Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

May I ask who rebuilt the ECM?

Re: Crank No-Start/Idle 91 ZR-1
 

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

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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 🇦🇺

Re: Crank No-Start/Idle 91 ZR-1
 

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!!!

Re: Crank No-Start/Idle 91 ZR-1
 

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.

Re: Crank No-Start/Idle 91 ZR-1
 

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:

Re: Crank No-Start/Idle 91 ZR-1
 

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

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

Re: Crank No-Start/Idle 91 ZR-1
 

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

Re: Crank No-Start/Idle 91 ZR-1
 

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

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

Re: Crank No-Start/Idle 91 ZR-1
 

What did they charge to repair your ECM? What was the turnaround time?

Re: Crank No-Start/Idle 91 ZR-1
 

I can confirm, I have been able to repair almost every C4 Corvette ZR1 ECM I've worked on. The few that are not repairable I strip for parts.

Based on the numbers, there are 10-15 ECM failures per year. Of the ones I've worked on, IC's U13, U15 and U4 are the most troublesome.

Baggy Toaster's ECM had a defective U13. In this instance I was forced to substitute his defective U13 with a discrete outboard microcontroller to perform the functions of this IC.

The difficulty with these ZR1 ECM repairs comes from lack of parts. There are none. More often than not, I am forced to invent a workaround for an ECM's specific failure. This is very time consuming.

Fortunately, I have a hardware and software background in electronics, so I was able to create a bench-top ZR1 ECM emulator, which provides much faster diagnostics than testing on-car.

My work comes with a 2-year warranty.