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Re: Continuing issues (archive)

[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]

Posted by Keith '88 750il on August 10, 2001 at 19:23:37:

In Reply to: Re: Continuing issues posted by David F on August 10, 2001 at 12:40:07:

David,
Thanks for the information about the Check engine light for early 750's. I was going nuts trying to figure out how to retrieve the codes using the peddle.

I was referring to the sensors at the back of the manifolds. Found your information very helpful (although I lost one of the clips in the process). Looks as if one of the sensors may be bad.

Thanks for the reminder about the coil. I already replaced one (which was definetly bad) but forgot to compare the readings on the new one to the other old one. I will do that tomorrow.

I suspected as much about the Oxygen sensor heater relay, but wasn't sure. Just looking for anything that could be the problem. I have sense reinstalled it in the car.

Thanks!
Keith - '88 750il

First of all, most (if not all) early US 750's do not have a functioning 'check engine' light. Therefore the accelerator pedal method of retrieving codes does not work.

With that said, I would check for a faulty ignition coil. Coils typically show signs of failure after they get warm/hot.

Removing the oxygen sensor heater relay will have absolutely no effect on your problem. The heater only serves to speed up the normal operation of the oxygen sensor. Once the car is at operating temperature the heating portion of the sensor is not needed.

I have no idea what red wire you are talking about, sorry.

As for the "air intake sensor" if you are talking about the MAF, then just turn the round connector counterclockwise until it comes off. If you are talking about the air temp sensors in the back of the intake manifolds, then press wire clip and pull straight off. To test for voltage while connected, you must peel back rubber boot and back probe the correct pins.

Again, rich condition after warm-up suggests a weak coil not producing adequate spark to one side of the engine. Vacuum leaks usually result in a lean mixture. I suppose it could also be a faulty MAF not sensing the proper amount of air entering the intake. Good luck.


I have been trying to get my 750 to run right for the past couple of months. I'm not able to devote a lot of time during the day, so I'm working rather slowly.

At this time the car runs great when started and after letting it idle for a seemingly unlimited amount of time. Even after taking to the road all the power is there and idle is normal until the car is driven for about 15 minutes or more. Then the idle gets very rough and power is lost unless the peddle is pressed to about the 3/4 full position, at which time the engine will clear up and power comes on. When idling, it gets rough and the exhaust becomes very rich and dark.

I have begun to suspect that something on the engine is not acting correctly at temperature. I removed the Oxygen sensor heater relay and the core seems to run much better. Actually I'm not fully sure if the car is running better tonight because it is cooler outside, or because I have removed the Oxygen sensor heater relay.

Does anyone have any thoughts on this?

Also, Does anyone know how to remove the connector for the Air Intake sensor? I have never removed it, and don't want to break it. How do you check for 5 volts between the supply voltage wire and ground while the harness is connected? Or are you supposed to disconnect the harness?

When I look in the Aux Relay Panel there is a red wire that appears to have been cut. Does anyone know what this wire goes to?

Also, when the engine is running bad, I would expect to get a check engine or EML light. I don't and wonder if the engine management system is recognizing that the engine is not running correctly. I have tried to get the codes from the OBC computer by pressing the gas peddle 5 times, but this has not affect. Can anyone tell me why I can't get codes from my OBC?

Your help is greatly appreciated!

Keith '88 750il






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