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Old 06-28-2011, 04:18 PM   #1
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Default 93 civic fuel pump problem..

hey guys
so last night i was trying to start my car and the fuel pump was working fine for a little bit. After trying to start it for a little bit the fuel pump just stopped working. So i thought the main fuse was bad so i bought a new one. I replaced the Relay and still the fuel pump will not prime. So i went out today bought a new fuel pump and installed it, even with the new relay and pump i still do not here the pump priming.. Any Ideas?
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Old 06-28-2011, 05:37 PM   #2
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Default Re: 93 civic fuel pump problem..

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Originally Posted by Jay_Mills View Post
hey guys
so last night i was trying to start my car and the fuel pump was working fine for a little bit. After trying to start it for a little bit the fuel pump just stopped working. So i thought the main fuse was bad so i bought a new one. I replaced the Relay and still the fuel pump will not prime. So i went out today bought a new fuel pump and installed it, even with the new relay and pump i still do not here the pump priming.. Any Ideas?
that problem shows up in my car once in a while, let me know what you did when u get it fixed.

mine wont prime sometimes, or it will start but immediately die out. I'm starting to guess that my ECU is starting to fail.
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Old 06-28-2011, 10:01 PM   #3
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Default Re: 93 civic fuel pump problem..

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Originally Posted by mibayaua View Post
that problem shows up in my car once in a while, let me know what you did when u get it fixed.

mine wont prime sometimes, or it will start but immediately die out. I'm starting to guess that my ECU is starting to fail.
fur sure bro.. im starting to think its my ecu also.. either that or some were in my harness there is a faulty wire.. idk.. but i am doin a swap into my car soo all problems are starting to show up rite now.. Murphy's law in effect to the fullest ..
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Old 06-29-2011, 01:31 AM   #4
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Default Re: 93 civic fuel pump problem..

I had a friend who had this problem - spent many months trying to figure it out and yes, when he swapped his ecu the problem went away for good. I am guessing the ecu might have dry soldering joints or something from moisture, etc....
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Old 06-29-2011, 06:47 AM   #5
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Default Re: 93 civic fuel pump problem..

try a different ecu i did and that was the problem

now why my ecu went bad i dunno
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Old 06-29-2011, 07:37 AM   #6
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Default Re: 93 civic fuel pump problem..

It was probably dry joints in the soldering of the ecu or components that just went bad in the ecu. Moisture is the common cause of this in all types of other electronics too but not so much nowdays since soldering technology has come a long way.
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Old 06-29-2011, 10:33 AM   #7
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Default Re: 93 civic fuel pump problem..

thnk you guys for all of the replays.. But last night as i was trying to fix this problem once again i had takin my friends ecu outta his teg since i have the b series motor and the pump still does not work and i also tried to see if the 5 n 7 plugs were getting power and they are getting power fur sure.. So im goin to try and get a new main fuse a brand new one and see what happens then.. Also im thinking about getting a new harness for the interior or tracing the fuel pump wires n replacing them.. But if all else fails then imma have to take it to a Mechanic and mechanics are never good..
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Old 06-29-2011, 10:50 AM   #8
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Default Re: 93 civic fuel pump problem..

I had this same problem with my 93 del sol si automatic. It was a wet ECU. I don't know if the del sol's have water leaks that soak the ecu but I swapped in a P28 for a manual car and the fuel pump primed and the car started right up. I'm waiting for another P28-A51 to come in. I tried another P28 from a 92 civic it wasn't a A-51 but it didn't work for some reason. Maybe it was a A02?But in chasing my starting problem I tried the main relay, the PGM-FI relay, the thermostat housing ground wires, the fuel pump and the ignition switch.
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Old 06-29-2011, 11:29 AM   #9
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Default Re: 93 civic fuel pump problem..

Quote:
Originally Posted by delsolintegra View Post
I had this same problem with my 93 del sol si automatic. It was a wet ECU. I don't know if the del sol's have water leaks that soak the ecu but I swapped in a P28 for a manual car and the fuel pump primed and the car started right up. I'm waiting for another P28-A51 to come in. I tried another P28 from a 92 civic it wasn't a A-51 but it didn't work for some reason. Maybe it was a A02?But in chasing my starting problem I tried the main relay, the PGM-FI relay, the thermostat housing ground wires, the fuel pump and the ignition switch.
the t-stat ground wires seem like another good place to start i havent checked those yet. and as far as the ignition switch and the ecu imma go buy another set of those.. and then we will see what happens if the car doesnt wanna run after then its time to say buy buy to it part it out and go get another coupe or a hatchy.. im hoping i dnt have to do that though..
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Old 06-29-2011, 07:32 PM   #10
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Default Re: 93 civic fuel pump problem..

