failure to start after warmed up

[orthodoct]

Gentlemen:
Brand new problem. Car running fine after rebuild. Had my hair cut yesterday and got 92 ZR1 up to operating temp. Got back in car to go home about 30 minutes later. Starts, runs 3 or 4 seconds and dies. Throttle appears unresponsive at that time. Started about ten times then had to be towed home, seventy five bucks wasted! Once cooled down to below about 150 degrees oil temp, started just fine. Suspected fuel problem, but even with problem, Schrader valve on fuel rail is pressurized. Ran diagnostics this AM and no codes are set. Neither FP1 or FP2 fuses open. Fuel pump/sender unit is new and got it from Jerry about a year or so ago. Fuel filter changed when new pump assembly installed. Started this AM and ran up to operating temp of 192. Restarted immediately, but when attempted to restart ten minutes later, once again starts and runs 3-4 seconds and dies. No evidence of fuel starvation at WOT when running. I read about potential problem with loss of primary fuel pump and fact that both primary and secondary pumps run on startup (until 176 degrees I think that I read??) and then secondary shuts down except when secondary injectors come on line. If primary pump dead, would expect fuel starvation at WOT and it is a new unit. 92 ZR1 owned since new, Haibeck chip, new injectors from Jerry, rebuilt everything under plenum, new clutch from Bill Boudreaux, Stainless Works headers with Corsa exhaust. Has run flawlessly for over a year until this happened. What to do???
Thanks!
Ty (orthodoct)

[Jagdpanzer]

Sounds like the same problem I had right after acquiring my 94 ZR-1 ten years ago. Turned out to be the primary fuel pump had seized up. When first starting cold the ECM runs both fuel pumps until 176 degree F coolant temperature is reached. Then it cuts back to just the primary fuel pump. If the primary fuel pump is not working the engine will immediately shut down due to lack of fuel pressure. However, when you try starting the engine again with engine still at or above 176 degrees F ECM runs both fuel pumps until the engine reaches 400 rpm whereupon the secondary pump is cut off again. This could explain why your engine runs for a few seconds and then dies. You can verify by letting the engine cool down longer then try starting it again to see if the engine runs longer before dying. Be sure to watch the digital coolant temp gauge and note the temp reached.

[GOLDCYLON]

Another possibility is the clutch switch needs to be bypassed. If you type in search a lot of documentation of that process as well. If you had a fuel jumper you could plug it in to determine primary fuel pump beginning of failure.

[orthodoct]

Thanks Jagzpanzer. The only problem with that theory is that the engine should die immediately upon reaching 176 degrees F+/- and it doesn't. It runs just fine at its stable temp of 192 degrees until I turn it off. If I restart it immediately, no problem. If I wait ten minutes, it starts and immediately dies after 3 or 4 seconds with the throttle having no effect. If the pump were seized, it should have drawn enough current to have popped the fuse and it didn't. I have a fuel pressure gauge that I can attach to the Schrader valve and measure pressures, but haven't gotten that far yet. I checked for ECM and CCM fault codes via ALDL connector and there are NONE; either C12 or --- everywhere. Now, I have had a ham radio license since I was 15 and what do you folks think of this theory? Jerry and Mark, need some input here if you have a chance! When the engine is turned off after heating up to full temp, the plenum gets hotter. Could the TPS sensor or the manifold absolute pressure switch be causing symptoms like this??? I thought about the CCM/ECM (the one under the hood!) heating up so I purposely left the hood up with my last test to prevent it and was still able to reproduce the problem. I THOUGHT that I smelled a fried electrical smell coming from the vicinity of the TPS sensor when this first happened, but could have been mistaken. My understanding is that the TPS sensor is just a potentiometer that varies output from about +0.5v at idle to +5.0v at WOT. I checked the fuel regulator, the diaphragm is intact, but sucking on one of the hoses going into the plenum did have a bit more gas odor than I would have thought. The hose to the MAP is intact and the short one going from the regulator to the plenum is new (from Jerry). Checked them both. Starting to really suspect that MAP sensor becoming unstable/defective when heat soaked. Friend Goldcyclon, what is this about a fuel bypass harness that I just saw? Did I miss a group buy or something? Did you get the metric pins for the shock gears that I sent you? Thanks, guys. We'll get this fixed and it will add useful info to our database for when it happens to somebody else. Thanks for the help, as ALWAYS! When that car died, it did so in front of a local repair shop. I had enough sense to have it towed home. Guarantee you that they had never even heard of an LT5 before and mine wasn't going to be their guinea pig. You know, we folks on this forum have become the world experts with regard to that car and you folks on this forum make me feel like a knuckle dragging idiot!!
Thank again!
Ty

[karlaw]

I will be watching close at this post. How do I check fuel regulator, and where is it located ?
My 2 No Start cars are driving me crazy.


