with all other positions, always going from the power (+) wire to the other circuit wire. If they all test out good move on. If not, you have a bad ignition switch.
Moving on, if they all test good, you go to the next sensor in the circuit. In this thread we will assume the car has no alarm system and the only other sensor is the neutral safety/park safety switch. Move to it. The easiest way to test this is run a jumper wire from the input (+) wire from the ignition switch to the lead that completes the circuit. A nuetral safety switch has just two wires, and you jump those two. A park switch has at least 3 wires, one for input, park, and nuetral. you need to jump from the input (+) wire to the park OR nuetral wire. KEEP IN MIND, this can be dangerous, and the safety switch is there for a reason, and in doing this you are effectively bypassing it. You do this at your own risk!!! After you have jumped the appropriate wires, try to start the car again. If it starts, you have just found the problem. DO NOT, DO NOT, DO NOT keep the nuetral safety switch jumped. This is not safe and it is illegal. Get a new one. They are cheap. If you cant afford the actual switch you can use a push button switch rigged up to work like the nuetral safety switch.
That is the whole test. nothing more to your basic system. Of course some vehicles have extra factors to test such as security systems, and other sensors that must be good for the car to start. For these cars you will need circuit diagrams, but follow the same tests going from sensor to sensor.
Now for the harder to diagnose, cranks but no start:
There are too many variables here, so I am just going to give you starters. If you have further questions you may ask them in a post.
Begin with basic checks again. All gasoline internal combustion engines need the same 4 things to run correctly, assuming the engine is in good 'mechanical' condition. Air, fuel, ignition, and correct timing. Test in that order. Air is something you obviously have, so put it aside for the time being. Test for fuel pressure first. If you do not have a pressure tester, pull off a fuel line by the fuel rail and see if fuel sprays while the engine is being cranked over. If a lot of fuel sprays, you probably have adequite fuel pressure to start the engine at minimum. If fuel is good move on to spark.
Generally, putting a screwdriver in the plug wire is good enough of a test, but not in all cases. Imagine a giant wave of forced air is coming toward you at 1000mph. When it hits you, you are going to get blown back. Well the same thing happens to a spark in an engine. The compression in the engine pushes against the spark, so the spark has to have greater force than the compression to make the jump across the spark plug. If you have a weak coil, it may be able to spark outside the engine with no resistance, but not inside the engine with TONS of resistance. An inline spark tester or an 'air gap' spark tester (simulates compression in the engine) are both fool-proof ways to test spark. If you have spark then check timing.
Start by looking under the timing cover and seeing if the timing belt and cam pulley are turning with the crank. Generally if you see them moving the timing is good, but keep in mind, there could be a dead spot on the timing belt where teeth have fallen off or the belt could have jumped teeth from stretching. In both cases, the timing belt could spin sometimes and not other times, so it is not 100% fool-proof. At this point you have found out you have fuel, you have spark, and you believe you have correct timing. next check compression by renting a compression tester if you do not have one. Check all cylinders. Make sure you disable the fuel pump first. If you have bad compression in either 2 or all cylinders, you need to take the timing cover off and check that the timing marks are on. If they are on, and you still have bad compression the problem is in the engine and is mechanical. It will require taking the cylinder head off at minimum. If the timing marks are off, buy a NEW timing belt AND tensioner, retime it, and you are done. If pistons have slapped the valves you will find this out too without having to take off the cylinder head. Do another compression check after you retime the engine. If you have any cylinders with low compression now it will most likely be due to bent valves.
Now back to fuel. If you do not have good spray out of the fuel line start by testing voltage to the pump. You should get about 3-5v KOEO (key on engine off) and 10-12v KOEC (key on engine cranking), assuming your battery is fully charged and good. If it is not fully charged you may get SLIGHTLY lower numbers. If you get these readings, the pump is bad or something is clogged in the fuel lines. If you do not get these numbers you need to check wiring. It is just like the ignition switch. There is a fuel pump relay or a main relay that powers on the fuel pump. When this relay is activated (eg cranking the engine) the relay should output voltage to the fuel pump. If it does not, it is the problem, or it is the ignition switch itself, not sending power to the relay.
If you had fuel pressure from the beginning, and everything else seemed in proper working order (after you have checked spark, and initial timing) now you need to check injector pulse. The easiest way is with a noid light tester which you can rent for FREE from checker or autozone. If you can get one then use a test light on the injector harness. you should see a flashing light while you crank the engine with either testing method. If you have this, fuel is not your problem. If you do not have this you need to go into electronic sensor diagnosis of the fuel injection system, which takes way to long to explain in typing, but the possible sensors that could have failed are the CKP (crankshaft position sensor) CMP (camshaft position sensor), injector driver (could be in the ecu or its own unit), the ecu itself, or a bad ground to any one of these things. Do keep in mind tho, that some CKP and CMP sensors do not have grounds, as they are variable reluctance sensors and create their own voltage. They only send a signal, nothing more. The other type of sensor is a hall-effect sensor. They use a magnetic field with a disruptor that passes through, interupting the magnetic field. They usually have 3 wires, a reference wire, a signal wire and a ground wire. Some have 2 wires, a reference and signal, and the ground is in the control unit, whatever that may be.
Now for spark diagnosis. If you have no spark with a screwdriver and no spark in the cylinder, start by testing positive voltage to the coil pack. It should see 12v, or battery voltage. If you dont get voltage there, repair the circuit and you are done. If you do get 12v, now test the ignition control module (sometimes this is the ecu itself). The ICM cuts power running through the coil and causes it to induce a spark. Use a test light and test the grounds for the coil. You should get a blinking light while cranking. If you do not, but the coil does have 12v, check power to the ICM. Even if the ICM is in the ECU, there is a power source you can test. This also requires circuit diagrams. If you get power, then the ICM is the problem. If you do get power, you now have to check all the electrical sensors for the ignition circuit. Normally this is just the CKP sensor. The signal wire on the CKP should have a up and down or on and off waveform while cranking, depending on the type of sensor. If it does not fluctuate voltage, the CKP is the culprit.
Now there are hundreds of other factors and problems that can occur, but you find them all the same way. Get a circuit diagram and follow the problem circuit till you find something that is not working like it should. Anyone can do this, you just have to try it. It is really easy and you will suprise yourself at how simple it really is.
If you have additional or more in depth question just ask and I will do my best to explain. Do not PM me, just add a post here.
Thanks
07-04-2016, 09:41 AM
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Re: How to troubleshoot no start/no fuel/no spark problems
Hi I have a 85 Ford f150 efi 5.0 it will crank but won't start or run unless we continually sqiurt directly down the intake. Hooked injectors directly to batterty and they didn't click. We then used a tester light to test the power to the plug. When the key was on there was power to both prongs of the plug. When cranked there was still power to both but the black wire did pulse a little bit. Do I have bad injectors or is there also an electrical problem?
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