Help with Erratic Ignition & Check Engine Light

[510man]

Thanks for the help.

Yes

So where is the fuse link on a vert since the battery is in the front?

The code associated with the CEL will remain in the DME until cleared or the DME reset by removing power.

Understand but the CEL went out. Has not come back on since nor has the problem reappeared. Still want to find the problem as I don't view the vehicle as reliable as it is.

The movement of the temperature gauge is interesting, but probably an artifact of the cut outs. The MPG gauge going to 40 indicates that the DME isn't producing firing pulses for the injectors. In conjunction with cut outs that is most commonly caused by a problem with the timing reference data. Though one usually sees the tachometer react. The DME does include a rev limiter that is triggered by the engine speed as reported by the timing reference data.

So an interrupt or weak reference data could make the tach bounce. Typically tachs I've seen bounce due to ignition cutout go all the way back to zero when they bounce. This was doing that. It's stopped now.

With what has been done my suspect would be the engine harness. The coax in it for the CPS data may be degraded. A problem there will cause exactly the problems described.

Oh yeah. If original, the engine harness on this car does not have C191.

The engine harness is original. If I replace it, what am I replacing? Is there a part number? I assume there are many things that plug into the engine harness. Start at point A and work your way to the end of all the various splits.

[510man]

Sorry for the reporting delay. I don't have a lot of time to stay on this project. I'm back to it for now. I've posted this problem on several boards and have received several things to checkout.

One suggestion was a possible grounding problem through the gauge cluster screws. I repaired the ODO gears. I cleaned the electrical connectors on the cluster and ensured all the screws are tight. Mine all appear to tighten into plastic (early VDO cluster) so I'm not sure how that ties to a possible grounding problem. Regardless, it's been checked.

I removed the negative battery terminal to remove the gauge cluster. That will reset the OBDI codes. We'll see if the problem comes back.

Separately, I ordered new main, fuel and O2 relays. Mine are all original stamped 2/87. the shop that looked at the car recommended I change them. Will snap those in when they arrive. It would be nice if it was the main relay getting quirky!!

Removed and cleaned the ECU ground post. I looked clean but I removed, cleaned and re-tightened it anyway.

I found the fuselink. Several people suggested this as a possible problem. It's in the harness covered with some shrinkwarp-like loom. If the problem comes back, I'll remove the insulation to where I can see if the link is corroded. I read elsewhere that some people bypass the link using a 50A car stereo fuse holder. Carry an extra fuse and this potential problem is solved.

Will drive the car for the next few days to see if it has a reoccurrence and report back. Sometimes it will act up within 10 minutes while other times it will drive fine for days before having a problem.

[603Racing]

The c191 is about 6" below the throttle body. It's a round connector that mounts to a bracket. The connector unscrews off the bottom. You should open it an look for corrosion. My car would sputter, not rev high, MPG gauge going to 40... all when the c191 was corroded. You can clean it and that should help for a while. Ideally, you should replace it. There are threads on the c191 on this board.

[510man]

Thanks. Nothing like that under the manifold on this car. Somebody on one board said my '87 does not have that connector under the manifold.

[510man]

Relays replaced and SI batteries replaced. Gauge screws are all tight. Drove six miles and had the same problem. Disconnected the battery to reset the codes and the car drove home fine. Had one significant miss while sitting at a traffic light but it recovered with no CEL.

I'm off to the fuse link and temp senders now. If it's neither of those, I'm to the engine harness.

[510man]

Ding, ding ding!!! I think we may have a winner. Replaced the blue temp sensor that feeds the DME. Car runs great. I drove it 40 miles without issue. Previously it would fail in six miles. Progress!! We'll see what happens over the next few days.

If this ends up being the problem, it would have been discovered long ago if BMW didn't out engineer itself by using multiple water temp sensors. If they only used one, the temp gauge would read incorrectly, I'd replace the sensor to fix the gauge, and I'd fix the DME data issue at the same time. Lots of time and money wasted if this is it.

[Mab1957]

Was the blue temp sensor the cause?

My '92 e30 vert exhibited the same symptoms for the first time this afternoon. I drove it almost 200mi yesterday and for some local errands today with no issues. I park in the driveway, then within a couple of hours upon restart the Check Engine Light (CEL) comes on with a bit of a chime corresponding to its blinking, it runs rough, won't run well at higher rpm, the gauge needles are jumping (mpg covers the range) and two upper right OBC lamps twinkle insynch with the CEL light/chime. After I shut the car off I could still hear the chime and relay making behind the cluster so I disconnected the battery. It has recently been running the battery to dead, so one of the comments above about alternator failure will cause me to check that.

I'd love to hear your successful conclusion and start my trouble shooting there.

[510man]

Following up on this lengthy thread.

I replaced the TPS in this car and it seems to have resolved the problem. I've been here before only for it to come back so I'm hesitant to say it's fixed.

The TPS tested good with an ohm meter. However, the car would not go into stomp mode. I replaced the switch in my pursuit to fix this problem. Really just another guess trying to find what's wrong. Since replacing the TPS, the car now goes into stomp mode and the problem has not come back in several hundred miles of driving.

I also replaced the ignition wires. They were aged but I'm not sure they were bad. It did, however, smooth the idle out a bit so probably worth doing. I replaced the wires several weeks after the TPS in an effort to isolate the fix.

It's a very intermittent problem so it could still come back. Time will tell. If I don't post further, assume it is finally resolved by replacing the TPS.

[510man]

I've received several PMs on this thread. It was the Throttle Position Switch. It tested good and was one of the first things I tested. A BMW mechanic friend said replace it. I did and the problem has not returned since the Feb 2014 post. BTW, the TPS I removed still tests good. Go figure.