1994 LT1 6-Speed

Car starts up fine when cold, and drives perfect. No issues at all while running. After the car has gotten up to temp and you shut it off, sometimes it will just crank and crank and not start. Sometimes it will start and the car will surge for a second and then die. Other times it will start up just fine like there is no underlying problem at all.


I think I have narrowed it down and here is where it gets interesting. After you shut the car down after a drive, and you go to restart it, the fuel pump will not prime. You can audibly hear it not turning on. When it does this, the car will either just keep cranking, or it will start up and surge and then die. If I wait 10 seconds, and try again, you can hear the fuel pump prime, and the car will start right up and run as it should.


My question is, what is causing the fuel pump not to prime after it gets warm. Is this a VATS issue? I installed a VATS bypass module from Ecklers back in 2011, and had PCM for less delete the VATS system in early 2014 so I feel like this isn't the issue. I tried a spare key just for $h!ts and no difference.


I was having similar issues in February and a fuel pressure check showed 10-15 PSI when I went to restart the car when hot. So I chalked it up to a bad fuel pump. Replaced it with an AC Delco. Seemed fine, but I guess the problem wasn't resolved and now that summer is here it is more prevalent. This doesn't happen every time. Generally, if I run the car very hard, and then shut it down, I cannot restart it for at least a couple minutes. What is causing the fuel pump to intermittently not to prime after the car gets hot?

 

Did any volt testing during the not priming times?

 

The puter will run the pump for two seconds before starting maybe just a bad connection or relay.

 

Im guessing a tiny leak on one of the hoses - it can even the pump hoses. Or your new pump is poop already. Check your fuel press again.

Sorry to read the bad news so soon.

 

Thanks so far guys...

Did some more testing.

I let the car cool off for about 3 hours. Turned the key and the pump primed, it started right up and let it run for about 2-3 minutes with the fuel pressure gauge hooked up. Stayed around 40 PSI the entire time. Turned it off, and then tried to restart within 30 seconds, the pump did not prime this time, and the engine cranked over a few seconds before starting. Once it started it ran very rough and the fuel pressure dropped to around 15-20 PSI before it eventually died. The fuel pressure remained at 15-20 even with the engine off, so I am going to rule out injectors leaking down for now.

However, now the car won't prime at all, even when its cooled off. I am thinking maybe the fuel pump relay. Hooked a volt meter up to the fuel pump fuse locations and when you turn the key to "on" it gets .5 volts at the "FP1" fuse and no voltage at all at the "FP2" fuse. It seems like something between the ignition and the fuse is not operating correctly, and I am leaning toward the fuel pump relay.

Is there a way to bypass the fuel pump relay and fuse to verify if the pump will work at all?

 

I am sure there is but from what you have done I would spring the ten bucks and buy a relay.

 

Anybody have the correct part# for the relay?

 

I found 14100455 but double check

 

That appears to be the correct one. Ordered from Rock Auto, should be here soon. Might try and swap the one in there now with another one just to see. As of last night, the fuel pump was not priming at all (hot or cold) and not starting either.

Hopefully its a quick fix, if not, I'll spring for the Racetronix kit.

 

While your waiting look for loose and bad connection clean all.

 

Update:

14100455 is not the correct part# for the fuel pump relay on a 94'. 12065125 is the correct OMRON part #.



I have not been able to replicate the hard start when hot issue.

I accessed the fuel pump relay under the passenger side hush panel and swapped it with the fog light relay (same relay) with no change. I did notice it was very hot compared to all the others. Fuel pressure is at a constant 38 lbs. while idling with the fuel pressure regular still hooked up to vacuum. Does not bleed down when turned off either.

Still not sure where to go from here. Starting to lean toward a faulty intermittent fuel pump even though it is an AC Delco that was installed in February. Will try to drive it more tonight and see if I can replicate the issue I have been having. Weird how it can go from not priming or starting at all to acting perfectly normal with no change in anything really. I am convinced this car is possessed in one way or another.

Any ideas? Anything else I can check or trouble shoot outside of removing the sending unit?

 

My memory is real foggy on this but I think I remember reading a thread about how the fuel pump is grounded.If the ground contact isn't good of course youre not getting power to the pump then.

