94Z28rag

iTrader: (10)

This is a weird one that both my tuner and I cannot figure out. Quick synopsis of the issue:

After the car has been dyno tuned via HP Tuners, the car will not start after it has sat for more than 15 minutes with the cutoff switch "off." The cutoff switch kills ALL power to the car as this is a track car. When I try and start it the first time, it pops and sputters but will not fire. When I switch the ignition off and on again (essentially resetting the PCM) the car fires without any hesitation.

What am I missing? There shouldn't be any issue with killing the power to the car and starting it up right away. I'm not getting any codes. I'm not overly familiar with the LS PCM, so is there some nuance that I am not aware of?

Thanks in advance for any help...

Ed Wright

iTrader: (1)

Turning the key off & back on does not reset the PCM. More likely your fuel pressure is falling off while setting. I would put a gauge on it. A stock vehicle in good condition will maintain fuel pressure for half an hour or so. Also pops right back up to normal in the short time the pump runs when the key is first turned on. Also your fuel pressure may not be coming up fast enough. That would explain not starting until the key is turned off and back on. Might take that second fuel pump cycle to get the fuel pressure all the way back up. I have seen several Walbro pumps cause this. Leaking relief valve in the pump causes the pressure to drop too fast after being shut off.

Btw, modified engines often also like longer injector pulse widths when cranking.

Hope this helps.

94Z28rag

iTrader: (10)

Thanks Ed. My fuel pump is on a separate switch and not triggered by the PCM. I wired the car from scratch using a Painless harness and switch panel. I always turn the fuel pump on several seconds before cranking the engine, but can try to cycle it longer to see if that helps. I don't have a fuel pressure gauge but will throw one on to see what we get on the initial hit.

The part that is confusing me is that, without fail, the car starts after shutting the ignition/PCM off and turning it on again. It may just be coincidental.

94Z28rag

iTrader: (10)

One other thing to note: The car never did this before the LS PCM swap. Nothing in the car changed other than the 24x conversion.

Ed Wright

iTrader: (1)

I have Aeromotive stuff in my race car. It does not hold fuel pressure when turned off like a factory system. Mine starts better if I count to 3, after turning the pump on & cranking the starter. Since all LS & Vortec engines use 60psi, they do not use as long of injector pulses as an LT1. Surely your tuner knew to add plenty of cranking fuel. Might ask him.
Good luck.

94Z28rag

iTrader: (10)

Talked to my tuner. No issue with cranking fuel. I'm going to swap another PCM and see if that helps.