How do I begin diagnosis?

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Jul 24, 2001 | 11:39 AM

Narnian

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From: Sacramento, CA USA

My motor is only eight months old, and it was running smooth as can be until I took a long trip about three weeks ago. Over a thirty minute period it went from riding smooth to severely rough, and I lost a great deal of power. The check engine light came on and I flashed the ALDC to get code 32.

After going through the diagnostics and checking on this board I swapped out the EGR valve. The valve was definately bad. However, that didn't fix the problem. The car is still running rough and doesn't have the power it should.

Can anyone tell me how to start diagnosing it?

86 Corvette, mostly L98

Jul 24, 2001 | 11:59 AM

89C4L98

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From: New Jersey

Did you clear the codes and drive and check for more? Do you have good fuel pressure? How are your spark plugs, distributor cap? basically do you have a small miss like a tune up could cure. Or do you have a BAD problem?

Jul 24, 2001 | 12:24 PM

Narnian

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From: Sacramento, CA USA

I cleared the codes and checked for more (none yet, but I only drove it two miles)

I haven't checked fuel pressure - How do you check the fuel pressure?

Could the spark plugs or Distributor cap go bad like that? I've never had swift deterioration out of those before. If it can, I'll go pull them out and inspect them.

Jul 24, 2001 | 01:10 PM

vettenuts

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From: At the beach in little Rhody

I will admit to not being totally familiar with the pre-90 EGR system, but there is more to it then just the EGR valve itself. Prior to moving on and changing parts, check the control system for the EGR. Also, reset the ECM and then drive the car. Then re-check for codes to see if 32 is still coming up. Sounds like you might still have an EGR problem.

Jul 24, 2001 | 05:49 PM

Narnian

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From: Sacramento, CA USA

I basically followed the diagnostic chart for code 32. It might be a problem with the ECM, but it hasn't given me any more error codes. There may still be a vacuum leak to the EGR, but that should force it closed, which I think would only result in me failing emissions - it should run OK.

I just drove it for twenty miles to see if it would give me more codes. Before I swapped the valve it was just plain terrible rough. Now it feels more like it's missing. Checking the plugs might be a good next step, so I'll stop at the parts store and pick up new plugs tonight. Is it possible for a bad EGR valve to cause a plug to foul or burn?

Jul 25, 2001 | 12:00 PM

Rick86

Burning Brakes

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Narnian, I'm going through a similar problem (diagnosing) I know it is a PIA, but this is what I've learned about the EGR: If the egr system is good, it will not open below 150 degree coolent temps, WOT, or idle, but will open at rpms over 900. Does the engine run better at higher rpms? If so then start checking for a vacum leak. Try retorquing your intake bolts, my intake developed a leak two months after rebuild. Good luck

Jul 25, 2001 | 01:47 PM

Team Owner

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From: Trying to get back to Bokeelia, FLA-USA

St. Jude Donor '04-'05-'06, '15

egr vacuum switch on the rear of the intake?

I though i had a bad egr vavle too with my 85...ended up being that vacuum switch that is mounted on the rear of the intake left of the distro..
theres a process of testing it...i forgot was it was..but its in the haynes manual..

Jul 25, 2001 | 03:50 PM

Rick86

Burning Brakes

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JD, I think your talking about the egr temp switch (vacum switch is located up front of intake near thermostat) anyway the switch by the distributor attached to the egr tube is the temperature switch. It should have 12 volts pwr when egr closed. When egr opens hot air grounds the temp switch, which lets the ECM know the egr has opened.