I am the proud owner of a 1991 Cadillac Sedan Deville with 199,000 mi on her, but I am getting a little worried she won't make 200,000. A few months ago she started stalling on me when I would be coasting to a stop (pulling into a parking space for example). I figured it was the ISC but I didn't have the $ to change it so I adjusted the ISC pushrod by threading it out until the car would idle. A couple of weeks later I was taking a 2000mi trip so I took her in for service at a GM dealer. Dealership ran diagnostic and said she was good to go. Now that I have made the trip the car is backfiring when I start it. I tried to run the onboard diagnostic, but all I get on the climate control screen are ----- and the "off" and "hi" designations are highlighted, but there are messages being displayed on the Electronic Fuel Monitor. I can't figure out what they mean, and they don't scroll by, I found that I could scroll through them by pushing the HI button on climate control side.
I already tried dry gas to try to get any moisture out of my fuel system, but it is still backfiring and running rough at idle. Any help would be greatly appreciated. Thanks
I think I wrote too much last time without saying what I meant. The car only backfires through the exhaust when idling, and only before I put it into gear. After I put the car into gear it runs fine, that is until I get to a stop light, then it starts to run kinda rough and it acts like it wants to stall. I was reading a post on another sight that talked about a similar problem, and the mechanic mentioned that the problem may be the result of a bad alternator. The mechanic was saying that when a Cadillac's alternator is not putting out sufficient voltage at idle the computer automatically advances the timing to increase the voltage output. After I read this I had my alternator checked and sure enough the voltage output is low. I am going to change the alternator tomorrow and post my results.
Thanks to anyone who has read this and especially NODIH for writing the first reply to try to help.
You may be onto the problem if the voltage is low and the ECM is not reading out codes on the climate control panel. If the voltage gets low the PCM will actually drop out and stop functioning leaving the system operating in a back-up or limp home mode. The PCM does not advance the timing or anything like that to try and increase the voltage.....don't know where that idea came from. But the backfiring could come from the very basic limp home mode of operation since the spark is actually not advancing at all in the back up mode.
One quick way to check this out is to put a battery charger on the battery and charge it up completely and see if the car acts fine for the first few minutes of operation. The engine and system should operate fine off the battery for several minutes but the battery will quickly be depleted to the voltage level the generator is putting out and the misfiring will return.
Thanks alot for the advice bbob, that helps alot. When I made this post I was really hoping you'd have a suggestion for me. I don't know much about PCM's and what they do and do not control, so what that "mechanic" said seemed reasonable enough to me. I really appreciate your second opinion though, it is much easier to follow and explained much better. Unfortunately I don't have access to a battery charger where I am living now, so I will just have to swap out the alternator and pray it works out. I appreciate the help, thanks again, Dave.
bbob, thanks again for the help, the car has about 200K on it as I mentioned before, and I know for a fact that the alternator has never been changed. Knowing this I figured a new alternator couldn't hurt anyting so I went ahead and replaced it, it made a world of difference. I am pretty sure you were right about the PCM not functioning properly because after I replaced the alternator I checked the OBD again and it still displayed on the fuel data center screen, but it displayed an E52 code which is the PCM reset code. Not only that, now when I start the car there is no backfiring, and when I come to a stop the car seems to idle just fine. All your help is much appreciated.
It's gotten MUCH worse - I was driving to work this morning and the car completely died on me - going down a hill, the stop engine/oil light came on. I've had it come on more and more often as the car is near stalling on the road, so I gave it gas and it seemed to fight with itself to keep running. It ended up dying completely. I pulled into a left turn lane and tried to start it again, and I got a moderately loud backfire. Not sure where it came from, but a bunch of black soot came through my window shortly after that.
I've noticed the lights dimming when it almost dies, and my climate control and fuel centers don't stay on, although I can see them for a fraction of a second when the car first turns on.
Could an alternator be my problem? Or maybe a bad ground? I don't think an 85 4.1 has timing advance. This is the worst day it could possibly die, my entire family went out of town on a camping trip and I can't get to work.