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Re: Intermittent stalling on 535i. Motronic? (archive)

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Posted by Richard Beaver on November 24, 2000 at 09:55:01:

In Reply to: Intermittent stalling on 535i. Motronic? posted by RonW on November 18, 2000 at 22:00:02:


My '86 535 just developed an intermittent stall (every 2 hours or so). Can anyone offer some insight? Here are two typical scenarios, followed by some additional diagnostic info:

-I'm coasting down a hill. The engine dies, and the idiot lights turn on. I shift to 5th gear, release the clutch pedal, and it restarts instantly.

-I'm driving normally. The car suddenly "engine brakes." I wait a few seconds for it to restart, but it never does. I hit the clutch pedal, the engine dies, the idiot lights turn on, I release the clutch pedal, and it restarts instantly.

Apparently the engine has to officially stop before it will restart.

Here is some additional diagnostic info:

When the engine dies with the transmission in gear, the tachometer continues to show the rpms. With a traditional tach, that would mean there was still spark, but I don't know if the e28 tach works off the coil.

When the engine dies with the transmission in gear, the fuel economy gauge registers maximum economy, even if I (or the cruise control) floor the accelerator. This tells me that the Motronic unit has decided not to actuate the fuel injectors, as opposed to the problem being a faulty fuel pump or pump relay.

I've noticed that turning on various lights causes the temp. gauge to flicker a little, typically causing it to increase its reading. Sometimes it flickers for no apparent reason. The fuel gauge does not flicker. I'm guessing this is a ground problem. Could this be related to the stalling problem?

The car normally runs well, and idles steadily at 700 rpm.

Thanks in advance.

- Ron
I don't know if you've resolved your problem yet.

I was cruising on the M535i site and found the following . Since the M535i is the same car with all the M5 regalia this could be causing yur problem.

{Several chronic problems show up as 'cutting out' at any speed, frequently the 'main' relay, sometimes the fuel pump relay, sometimes the position or timing sensors. Connections to the _underside_ of Fuse 6 can corrode and heat up.}

I can answer your question about how the Montronic gets RPM sensing for the tach.

The Montronic unit get's this from one of 2 sensor's mounted on the lower right rear of the block. One is the reference sensor for TDC the other reads the teeth in the flywheel and provides the RPM data to the ECU.

If you don't have a Bently manual you should get one. Very in depth information on the Fuel Injection system, with great troubleshooting info.

Good Luck.

Richard '83 533i (181k)




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