Conversions & Hybrids - problems with first start on rebuild
07-10-2012, 06:23 PM
i have a conversion vehicle. i transplanted an ls1 into it. i'm running a procharger. the motor was completely rebuilt a couple years ago with all forged internals. so a couple days ago i finished putting everything together, turned the motor over with the fuel pump disconnected until i got 20-30psi on my oil press gauge. i then hooked up the fuel pump and attempted to start. about 20 start attempts later the engine will not run. the most i get is about 5 seconds at idle. when it idles it seems to run smooth, but doesnt last long. i hooked up my scan tool, and it said map circuit high output. i got a new map sensor, no change in results. however now the scan tool says mpa circiut low output. i put my vom on the plug and got 5 volts from pin a to c. i beleive this is the expected value. i dont know what else to check with this circuit? i am at a stand still now. i checked with my tuner who gave the ecm an initial flash. he said he deleted the vats. i'm stumped, please help.
07-10-2012, 06:53 PM
Feel your pain, I wish I could help.
07-10-2012, 07:15 PM
Check the basics, make sure you have fuel good pressure, check for spark, check to make sure the injectors are firing with a noid light or similar.
07-11-2012, 02:06 AM
Runs good for 5 seconds and dies...
Delete VATS in the pcm.
07-11-2012, 02:08 AM
Gonna have to double check the VATS. that sounds exactly what is going on.
07-12-2012, 11:26 AM
That's what my initial thought was too.(vats) vendor swears up and down he already deleted it. I'm still getting the map circuit trouble code too. I get 5 volts across the plug pins though which I believe is correct. I don't know what else would keep giving me that code. I will check fuel pressure today to rule that out. Maybe change the map sensor again. ???
07-12-2012, 08:45 PM
so i double checked the fuel pressure today. when the pump primes it builds up to about 58psi, then it drops to about 52 when the pump stops. when i turn the key to start it pops back up to 58 and stays there until the motor dies..........again. i also replaced the map, again. same results, car starts every few times, runs for a few seconds then dies. so now i'm wondering, what would cause the map to be stuck at it's high or low limit??? either high or low pressure right? but what could cause this? and why would it switch from the high to low limit?
07-16-2012, 10:18 AM
pump stops due to no oil pressure signal.then pressure drops due to leak in system--could be an injector or the fuel pump,or the pressure regulator. if it stays at 50,no problem. then when you go to start,the pump starts again.
07-16-2012, 11:38 AM
KOEO, what does the MAP sensor read?? Should be about 100KPA, depending on your altitude....
07-17-2012, 08:18 AM
Just for the record... When I bought my donor car, I watched the guy delete vats. As far as I knew, and he knew, it was gone.
When I went to run my car for the first time, sure enough it was back. I built a bypass box for it real quick with radio shack parts just to test out the theory and sure enough it ran perfect.
So I bought a nice aftermarket bypass, and used it as a security device. Ide unhook it and take it with me since it was tiny. THEN...after a while, the car started to run with out it...?
VATs can do some funky things is my point. Search under my name, or for vats bypass if you want to see how to build one yourself really cheap and easy. If you can solder, its a couple bucks and 30 minutes work. Hook up is easy and it'll confirm its vats. Thats IF youre using the stock PCM and have exhausted all other obvious possibilities.