I think you need to find a way to check the voltage as near to the pump itself, when its not priming, or check out all the electrical connections from the pump to the front of the car. Including the ground.

 

A faulty ICM (ignition control module) can cause a start delay when the engine is 'hot'. Often, a faulty ICM will cause the car to 'die' when driving. When replacing the ICM, make sure the special grease is liberally applied.

From post #21 from this thread:
https://www.corvetteforum.com/forums...-symptoms.html

Quote:
Originally Posted by Stealthvette View Post
I have done the same. I would have to assume that the IM is the culprit because changing it is the only thing that gets the car running again. Any ideas why this is what works?
...again, in EVERY CASE that my car wouldn't start, when i changed out the ignition module the car would start and run fine...i have no loose connections, no bad or dirty connections, and the only thing i changed out that was NEVER changed out and was in place and common to all installations of all my ignition modules was the capacitor assembly, which i changed out a few weeks ago....

 

Hope you figure it out, Patrick. My car has been troublesome lately as well. I've had hard starting issues for a few months now. New plugs, plug wires, injectors and AC delco FPR didn't help. I need to buy a fuel pressure gauge for my car. Anyone specific one you recommend? Have you checked your injectors for leaks? Very easy to do. Doubt VATS has anything to do with it. It wouldn't crack at all if it did

 

Thanks for the reply! The car actually had a new ICM with new Thermal Paste from Radioshack before I ditched the factory ICM and Coil in lieu of the LTCC Coil per cylinder kit.

This for sure isn't an ignition issue, but a fuel related issue. I physically watched the fuel pressure gauge drop to zero and the engine cut out.


Thanks Brandon, I bought an Actron gauge from Advanced or Autozone a few years back. Seems to work fine. Just don't tape it to the windshield and try to close the hood like some on here have suggested or you'll crack your windshield (ask me how I know).

I haven't lifted the fuel rail off the manifold and checked for any leaks with the fuel pump primed, but just by looking at the fuel pressure gauge I can see the injectors aren't leaking down once the system has been primed. It holds pressure for a very long time.


Thank you! Going to retrace the wiring and run some more voltage tests. So far everything has been checking out, which I hate. Wish the problem would just rear its ugly head. It never does with this car.


I ordered the racetronix kit with the 190l/ph pump. Looks like this kit also deletes the pulsator which is another problem prone area with high miles. Hoping for a fix.


Just want to reiterate what I wrote in post #11. I have not been able to get the car to act up again. I am no sure if it just decided to be nice for a while, or if switching the fuel pump relay with the fog light relay actually fixed the issue. I am sure there is still an underlying problem that will show up at the worst possible time. I am decent at diagnostics but anything electrical and I start to get a little lost. Easy to check grounds and voltage though, but I feel this isn't painting the entire picture.

 

Update:

What I've done:

-Replaced fuel pump relay
-Replaced "made in China" AC Delco fuel pump with the Walbro Racetronix kit.

I have not had any problems since. Car seems to be running and starting as it should.


Couple notes about the racetronix kit:

-Make sure the wire harness they supply with the kit is wired correctly. On my kit they had the wires at the pump connector backwards which made the pump run backwards. This resulted in a really loud pump and no pressure at the rail. It was essentially just pumping air into the tank. Once I found this and corrected this all was well.

-Their gasket, and stainless fuel sender bolts make the kit worth the price over any other pump replacement out there.

-The pump runs much quieter than stock, I can barely hear it prime. The only way I know its priming is I can audibly hear the pressure building at the fuel rail.


Just want to thank everyone for the help, one of the best forums I've been on.

I just bought a house, so I am trying not to tinker with the C4 for a while. Going to give it a nice detail after work tonight and put it under the car cover for the next few weeks until I get re-situated.

 

Glad the car is doing good

 

 

Good u got it fixed. Cool how u sorted things out. I think u should be giving advice on the forum now rather than asking.

FYI i installed a Racetronx pump once (in my Z28) but w/o theyre wire harness. It only lasted like a year for me. Seemed expensive for that short time. I found the pump is a Walbro and u can buy from cheaper sources if needed. I do have a habit of sometimes running out of fuel though - i dont think its good to dry out the pump.