Crank No-Start/Idle 91 ZR-1

[BaggyToaster]

Hello everyone, I have been a long time reader of these forums and the information has been quite helpful. I have a 91 ZR-1 that has been plaguing my existence. I first diagnosed a crank no start as a bad ECM due to lack of injector pulse and continuity to ground through ECM when cranking. Had the ECM rebuilt and the thing started right up and ran like a top for 3 days. On the 4th day I shut the vehicle off and when I went to restart it, it died instantly. I have initial injector pulse for cold start key on for all injectors. It cranks, fires off of initial pulse fuel, then dies within 2 seconds. I have good spark at all plugs, good cam and crank sensors with good continuity to ignition control module. The only thing i am losing is injector pulse once cranking. I have no ECM or CCM codes. Could the ECM have gone belly up again? I have hit a wall and would appreciate any feed back or additional diagnostic routes that I have not explored. I have a FSM for the vehicle as well.

[Marc Haibeck]

Try these two suggestions.

Is there a VATS lockout? With the door open and the ignition key off the Security light should be blinking. Close the door and try to start the engine. Is the Security light off when you have the ignition key on?

Observe the fuel pressure when the engine is cranking and not firing. The fuel pressure must be over 30 psi for the engine to fire. What is the fuel pressure while cranking?

Marc

[BaggyToaster]

Security light flashes normally. Key in and ignition on, security light goes out. Starter cranks normally but engine will not continue to run. Fuel pressure is good and does not fluctuate while cranking.

[Marc Haibeck]

The future of your ECM is not looking good. Maybe it has a poor internal connection. Have someone bang on the ECM with their hand while you are cranking the engine. Beyond that, try to find another ZR-1 that you can swap ECM's with to confirm the defective ECM.

Marc

[BaggyToaster]

I will give that a shot. Don't know of any other C4 LT5s in the area but I will be on the lookout. We had the ECM rebuilt so it has a warranty. Thank you very much for the help.

[Corvette95]

May I ask who rebuilt the ECM?

[BaggyToaster]

ZR1ecm.com. Sorry I was away for a few days.

[Corvette95]

ZR1ecm.com. Sorry I was away for a few days.
Thanks. Never heard of them but if they CAN truely fix a ZR-1 ECM that would be wonderful. Your experience with make makes them look kinda shady.

[BaggyToaster]

I wouldn't label them shady quite yet. We have been in communication with them and so far they have tried to help resolve the issue. The rebuild did come with a warranty. All we can do is give them a chance to fix the issue if it is in-fact a defective ECM. I have a couple more advanced diag steps to try. I am going to try to mimic a crank signal from the Ignition module to the ECM to see if I get injector pulse, if that does not show results the ECM is definitively the issue. I will do my best to update.

[BaggyToaster]

I have finished performing the more advanced testing, continuity and resistance testing of all fuel injection related wiring. All results point towards a faulty ECM. I did notice that the engine bay was dirty when it left after the last ECM rebuild, and then when it came back for more diag into the selective ride system, the engine bay was very clean. water intrusion could be the culprit to the rapid ECM failure. Will post what the rebuilder finds.

[Ozruss90]

Your symptoms sound the same as mine, that I have overcome in the last couple of days. I thought my Cam Sensor was ok BUT upon advice from Marc, I disconnected the wiring harness from the Cam Sensor to the ECM. Engine fired up and ran straight away. Put another Cam Sensor in ( borrowed secondhand) and car is back to normal.
Hope this works for you 🤔

Cheers,
Russell 🇦🇺

[BaggyToaster]

Your symptoms sound the same as mine, that I have overcome in the last couple of days. I thought my Cam Sensor was ok BUT upon advice from Marc, I disconnected the wiring harness from the Cam Sensor to the ECM. Engine fired up and ran straight away. Put another Cam Sensor in ( borrowed secondhand) and car is back to normal.
Hope this works for you 🤔

Cheers,
Russell 🇦🇺

I read your thread right after I posted my latest update. I was skeptical that it would work mainly due to not having any injector pulse. I still ran out and tried it immediately. Unfortunately no workie. Thank you for looking out!!!

[RSLyrick]

Hi Baggy,

even if your tests results highly suggest that you have a faulty ECM, would you have a ZR-1 friend around to perform a swap test to finally confirm it ?

If not, I guess the cheapest option at the moment is to use your warrantly. The technician who performed repair should be able to confirm the failure by placing your ECM in its own test car and then investigate if the failure is related to the rework or something new.

I do not see ECM for sale on Ebay or corvette forum so far.

[BaggyToaster]

Howdy everyone, I would like to post the fix and round out this thread. We received the ECM back from rebuilder on 12/4 and installed it on 12/5. Vehicle started and ran like a top! Rebuilder said that some solder bridges on the original boards were cracked, some broken, and were missed on the original inspection.

Thank you all for your help, knowledge and support. Learning a new system and diagnosing it has added another feather to my cap. I wish you all a Merry Christmas, Happy Holidays, and a great 2025!!

:saluting:

[Ozruss90]

Howdy everyone, I would like to post the fix and round out this thread. We received the ECM back from rebuilder on 12/4 and installed it on 12/5. Vehicle started and ran like a top! Rebuilder said that some solder bridges on the original boards were cracked, some broken, and were missed on the original inspection.

Thank you all for your help, knowledge and support. Learning a new system and diagnosing it has added another feather to my cap. I wish you all a Merry Christmas, Happy Holidays, and a great 2025!!

:saluting:
Glad to hear that you?re back up and running again Baggy.

Cheers, and Merry Christmas from down under.
Russell 🇦🇺

[XfireZ51]

Good to know there may be a vendor for restoring ECMs.

[Dynomite]

Sounds like zr1ecm.com (Macroblock) can fix ZR1 ECMs 👍

ECMs with some solder bridges on the original boards cracked, and some broken.