1985 C4 4+3. ALL the EGR components have been replaced with new ones. Even the CTS (coolant temp sensor) for the ECM was replaced because I understand it sends temperature readings to the ECM for EGR operation and many other engine functions. The engine idles smooth and runs just fine. BUT----sometimes the CHECK ENGINE light indicating EGR failure comes on 2 seconds after a cold engine start. It will stay illuminated until the engine reaches over 135 degrees and I turn the ignition off. When I restart it, the light doesn't come back on and won't come back on unless the engine is stone cold again. And then not always. I don't have a catalytic convertor as the exhaust is modified. Any ideas what could be causing this?

 

I had the exact same issue last month. It was really getting on my nerves. I replaced my egr solenoid connector(mine was cracked) then cleaned the 2 egr
diverter and solenoid connectors with electric cleaner, checked that egr vacuum hoses were all tight, unplugged battery to reset faults and has not came on since.
Good Luck

 

Why do you think this only occurs on a cold engine? And why it doesn't happen on every cold start up? In simple terms, what do I now have to do to correct this situation?

 

It occurs as stated above when you start up the ecm checks for a signal your connectors are probably dirty
It does not check for a signal when warm.
Make sure your egr solenoid connector is clean and working.
Make sure your diverter valve connectors are clean and tight
Make sure your vacuum hoses are nice and tight
Make sure the egr tempature connector is clean and tight
Disconnect battery for 30 seconds and reconnect and start up.
Spray then with ecectric cleaner not wd40.

 

have you replaced the egr temp sensor?
you can always have the error 32 programmed out.
Www.tunedperformance.org

 

I had replaced EGR valve and temp sensor about 6 months ago,my problem was faulty connectors.

 

Do you mean the wire with the sensor attached to the end of it that screws into the EGR valve?

 

When the EGR goes "bad" the corrugated tube from the EGR valve to the exhaust system gets very, very hot, mine melted the velcro on the cover and burned it a bit. The wires on my engine near the EGR tube were bare from the surrounding heat, it would be easy to short out that way causing the code. Make sure the wires have a good insulation on them to avoid problems.

A Bad EGR will cause your combustion temperature to go above the normal limits and your engine will start pinging. When the engine is Hot the cooler air injected by the EGR will reduce the operating temperature of the engine and keep it running without detonation.

My EGR failure "started" at the EGR Vacuum Solenoid and compounded itself from there. I did not notice anything until I took the car for it emissions testing and it failed due to a High NOX level caused by a bad EGR. It took several days to clean up the damage and the carbon left behind.

If you have a Corvette that NEEDS premium fuel to keep it from pinging check your EGR as it is probably not working or the ignition timing is off. The C4's like my 1988 Coupe have 9.5-1 Compression ratio and with Aluminum heads the engine should run just fine on 87 octane fuel. I have no pinging on my 103,000 mile old C4.

Removal of the EGR is a "bad idea" and would require a new chip programmed specifically to remove the EGR function. Don't just unplug it and think it is "Disabled". Removal of the EGR is not good for the car's Performance or efficiency. The engine will run hotter and ping more without the EGR working.

There are some great suggestions above in this post, follow through and let us know what the problem was and how it was resolved!

Best regards,
Chris

 

Yes, it is a pain. I would need to remove the plenum to make the adjustment. You can't get at the wire and pin otherwise.

 

I cleaned the electrical connections today with a cold engine. I started it and got no check engine light! I hope it's fixed.😊

 

Ok...….The CHECK ENGINE light came on again at cold start up. I left the engine running and unplugged the EGR temperature sensor. (The sensor that screws into the EGR valve and plugs into the wiring at the back of the engine on the passenger side). Once unplugged the CHECK ENGINE light stayed on. As soon as I plugged it back together, I heard a "click" and the CHECK ENGINE light went out. I shut the engine off and let it go completely back to cold. I started it up again and the same CHECK ENGINE scenario started again. Unplugged it, plugged it back in and the light went out again. I ordered a new EGR solenoid connector plug as the old one doesn't snap completely onto the solenoid. The little black tab that locks the plug onto the solenoid won't lock them together. I replaced the EGR solenoid with a new one awhile back and the old plug fit, but it never "clicked" or locked together correctly. Problem here?

 

This temperature sensor sounds more and more like the problem for sure. I'm considering running a line with a hidden switch and splicing it into the temperature sensor wire and just leaving it switched off at cold start up and switching it back on once the engine is warmed up. Do you think that will work? Does the sensor need to be connected after the engine warms up for any reason?

 

This (hidden) switch idea sounds a heck of a lot easier than removing the plenum and trying to manually adjust that pin that was supposed to be factory set. If I ever do have to remove the plenum for something more important, then I'd try to adjust that pin at that time. All this just because I don't want to be staring at a CHECK ENGINE light for no real reason.