Hello everyone, I've been dealing with a strange problem on my 86 for a long time. The engine sometimes shuts off while driving and won't start for about 2 minutes.

It usually goes like this:
A cold engine starts without any problems. The engine behaves perfectly normally for about 5 minutes. When the engine is almost warmed up - approx. 85°C oil temperature - the engine sometimes shuts down out of nowhere. Can't start for about 2 minutes. At the roadside, the mechanic and I tested that in this dead state there is fuel pressure on the rail and the spark plug gives a spark. After I let the car rest for about 2 minutes, the engine starts on the first turn of the key and runs like there is no problem at all. Sometimes the problem happens once again within a few minutes, but usually the Corvette drives the rest of the day without a problem. Sometimes diagnostics will show error 41.

I have already replaced:
ECM
PROM
Distributor, wires, spark plugs
Fuel pump

I am running out of ideas and unfortunately the fault is rather difficult to diagnose. Within 2 minutes somewhere on the side of the road, there is not much chance to properly investigate and diagnose something, and the fault never happened to us in the service, even if we let the car run for an hour.

If anyone has already dealt with something similar, I would appreciate your advice. Actually any advice would be greatly appreciated.

 

When you own a C4 look for the obvious. If you have a OB1 then it is even harder to diagnose, a Corvette only shop is your best bet! If you have a OB2 then you might have a chance. It could be fuel related and if you have a opti maybe.

 

Have you thought about the ICM or coil even though you have spark, time between failure, testing and cooldown?? I would want to see the pulse width for the injectors as well. Could one injector be shorting out, noid light ??

Is fuel tank vented properly ?? new / old gas cap without the correct or failing vent ??

Air filter , fuel filter , unplug MAF when it fails and see if it runs.

Coolant temp sensor failing ??

Unplug timing wire and see if it runs on base timing.

Is closed loop causing the problem when 02 sensor kicks in ??
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I would semi take the ICM off the table because you said you replaced the Distributor so that would mean you have a new ICM, PICKUP and oil free distributor.
You also mentioned you replaced just about all but the coil, now the coil is a overlooked item sometimes because many have a option that it's a Light On or Off thing it works or won't, but with heat they sometimes will give a weak spark but is it enough and sporadic.
Face it you pull a wire throw a spare pug on the wire and say crank it. You see a spark and yah say **** we got spark what gives why don't she run.

 

thank you for your reply, unfortunately I don't have a corvette service anywhere near me. The mechanic I deal with is only good, but the situation when it doesn't work only lasts a while and that complicates the whole thing quite a bit. I have OBD1 and no opti.

 

thanks for your reply, the ICM and coil are new, I've been changing the distributor all over and it didn't help. I will try to check pulse to injectors, but time between failure and working state is just about two minutes, sometimes even less, not much time for testing. All filters are new.

A closed loop is a good idea to look into, I hadn't thought of it until now. Most of the time, the problem occurs just before the engine warms up. How to test it? what exactly happens when switching to closed circuit?

 

Just tossing out an idea. You said the ICM is new. Did you puy a layer of the heat-sink grease under it?

 

"" what exactly happens when switching to closed circuit?""
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The O2 sensor is added to the calculation for fuel mixture. Do you have codes ??
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thank you for your reply, I will try to check signal voltage in no start state.

I have code 41

 

Clean all of your grounds and check your engine ground strap for corrosion. It (ground G104) runs from the block to behind your battery. It bolts to the engine above and just forward of the oil filter. It is hidden by the exhaust down pipe. It has 5 or 6 different ground wires attached to it and most all old corvettes need to have it cleaned even when it looks good. Use an ohm meter to read the resistance from battery ground to the engine block and see how much resistance (ohms) there is. It should be zero. You can also turn your meter to milliamps and millivolts and do the same check. I had to go into this area in the last year and with a new ground strap and a super clean connectors / block mine reads zero ohms, zero milliamps and zero millivolts.
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