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Misfire at over 200 degrees???


Starflare5

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Hey guys,

 

Ok, after solving several issues thus far with my vehicle, one new one appeared seemingly out of no where. I took the driver information computer from my old Cutlass Supreme and put it into my Regal which has a base dash and has been a world of help. Now for the issue at hand: I left the car running idle in my driveway while doing some last bit of cleaning up and brake bleeding after changing both rear brake calipers. Anyway, after a certain point, the engine started to shutter, stall, and misfire, and lit the service engine soon light. I went to check the temperature on the DIC and read 220 - 225 degrees. eventually, the car kept stalling to the point to where it wouldn't start back up. I let it cool for a little bit and it still stalled, however, this time, I managed to get into gear and able to back out of the driveway. A pecuiliar thing also occurred while it was in gear, the misfire seemed to disappear and the stalling stopped. I took it for a drive, the service engine soon light went off, and the engine cooled further because I had the A/C running. I drove around the block with no misfire or hesitation, then got back home and pulled into the driveway, put in park, and let it sit with the engine and A/C running. I turned to the guages function on the DIC to coolant temp and watched closely. The fans always seemed to kick in at around 200 degrees, however, at one point, they let the engine get up to 202 to 205. At that point, I noticed the engine starting to slightly "jump" or stutter like it had a very slight misfire, however, this wasn't enough to set off the service engine soon light. Very soon with in that time, the fans kicked back in and cooled the engine back down, at which, the misfire seemed to just fade out.

 

Any ideas on what would cause this condition?

 

Thanks,

 

Starflare5.

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How old are the plug wires? I've seen this happen before, once underhood temps rise above a certain point...particularly the wires on the firewall side.

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Do the paper clip trick, and get us the codes.

 

I'm thinking something like the MAP sensor. My old 1991 Olds Cutlass Supreme had a similar issue, and it was the MAP.

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I disagree, the AC does raise engine heat. The fan turns on which lowers the heat for a little but in general turning on and running the AC makes the engine work harder. Thus making higher engine temps

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Well, guys, thanks for your help thus far. Seems like nobody around here has an OBD 1 reader anymore and it's hard to get the codes read if there are any, so, I'm going to start with first looking to replace the MAP sensor and Coil Pack/Ignition Module for starters. If there still seems to be an issue, then I'll look to brand new AC Delco plug wires. If the issue still persist, then I'm going to take it to a GM dealer to see if they can get any info from it.

 

Thank you again guys. You've been great.

 

Starflare5.

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A paperclip can serve as an OBD-I reader. The codes are flashed in sequence through the service engine light.

 

I can make a video and post it to YouTube to demonstrate if you want. Code retrieval takes less than 5 minutes.

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Well that's very helpful... Just one question guys, will it still produce a code if the Service Engine Soon light is off? It's intermittent. Only appears when the car does that stall out routine, however, goes out when the car is actually moving.

 

Thank you again guys,

Starflare5.

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i assume this is for the 91 regal? a 3.1?

 

intermittent codes can be tricky.... if the DTC isn't being logged as current when the ignition goes off, you can end up with no DTCs being displayed via the paperclip method.

 

so, let the SES get triggered at idle, make sure it stays for a good 30 seconds or so, then key-off (or let it completely stall), wait about 10 seconds, key on, then do the paperclip method.

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Hey guys,

 

Yes it is the 1991 Buick Regal, and the paper clip, or, jumper method actually worked. I got a Code 22 - Throttle Position Sensor and a Code 34- Which in my car's case means, MAP Sensor. I'll be going to the junk yard tomorrow an looking for both, as well and getting a few things to recover from hail damage.

 

Thank you guys.

 

Starflare5.

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I decided to reproduce the issue to see if any other codes came up just in case before I go to the junk yard. 2 more appeared, Code 33 which confirms the MAP sensor, and a Code 35 Which is the Idle Air Control Valve.

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  • 2 weeks later...

Well,

 

I replaced all 3, reset the codes, yet, was able to reproduce the issue again. The end result was still just a code 22 (Throttle Position Sensor). I have been advised though that before I try to replace this with a new or another one, that I should get a few other things done to the car first, like, adjust the idle slightly higher for the time being, and then, change the injectors, for which, I've known they were bad and clogged for awhile just by the way the engine had been running for quite sometime. Then, reset the codes and fire it up again and attempt to reproduce the issue again. So, now, that's next.

 

Thanks guys,

Starflare5.

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you CANNOT adjust the idle via the idle adjustment screw on the TB and have good results. reason being you'll cause two things to happen: the base TPS voltage for 0% will be changed causing some drivability issues until it's relearned and the IAC will fight your changes by opening/closing more to maintain the idle that is commanded by the ECM, leaving you with the same idle speed and bad drivability.

 

you should have roughly .5 volts from the TPS with the throttle fully closed. anything too far beyond that in either direction will cause issues.

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Well, after replacing both the MAP and throttle position, the same error codes showed up again, but, also brought along a friend or 2. Codes 35 (idle speed) and 44 (intake vacuum leak). I think my vehicle might be a victim of the old GM 3.1 intake leak reported years ago. It doesn't seem to be leaking coolant... yet, but the vacuum leaks are present.

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After re-reading this thread I started to think Intake leak, but when I had this happen, it was the opposite of your symptoms. Would barely idle when cold, and at running temps it ran fine. Worth a shot, spray a little ether or other start fluid around that area when the vehicle is on during the poor idle condition and see if anything changes. If the idle goes up, then its sucking in the fluid which means vac leak.

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