Hard starting 93 LT1
02-15-2017, 07:51 PM
#1
Hard starting 93 LT1 Weird problem. It seems like the only times it will start right up, is when the engine is at ambient temp, or if I turn the car off and start it up again as soon as I turn it off. Letting it sit say, 20 minutes or more, it's hard starting. I ran a fuel Pressure test.
Key on, engine off: 42 PSI
Engine running, 38 PSI
Snap throttle test looked good as well, no PSI drop when stepping on it.
Bleed down rate at 10 mintues, no fuel pressure loss. It stayed at 42 PSI.
When I unplug the FPR vacuum line, it simulates WOT. Went up 46 PSI when the line was disconnected.
No codes either.
The car is on LTCC(coil pack conversion) so that eliminates the coil and ICM. Problem existed before this, so LTCC is not the problem.
No fuel present in the fuel pressure regulator
I do datalog. Temp reading for coolant on datalog and on my car always agree. Coolant sensor, wiring and connection is good.
Cycling the key multiple times to prime the fuel pump changes nothing.
93 LT1 Corvette
No codes
On the hard starts, it will idle rough for like a minute. But runs fine.
Key on, engine off: 42 PSI
Engine running, 38 PSI
Snap throttle test looked good as well, no PSI drop when stepping on it.
Bleed down rate at 10 mintues, no fuel pressure loss. It stayed at 42 PSI.
When I unplug the FPR vacuum line, it simulates WOT. Went up 46 PSI when the line was disconnected.
No codes either.
The car is on LTCC(coil pack conversion) so that eliminates the coil and ICM. Problem existed before this, so LTCC is not the problem.
No fuel present in the fuel pressure regulator
I do datalog. Temp reading for coolant on datalog and on my car always agree. Coolant sensor, wiring and connection is good.
Cycling the key multiple times to prime the fuel pump changes nothing.
93 LT1 Corvette
No codes
On the hard starts, it will idle rough for like a minute. But runs fine.
03-16-2017, 09:10 PM
#3
Late to the party, but issues only when hot are 99% of the time electrical related. Normally I would jump straight to ICM, but since you replaced that with the LTCC setup(that may have its own issues, I have no personal experience with it and documentation is lacking on them) you could have possibly replaced a faulty ICM with a faulty LTCC setup. Stranger things have happened!
Next I would point to the coolant sensor, but you already datalogged it and verified it reads correct. The 93 is a simple speed density setup, so that leaves the MAP sensor as the next logical culprit.
Test the MAP with a DMM, voltage should drop from 4.7v on the signal wire down to ~1v as it gets vacuum. If you don't have a vacuum pump, you can suck on the nipple (giggity) and notice a smooth decrease in voltage. Unless you have Superman lungs you won't get anywhere near 1v, but thats not important.
Next I would point to the coolant sensor, but you already datalogged it and verified it reads correct. The 93 is a simple speed density setup, so that leaves the MAP sensor as the next logical culprit.
Test the MAP with a DMM, voltage should drop from 4.7v on the signal wire down to ~1v as it gets vacuum. If you don't have a vacuum pump, you can suck on the nipple (giggity) and notice a smooth decrease in voltage. Unless you have Superman lungs you won't get anywhere near 1v, but thats not important.
02-26-2018, 12:40 AM
#4
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I have same issue with my 95 Z28. I've had every test ran. Changed the O2 sensors. Cleaned the MAP sensor. Had fuel pump checked.. All was good. Been like this for four years now. When car is cold, I just turn the key far enough to hear fuel pump run till it stops but engine does not turn over. Do that 3 times( letting fuel pump run till it stops) then car should start right up with no over cranking issues. Like I said I've been doing this for four years. Many mechanics and computers could not find any problems. When car is warm, I don't have to run the pump like I do when cold. Hope this helps ya out.
02-28-2018, 09:25 PM
#5
Sorry for the year late reply. No I have not. Other than that, car runs fine.
I bought a new ICM, still did the same. LTCC was bought brand new. Saw this thread was bumped, that is why I am responding.
Late to the party, but issues only when hot are 99% of the time electrical related. Normally I would jump straight to ICM, but since you replaced that with the LTCC setup(that may have its own issues, I have no personal experience with it and documentation is lacking on them) you could have possibly replaced a faulty ICM with a faulty LTCC setup. Stranger things have happened!
Next I would point to the coolant sensor, but you already datalogged it and verified it reads correct. The 93 is a simple speed density setup, so that leaves the MAP sensor as the next logical culprit.
Test the MAP with a DMM, voltage should drop from 4.7v on the signal wire down to ~1v as it gets vacuum. If you don't have a vacuum pump, you can suck on the nipple (giggity) and notice a smooth decrease in voltage. Unless you have Superman lungs you won't get anywhere near 1v, but thats not important.
Next I would point to the coolant sensor, but you already datalogged it and verified it reads correct. The 93 is a simple speed density setup, so that leaves the MAP sensor as the next logical culprit.
Test the MAP with a DMM, voltage should drop from 4.7v on the signal wire down to ~1v as it gets vacuum. If you don't have a vacuum pump, you can suck on the nipple (giggity) and notice a smooth decrease in voltage. Unless you have Superman lungs you won't get anywhere near 1v, but thats not important.
03-01-2018, 03:05 PM
#6
11 Second Club
I had the same problem with my first Camaro (94’Z28) and I was thinking it was the mass air sensor but Katrina flooded the car before I could diagnose it.. But since yours is a 93’ without mass air sensor idk what would cause that.. One thing I could say is that the car lost power real bad one day.. I nailed it and “nobody was home” felt llike it was starving.. I got to my destination and checked the air filter and sure enough it sucked in a grocery bag somehow.. Thats when the car started having the same symptoms as yours..
Last edited by NewOrleansLT1; 03-01-2018 at 03:12 PM.