The fuel pump is controlled by the PGM-FI Main Relay, which in turn is controlled by the ign. switch and the ECU/ECM, the PGM-FI Main Relay is powered by 3 fuses, sorry do not have a wire guide for a 93 Civic.

However, i would start by dropping the PGM-FI Main Relay and testing for the 3 powers at the relay plug, there needs to be a 12V constant, [hot at all times] a 12V switched, [hot in run and start] and a 2nd 12V switched, [hot during cranking to start only].

Make sure you have all 3 and they are hot when they are supposed to be, [ign. key positions].
Mark down the colors of the leads and which power they are.

If powers are good, test the ground, [black] needs to be full continuity to chassis ground.

That will make four of the seven leads on the plug, two of the others are 12V+ outputs, [fuel injector relay output and fuel pump relay output] the third one is the ECU control lead input for the fuel pump relay , it is a "low current" ground.

The next test is to plug the relay in and find the fuel injector relay output lead, it will be 12V+ when ign. key is turned to run, [or start], the fuel pump relays output lead is most likely a yellow/green, [the fuel injector relays output lead may also be yellow/green, but it may not be, so it needs to be found and marked, that will leave you with one lead, [ECU fuel pump relay control lead.

If everything else is working except fuel pump lead, [no power on yellow/green] use a jumper lead and supply a ground to the lead you have determined to be the ECU control lead , it may be a green/blue or a green/yellow, maybe a green/black, if grounding that lead turns on the fuel pump, you will need to check IPG1 and IPG2 inputs on the ECU/ECM, they will be the same color as the fuel injector output lead and must have 12V+ on them when ign. is on or there will be no fuel pump relay control output from ECU/ECM. 94
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Old 06-29-2011, 08:10 PM   #11
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Default Re: 93 civic fuel pump problem..

Okay guys.. soo im super excited i found out the problem just like 5 seconds ago i looked at the T-stat ground and the wire for it was shower wires thew the covering the wires kept touching other things i rapped some tape around them and Walaa the problem was fixed.. i cnt believe i didnt check that in the first place.. but whatev its fixed now..
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Old 08-02-2011, 10:57 PM   #12
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Default Re: 93 civic fuel pump problem..

Thanks, fcm.

Re-Soldering the Main Relay fixed a similar problem on my son's 1992 Honda Civic DX. The common thread to the times it would not start was that the interior was hot (car in sun, in Summer). This began late last Summer, we replaced the fuel pump, and it seemed fixed. Then this summer it sometimes wouldn't start in the afternoons, worked fine by night and in the morning. Sometimes, opening the door for a while got it working again. Of course, depending on the way the solder joint fails, temperature might have nothing to do with this on some other vehicles.

For a good picture showing how to find the bad solder joints, see Circuit Star-29's first post in thread ?? 97 Civic - ODD NO START SOMETIMES - no spark or fuel?? . This thread has other posts with instructions on re-soldering the relay, and some similar problems that also could be causes.

You could also just replace the relay unit, if $100 is cheaper than your time to re-solder it, or you suspect the contacts are bad. Haynes has a procedure for checking the relay, but it passed those tests every time. The location of the relay probably contributes to it staying hot; removing it to test let it cool and seem OK.

The pins for the 92 are marked on the relay, and my wiring diagram identifies them as follows:
1 - Always +12V (from ELD)
2 - Ground
3 - Fuel Injector Output
5 - +12V Run and Start (from ELD)
6 - +12V During Start only (from Ignition Sw via interlocks)
7 - Fuel Pump Output
8 - ECU Fuel Pump Signal FLR1 & FLR2
(IGP1 and IGP2 are grounds connected to the Main Relay Ground in the same harness, according to my diagram, for a 1993 Civic in the Haynes manual).

