sporadic service engine light
Thread Starter
Drifting
Joined: Apr 1999
Posts: 1,261
Likes: 6
From: Middletown New Jersey
sporadic service engine light
I was hoping to get some opinions from some ECM experts. I have experienced an intermittent SES light typically after I have been driving for awhile. It can last anywhere from a a couple seconds to a couple of hours. The ECM is holding no codes. I have scanned/datalogged many times previously and I use EASE software. A few days ago, the light came on when I pulled into my driveway so I got my PC and tried to scan. I was unable to connect with the ECM wjile the SES light was on. After about 30 mins the light went off and I was able to scan again. There were still no trouble codes. I had a custom dyno tune about three years ago (which I wasn't too happy with but that's another story) and the ECM was replaced with a rebuilt one about 4 years ago.
I haven't removed the ECM yet but does this sound like the ECM is crapping out or should I look somewhere else.
Thanks in advance
I haven't removed the ECM yet but does this sound like the ECM is crapping out or should I look somewhere else.
Thanks in advance
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
How does the car run when the SES light comes on? Same or worse or ? It could be the beginning of the end for the ECM, but if it is running OK it could also be another sensor or some other intermittent problem, I would wait until it gets worse, but if you cannot connect to the ALDL when it's on it sounds like the ECM. OMT, how does your instant/average fuel economy readout look? Esp. when the SES is on.
Thread Starter
Drifting
Joined: Apr 1999
Posts: 1,261
Likes: 6
From: Middletown New Jersey
The car runs terribly when the light comes on. It will barely stay running. I have always believedthat the reason for that in my case is because the limp home mode wasn't designed to handle my modded motor.
The only other thing that I think points to the ECM is that I have high BLM's and INT's (160 BLM, 135 INT at idle) but when I have had the exhaust put on the sniffer, it had high HC's and it smells a little rich. My mechanic has looked for vacuum leaks but hasn't found anything. I had my heated O2 replaced with a new one about a month ago but it didn't help. I get plenty of O2 sensor crosscounts so I don't think that is the problem.
One thing I was wondering though. I have the C68 auto climate control. For the last few years, the air blows out of a few different vents no matter what setting I use. I realize that engine vacuum is used to control which ducts the air flows thru. If the problem I was having with the A/C had to do with bad vac. lines, would that also cause a the symptons with the high BLM, INT that I described above? I haven't checked these vac lines because they are a major pain to get at.
The only other thing that I think points to the ECM is that I have high BLM's and INT's (160 BLM, 135 INT at idle) but when I have had the exhaust put on the sniffer, it had high HC's and it smells a little rich. My mechanic has looked for vacuum leaks but hasn't found anything. I had my heated O2 replaced with a new one about a month ago but it didn't help. I get plenty of O2 sensor crosscounts so I don't think that is the problem.
One thing I was wondering though. I have the C68 auto climate control. For the last few years, the air blows out of a few different vents no matter what setting I use. I realize that engine vacuum is used to control which ducts the air flows thru. If the problem I was having with the A/C had to do with bad vac. lines, would that also cause a the symptons with the high BLM, INT that I described above? I haven't checked these vac lines because they are a major pain to get at.
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Even a stock motor runs pretty bad in limp home mode, I had an intermittent failure like you are having and it was the ECM. I would replace it and if it does not help your fueling too, then start investigating vacuum.
Mark
Mark
Thread Starter
Drifting
Joined: Apr 1999
Posts: 1,261
Likes: 6
From: Middletown New Jersey
Thanks gbody5, I appreciate your thoughts.
I didn't really notice the inst/avg fuel economy when i was having problems. I wasn't aware hat it changed when it went into limp home mode.
I didn't really notice the inst/avg fuel economy when i was having problems. I wasn't aware hat it changed when it went into limp home mode.
Drifting
Joined: Nov 2001
Posts: 1,783
Likes: 2
From: Latham NY
Originally Posted by GlennS87
For the last few years, the air blows out of a few different vents no matter what setting I use. I realize that engine vacuum is used to control which ducts the air flows thru. If the problem I was having with the A/C had to do with bad vac. lines, would that also cause a the symptons with the high BLM, INT that I described above? I haven't checked these vac lines because they are a major pain to get at.
There is a vacuum check valve on the back of the plenum with two ports, one to the vents and the other to the cruise control. There are also fragile hard plactic vacuum lines under the plenum that can crack and leak.
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