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[orthodoct]

Hi Karlaw. Fuel regulator is at back of plenum, has a round black top with a vacuum connection. Fuel lines run into it. It has a sensing diaphragm in it. If the diaphragm is ruptured, it will allow raw gas into the plenum and can't regulate fuel pressure. Best way to check is to see if the hose connected to it has liquid gas in it. It should not. If engine is running and you remove hose and diaphragm is defective, will spray gas so be careful. Gurus, let me know if I am in error.

[QB93Z]

Car starts warm and dies after 3-4 seconds if the primary indication of a failed or failing primary fuel pump. I have had it happen 4 times in my ZR-1's. The pump is easy to change and then you will be able to look for other problems.

Note: I have seen a case where the secondary fuel pumps internal check valve failed intermittently and the primary fuel pump discharged was "short cycled" in the tank. Net result, car would run poorly and sometimes die immediately after a warm start. But it would run great at full throttle because the secondary pump check valve was not a factor with the secondary pump running.

A fuel pressure gauge on the fuel rail during the period when the car was running poorly identified the problem.

Jim

[orthodoct]

Thanks, Jim. I have a fuel pressure gauge. Will check it out. Sounds like failING is the operative term here since it runs fine at partial throttle even when warmed up and secondary pump shuts off if I follow your logic correctly.
Thanks!
Ty

[QB93Z]

BTW, I have seen many failed fuel pumps and have never seen one blow the Fuel Pump Fuse. It has probably happened but I have never seen it.

Jim

[orthodoct]

Thank you, Jim. What would you expect normal fuel rail pressure to be??


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[QB93Z]

Fuel rail pressure is a variable. The system is designed for a constant pressure differential across the injector. The pressure in the Intake Plenum varies with throttle position, from high vacuum at idle to atmospheric pressure at full throttle. Therefore the Fuel Pressure Regulator is connected to plenum vacuum and adjusts fuel rail pressure to follow the changes.

As a rough check fuel pressure varies from 40 to 50 psi under normal conditions. The highest pressure you would see is with fuel pumps running, engine off, Ign ON/Engine OFF.

The Field Service Manual gives exact parameters for testing and evaluating the FPR.

Jim

[A26B]

Ty,
My first replacement pump choice would be Delphi FE0039 $49.79 Rock Auto

My Second Choice would be Airtex E3240 $38.79 Rock Auto

I would also recommend replacing all of the plastic hose clamps with ss worm clamps. Be sure to rotate the gear housing to the inside to make it easier to install.

Jagdpanzer & QB93Z are spot on. QB93Z probably has more real-world experience than anyone, considering the incredible trips he & Lindy have taken in ZR-1's and the years of volunteer support of time & facilities he has given to the WAZOO group. I'm proud to know them both personally as great friends.

[orthodoct]

Thank you, Captain! You were exactly right. I just talked to Jerry an he told me that you were great friends. He and I have corresponded quite a bit over the years. Going to order a new pump from him tonight. Put in a friend request, if you don't mind. Will update once the new pump is installed to bring some closure to this thread.
Best regards.
Ty

[karlaw]

Thanks orthodoct, I am going out to inspect both my cars. I am also anxious to get a fuel pump jumper to try to help diagnose my no starts.


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[orthodoct]

Good luck, my friend.
Ty

[orthodoct]

Good luck, my friend.

Ty



Sorry for long delay. Had a KNEE REPLACEMENT five weeks ago. Did a couple of thousand of them before I specialized my practice to shoulder and knee arthroscopy. Hurt like HELL and takes forever to get over. Finally well enough for some standing up tinkering. Checked fuel pressure below 176 and read 42psi. Ran to operating temp which is 192 with Mark's chip. Shut down and restarted fine. Waited 15 minutes attempted restart. Wouldn't start. Fuel pressure varied from zero to ten psi. Hobbled around a couple of weeks and changed pump assembly yesterday. Scared the hell out of me. Ran fine on warmup, but when I punched the secondaries in neutral, I killed every mosquito in the neighborhood. Scared that I had a broken valve or ring or something, but smoke symmetrical from both pipes and no oil odor. Dawned on me that I had disconnected negative battery terminal prior to pump change (I'm a private pilot as a hobby and burning to death ain't high on my bucket list) and I think that computer settings went to rich default settings and car hadn't been started since before my surgery so old gas in secondary injectors, "blowing out carbon", etc. ANYWAY, went for a short drive to reset everything (with GOLDCYCLON's trusty bypass jumper in my console just in case) and everything runs JUST FINE, problem solved. I promised to try to close this thread once less crippled and I'm glad that it had a happy ending. As usual, thanks to the brilliant guys with the Registry with whom I am proud to be associated. Special thanks to my friends the Captain, GOLDCYCLON, and of course Jerry without whom many of our cars would no longer be on the road.
Ty


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[GOLDCYLON]

Glad you got her up and running again. Take it easy on the knee. GC

[orthodoct]

Glad you got her up and running again. Take it easy on the knee. GC



Thank you, my friend!
Ty


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[5ABI VT]

Happy to hear it was solved.

[orthodoct]

Happy to hear it was solved.



Thank you, me too!!


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