drk1313

I just purchased a 1987 convertible - auto trans and all stock with 110K miles. While driving yesterday the SES came on and the car lost power and began stumbling. I was able to get it home OK, but it was down on power. I didn't have time to check into it right away and when I looked at it a few hours later the car ran great, no SES, no issues - until the temp gauge reach about 180 - then it all started again. I am able to duplicate this situation each time - the car runs fine until about 180 degrees. I used the jumper to pull a code 33. So far I've checked all of the connections, relays and cleaned the MAF. Same deal - car runs great then starts sputtering at about 180 degrees. I am going to review the diagnostics (I have the FSM), but I was interested to see if anyone has had a similar issue due to temperature?
Thanks!
Additional info: Yesterday was my 'maiden voyage' with the car. I bought it about a month ago but never really took it further than my street as I was waiting for plates and some decent weather. I have to assume this problem came with the car, although the previous owner never mentioned any issues.

Cliff Harris

Unplug the MAF and see how it runs that way.

drk1313

Tonight I figured I'd try flip-flopping the MAF relays behind the battery as has been suggested in some threads. I took the car for a 45 minute drive - temp was in the 200 degree range and the car ran great - no SES or limp mode issues. Could be coincidence since I may have tweaked a wire or connection by unplugging the relays and I also cleaned the plugs with electrical connector spray. I'll keep an eye on it and report back as I add more miles. I ordered 2 new relays to keep handy - but for now I may have caught a break.

drk1313

After about 100 miles of trouble-free driving the problem returned last night - and then some. It was warm here in NJ (about 85), so the temp was about 205 after going through some traffic on the way to a cruise-in. The SES/limp mode started up again, but then the car stalled and wouldn't start at all. After sitting at a major intersection for a few minutes it started and ran long enough to get me to a side street - then it was dead. It would sometimes catch, then sputter, but never idle. I had my jumper wire with me and the code 33 was the only one showing. I was only 3 miles from home and was able to get a tow quickly.

Once home the car ran for about 1 minute, but when I started to move it into the garage it stalled. It felt like a connection was bad as it was 'on or 'off' - not much in between. I went under and removed the ground bolt above the oil filter and cleaned everything up - it was covered with oil and filthy. I'm also keeping an eye on the fuel pump relay.

I read a few postings about how important the ground is with these systems, and mine was covered with 28 years of oil and grease. I did try unplugging the MAF and the MAF relay, etc. - I will perform the FSM code 33 checks, but it sure seems like a power/ground issue.

drk1313

Took the '87 around my neighborhood yesterday and the SES code 33 and limp mode started up again. It never died, but was running rough, etc.
I went through the FSM procedure line by line and it points to a bad MAF sensor (see red pen in picture). All of the steps leading up to that point went as indicated in the chart. I had to order a MAF (Duralast) - my question is this: Has anyone simply replaced the MAF and have it solve your problem? After reviewing many posts with similar issues, most include 'replaced the MAF' and the problems still return.
The part will be in on Tuesday - I'll update with the result. I'm not 100% convinced, but maybe the combination of new relays, clean grounds and finally a new MAF will do the trick.

JackDidley

On my 87 I have had MAF codes 2 times. Both times, I replaced both relays and fixed it. Never replaced the MAF sensor.

Cliff Harris

You are much more likely to have a bad connection (loose or corroded connector pins) or wiring problem than a bad MAF.

An ALDL cable and appropriate software are the only way to find out what is truly going on.

drk1313

Thanks - I replaced the MAF and I'm right back where I started. I have 2 new relays, new MAF and good grounds on the block. I'll look into the software - no use chasing any more parts. The problem still seems temperature sensitive, but sure is frustrating.

drk1313

I was able to borrow a Snap On Verus scanner tonight and I captured the following information. This is at idle (the idle varies from 1300 down to 600 - it happened to catch it at 1000. One thing I noticed is the temperature per the scanner is much higher than the dash digital gauge. Dash read 220 - scanner read 251.
I'm going to investigate these scanner numbers, but if anything jumps out to anyone please let me know



I held the gas to get the idle up around 1800 for this scan:



My Code 33 did not pop. I couldn't drive the car with the scanner connected - it kept losing the signal for some reason.

Could the coolant temp sensor be sending bad signals perhaps?

Not sure this shed any new light. I only had access to the scanner briefly.

Thanks

Cliff Harris

It looks like the coolant temperature input has a problem. The IAC counts seem high. Have you done a minimum idle adjustment:

https://www.corvetteforum.com/forums...post1570563689

drk1313

Another good call - Thanks
I went through the minimum idle steps and here are some new scans. The idle now sits nicely around 650-700 and the exhaust smells much better. I took the car for a ride (this was all done at 1am last night) and when my dash temp gauge hit 180 it went to limp mode and code 33 came back. The scanner is reading 250+ degrees. The car is not overheating.

Here's the scan with the newly adjusted base idle:




Here's a steady rev scan after base idle:





The scanner led me to fix one problem and I will do some digging on the coolant temp sensor today.

Thanks!

drk1313

I replaced the coolant temperature sensor this morning. After 50 aggressive miles in muggy 85 degree heat, so far the issue has not returned. I will be able to use the scanner to check the coolant temperature per the ECM next week. In the meantime I'll keep adding miles. The scanner info helped me sort the idle issue as well, so it was really invaluable to closing in on my problems. If it crops up again I will update the thread - Thanks for the help.

drk1313

Up to about 100 miles with no new issues. Took the Vette for a long cruise last night - it was about 75 degrees with no humidity - perfect convertible weather.
Lessons learned - Don't be tempted to 'throw parts' at the problem - try to get a scan to see what's really going on. The numbers should all relate to each other and make sense. I ordered an ALDL cable and will download OBD1 software for future use. Without this AND the factory service manual you're really going to chase your tail.
Thanks again for the responses -

Dt86

Glad that you got your problem sorted out and can now enjoy your new vette. These cars can be difficult to diagnose without a scanner since everything is computer controlled and interconnected. Many folks have done the same as you, myself included, and thrown parts at them. I got smart and bought a scanner. The FSM is good until you get an "intermittent" then the fun really begins with these cars.