kzetmeir

I changed the sensors on my front brakes and the oil and filter on my '89 928S4 115k miles.

The brake light is still on ... I'll have to track that down.

More importantly, when I restarted the car, it runs great for 20 seconds then immediately stalls big time. Does this every time I start it.

Have I knocked some wiring loose?

Michael Robinson

I had a similar problem on my 86' 928s last year. Turns out I could get the car started and road bound, but every time I pushed the clutch in I would have to fight to keep the revs up or it would stall on me. Did it for three days and I left it for two days and tried it again. I wasn't even able to get it fired. I had it taken to the shop and they took a good look and identified that it was the O2 sensor and it had fouled the spark plugs. I had 125K on it when it went bad.
I would guess that your 89' has a similar problem. I would try a new O2 sensor and see how that goes. Your car has 115K and the 02 sensor should be replaced by now so it wouldn't be a bad investment. Also change out your spark plugs when you change the 02 Sensor. I would say this might be your problem. Give it a shot it won't hurt to change it anyway. This job can easliy be done in at home. You can order a O2 sensor and plugs at 928 International (www.928intl.com)
Let me know how things work out.

Michael Robinson
86'928s Blk/Blk
87' 928s4 Red/Blk

kzetmeir

Before the oil change and replacement of brake sensors ... the car was running great.

The car has no problem in starting now and runs very smoothly for 15-20 seconds at 600 rpm.

Then it immediately gets rough, probably kicks out one side of the fuel injection as it acts like its running on 4 cylinders and stalls.

I disconnected the battery to reset the computer.

Seems a bit too coincidental with the work I did for it to be an O2 sensor and it runs too smooth on start up for it to be plugs.

Your suggestions are good regarding the regular maintenance on the sensor and plugs.

Thanks.

Greggg

Have you had the "brains " tested? I've read that after some modifications they act up. This is strictly a shot in the dark...

Moss928

Most likely; the timing of events is coincidental. 928's can be very mischievous. Problems appear out of thin air, and often without warning.

A couple of things to check: 02 sensor, distributer cap/wires and the coil.

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WallyP

Starting in '89, the 928 has an "Ignition Monitoring Circuit".

There is a temp sensor in each exhaust manifold. If one of these sensors sees (or get a false indication of) low exhaust temp, the system assumes that the ignition system for that side has failed. In order to prevent cat fires from pumping unburned fuel into the cat, the system shouts down the injection on that side.

Pull the cover over the ECUs on the right kick panel. Look on the forward end of the ECUs and find a clear plastic box. Crank the engine.

If a red LED lights up in the box, the system thinks that the right ignition system is down.

If a green LED lights up in the box, the system thinks that the left ignition system is down.

Did you disturb the exhaust temp sensor when you changed the oil?

Is one of the ignition systems dying?

kzetmeir

You guys are great ... thanks for all the suggestions.

I thought I'd found it. The car ran for a couple of blocks ... then cut out again.

To get that far, and I don't know if this helped, I pressed hard on the coil wires on the bottoms of the distributors. I also tapped lightly on the sensor on top of the intake manifold.

Alas ... came back to the same problem. So I took Wally's advice and pulled back the ECU cover. Sure enough, the green light comes on indicating a problem on the left side.

I've looked for the temp sensor on the exhaust manifold as best I can from a floor dolly and trouble light ... but am not finding the temp sensor. Can you help me locate this bugger?

Also ... is there an online cutaway showing the locations of all the various components?

Thanks

WallyP

Remove the left coil wire. Inspect it carefully from end to end in a good light. Replace it if you find any tiny puncture holes. Otherwise, clean the sockets on both ends and the ends of the wire, and reinstall it. Route it away from any metal id possible.

kzetmeir

I removed the coil cable which is only 2-3 years old, took it into the sunlight with a magnifying glass ...

Couldn't find a thing ... no pin holes, no contact contamination.

I put it back in ... started up ... no change other than it will idle until put under load ... then the green led comes on and it stalls.

WallyP

There are two possibilities:
The left ignition system is failing, and the monitoring system is functioning perfectly.
The ignition system is fine, and the monitoring system is faulty.

Find an inductive-pickup timing light. Crank the engine, and check the left coil wire for voltage using the light. If there is strong fire on the coil wire, concentrate on the monitoring system.

To find the left exhaust temp sensor:

From under the car, look at the inner bottom of the exhaust manifold, just forward of the attaching flange for the downpipe - just between the manifold and the engine block.

Check the attached wire.

Sometimes you can cure a problem by loosening the sensor and rotating it 90 deg.