The Main Relay switches power for the Fuel Injector System and Fuel Pump from Battery, via the Electronic Load Detector (ELD). The injector system (and a few other devices) get +12V from this relay whenever the Ignition Switch is on (including Start). This also powers the second relay, through a resistor and diode, when the ECU signals the fuel pump by grounding the other end of the relay coil. The start power input apparently assures the second relay stays on despite reduced Voltage while starting.

I am assuming when Jay Mills says the "T-stat ground wire", he means a Coolant Temp Sensor wire. Jay, if you are still monitoring this, it might help others if you could confirm that. The Thermostat is a mechanical device that opens to let water through - no wires. There is also a Coolant Temp Switch that controls the cooling fan, an Air Intake Temp Sensor, and another Temp sensor in the A/C. I would assume that the Temp Sensor is what you mean, but in my diagram it looks like it doesn't actually have a ground (and if it were a ground, why would it touching something else affect it?) - this runs between 2 different ECU terminals. You would expect to see erratic temp readings on the Dash if that was it.

Last edited by mattfiller; 08-02-2011 at 11:00 PM. Reason: add clarification
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Old 02-06-2012, 05:58 PM   #13
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Default Re: 93 civic fuel pump problem..

Quote:
Originally Posted by mattfiller View Post
Thanks, fcm.

Re-Soldering the Main Relay fixed a similar problem on my son's 1992 Honda Civic DX. The common thread to the times it would not start was that the interior was hot (car in sun, in Summer). This began late last Summer, we replaced the fuel pump, and it seemed fixed. Then this summer it sometimes wouldn't start in the afternoons, worked fine by night and in the morning. Sometimes, opening the door for a while got it working again. Of course, depending on the way the solder joint fails, temperature might have nothing to do with this on some other vehicles.

For a good picture showing how to find the bad solder joints, see Circuit Star-29's first post in thread ?? 97 Civic - ODD NO START SOMETIMES - no spark or fuel?? . This thread has other posts with instructions on re-soldering the relay, and some similar problems that also could be causes.

You could also just replace the relay unit, if $100 is cheaper than your time to re-solder it, or you suspect the contacts are bad. Haynes has a procedure for checking the relay, but it passed those tests every time. The location of the relay probably contributes to it staying hot; removing it to test let it cool and seem OK.

The pins for the 92 are marked on the relay, and my wiring diagram identifies them as follows:
1 - Always +12V (from ELD)
2 - Ground
3 - Fuel Injector Output
5 - +12V Run and Start (from ELD)
6 - +12V During Start only (from Ignition Sw via interlocks)
7 - Fuel Pump Output
8 - ECU Fuel Pump Signal FLR1 & FLR2
(IGP1 and IGP2 are grounds connected to the Main Relay Ground in the same harness, according to my diagram, for a 1993 Civic in the Haynes manual).

The Main Relay switches power for the Fuel Injector System and Fuel Pump from Battery, via the Electronic Load Detector (ELD). The injector system (and a few other devices) get +12V from this relay whenever the Ignition Switch is on (including Start). This also powers the second relay, through a resistor and diode, when the ECU signals the fuel pump by grounding the other end of the relay coil. The start power input apparently assures the second relay stays on despite reduced Voltage while starting.

I am assuming when Jay Mills says the "T-stat ground wire", he means a Coolant Temp Sensor wire. Jay, if you are still monitoring this, it might help others if you could confirm that. The Thermostat is a mechanical device that opens to let water through - no wires. There is also a Coolant Temp Switch that controls the cooling fan, an Air Intake Temp Sensor, and another Temp sensor in the A/C. I would assume that the Temp Sensor is what you mean, but in my diagram it looks like it doesn't actually have a ground (and if it were a ground, why would it touching something else affect it?) - this runs between 2 different ECU terminals. You would expect to see erratic temp readings on the Dash if that was it.
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Old 02-07-2012, 04:40 AM   #14
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Default Re: 93 civic fuel pump problem..

When they say T-stat housing ground wire they are referring to the bundle of wires that are physically bolted to the thermostat housing bolt. Look.
These wires contain the ground point for the main relay which is wired thru the ECU to this ground point. Clean these wires and the ground point. This has been a common problem.
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Old 03-16-2012, 11:05 AM   #15
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Default Re: 93 civic fuel pump problem..

i had the exact same problem but it turned out to be my alarm system after i took it out car worked fine ever since
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