Got a freshly built LS/V that only cranks but wont start. We have fuel, spark, compression, and timing has been checked multiple times. It will only crank but no sputter or anything EXCEPT about every 4 or 5 tries, it will backfire when the key is turned to the "RUN" postion, before even cranking the motor. Our minds are boggled. We have checked everything, tps voltage, resistor box resistance, spark, compression tested 180 across, timing is right on, fuel is getting to the cylinders, ect. We are using crome to get a base tune for start up and a street tune for break in. Getting professionally tuned this weekend. All provisions have been adjusted accordingly. Tried adding fuel and taking it away. Nothing except the random backfire. Did however check out the map sensor, and turns out it wasnt a 3 bar like we were led to believe. So it was switched out with a 3 bar from a buddies running car. Still wouldnt start though the backfiring issue became more frequent. By that time we had ran down a yellow top optima so we quit for the night.

I have seen the ls bottom end run personally. Its got eagle rods, CP 9:1 81.5mm pistons, and new water pump, oil pump, t-belt, ect. It was a buddies and had a ls head on it at the time. Only ran and idled for a matter of minutes then parted out due to a bad turbo and he gave up on it. He was using Precision 1000cc injectors which we also got from him and are using with this current setup.

Head was put together and tested at a local machine shop. Its got Blox dual valve springs and blox cam gears. Stock everything else. Bolted down with arp studs. Distributer was pulled from a running car. Replacing cap, rotor, and wires tonight for peace of mind.

Running a big Blox TB and TPS. TPS was tested at the unit itself and ecu and adjusted accordingly. Edlebrock IM and golden eagle fuel rail is also being used along with golden eagle ls/vtec kit.

Im sure theres stuff im missing but just wanna get this out there to see if anyone has any thoughts or ideas. Thanks for any help!!

 

was map in crome made/adjusted for the 3 bar map sensor?

 

Check your firing order...

 

Yes.

Triple checked.

 

I had this issue with a fresh rebuild and I forgot to check the valve lash.

 

Valves were already adjusted, I have good compression in all four cylinders.

 

swap it out for an oem ecu and injectors and see if it starts?

 

Thought about doing it, may have to come to that.

 

If you have fuel,spark, and compression in the cylinder and are not making a bang you would be the first.

How are you verifying that you have fuel. Pressure in the rail means nothing.

 

Exactly!! We pulled the plugs and you can see fuel on the piston tops. Plugs smell like fuel.

 

Its entirely possible its dumping too much fuel and fouling the plugs etc... I had this issue when I put big injectors in my Mustang. I had raw fuel dripping out the tail pipes while cranking the car. I pulled 30% fuel from the tune and got it to start and tuned it from there.

 

Thought of that, on our second set of new plugs, and tried pulling fuel out, no change.

 

I bring up firing order because you can have the order correct but the number one plug off. Have you tried "rocking" the distributor during cranking to see if the "back firing" changes?

I missed the part about it "popping" when you turn it to the #2 position. I would presume a bad ECU or faulty wiring/install. Regardless, what you describe sounds to be more timing related be it mechanical or ignition. What is your fuel pressure at the rail and what is your offset at? Also, have you tried starting it by opening the throttle at different angles (to try and overcome the fuel)? Or has it been all closed throttle?

Just trying to get the diagnostic ideas flowing.

 

Alright youre on our level...we went throught the firing order twice, its correct. We did think it was off by one but turns out it was right the first time.

ECU is good, no solid cell. Fuel pressure is 50psi when the pump primes. And yes we tried, half throttle, full throttle, ect but nothing changes. FYI the fuel system is completely aftermarket. Full stainless lines, an fittings, aeromotive fpr, big nasty pump.

 

Come on Honda-Tech!!!

 

Im reaching here but are you sure of the impedence of your injectors. Low impedence injectors with no box probaly wouldnt allow the motor to run.

 

Right, thought of that but im 99% postitive all Precision 1000cc injectors are low impedence, therefore a resistor box is needed which we are using and tested fine (6.8ohms at all four pins).

 

Sorry, I just realized you already stated that you had good compression

 

No problem, thanks for trying to help!!

 

Try a different chipped ecu.. Possible the chip didn't take the tune or the tune is actually not burnt to the chip.

Are the injector offsets correct? and Map setting is correct? Double check..

Pull the rail, and try to crank the car over, holding the injectors(will require more then yourself) watch the injectors fire, make sure they all fire. If they do, pull the plugs and check each plug is actually firing..Something is not allowing you to start. I've had a few cars have too tight a valvelash and it wouldn't even start or if it did, it would have a very bad miss to it..

Main relay clicking?.. Try jumping the pins and seeing if you get thrown any codes.

If i was there, i would be able diag it better.. You have everything to start the car, there's something underlining that you think you have, that you dont, thats not allowing you to start.

 

Make sure your injector wires,map wires and tps wires aren't crossed. Backfires are usually indicitive of timing order wrong, firing order wrong, or injectors aren't in the right order..

 

Simple question. What color's the spark?

 

Crome is saying its successfully comunicatiing and transfering with the ecu.

Triple checked.

Those are some things to definitely try for sure.

Main relay is good. We did jump the pins at the diagnostic plug and the CEL just stays on. Now our first thought was bad ecu, but to my knowledge a bad ecu would through the CEL on without jumping the plug correct? Like when turning the key on to run, CEL comes on while pump primes and then stays on...

Thanks for trying to help, but youre right, something just doesnt add up.

 

i would check all injectors like allmotor stated. Pull the rail and make sure there firing..I had a similar issue on my first build. Make sure u are getting power at each injector with IGN on. Use a test light. If you are then unplug each injector get a aligator clip ground wire. Ground the ground side of each injector and apply 12v power to power side and listen for a click.

In my case two were clicking the middle two were not, swapped those two with two oem injectors i had lying around ( all were oem for start up ovi in youre case you couldnt use oem) Once i changed them out it fired right up. Just an idea...Good luck.

 

Its very possible the resistor box is wired up wrong.