M50 stumbling, CEL flashing (codes pulled)............

[Dave M]

1991 M50 e34, symptoms are as follows:

After running for a few minutes, CEL flashes, either stays on or disappears shortly after. When the CEL flashes, the engine stumbles just slightly and it feels like the ignition/throttle adjusts quickly (slight surging/hesitation). No strong correlation with any particular vehicle speed or engine speed. I do NOT have a catalytic converter on the vehicle. The vehicle ran dry (fuel) last summer and the sending unit/fuel gauge has been F-cked ever since.

Just pulled some codes and the description from Bentley is below. After pulling these two codes I stomped once more and got a string of a long CEL followed by a short CEL (_____ _ _____ _ ______ _ ______ _). Does this pattern indicate anything??

So, I haven't checked the O2 sensor or my fuel pressure, but I wondering if anyone has any advice or similar experience. Would a bad O2 sensor cause a stumble on an engine at operating temp??

Thanks in advance for any input,

Dave
__________________________________________________ ________________________

1221 Lambda (O2) Sensor 1

This code is stored when the engine temperature is >70C and
the Oxygen Sensor value is out of range or not present. Check
the Oxygen Sensor wiring and the operation of the sensor. The
value should fluctuate between 0.02 and 0.85V. Slow
fluctuation indicates a polluted Oxygen sensor and negative
values indicate a damaged sensor. Note: Cars without
Catalytic Convertors will incorrectly store this code.

1222 Lambda Control 1

This code is stored when the DME detects excessive
deviations in the air-fuel mixture (too rich or too lean) for longer
than 10 seconds. Possible causes: Fuel tank ran empty,
Incorrect Fuel Pressure, Injector valve defective or coked,
Engine Temperature Sensor defective, Secondary air leak,
Fuel evaporation control system defective, Air Flow Meter
defective and/or the combustion is being disturbed by
mechanical failure (Spark plugs,, compression,
intake/exhaust valves, ...etc.)

[alex 1993 525i auto]

Funny to suggest something to a 2 Grand Master,

Did you check for a vacuum leak, vacuum lines, intake manifold gaskets, AFM? On my car that was the problem which triggered the O2 sensor CEL light (at that time I didn't know much about the car, it was a long way before it was solved by replacing all of those in the end).

[whiskychaser]

Just so I am clear, you have the M50NV with 3.1 DME (no cat/no O2 sensor)?
If so, I have the same engine and a similar problem though mine is more of a niggle. From cold mine idles fine at about 900rpm. After a few minutes it drops to around 700 rpm which is normal for my auto. Occasionally, the engine rpm will dip a tad then quickly resume. It is only about half a needle's width. I dont have the CEL but I know I have no codes stored or live. I've checked the usual suspects as I am sure you have. Did you actually remove the coolant and air temp sensors and stick them in a pan of water with a thermometer?

[Dave M]

Funny to suggest something to a 2 Grand Master,

Did you check for a vacuum leak, vacuum lines, intake manifold gaskets, AFM? On my car that was the problem which triggered the O2 sensor CEL light (at that time I didn't know much about the car, it was a long way before it was solved by replacing all of those in the end).

Alex,

Sorry for not noting, but I doubt it has vacuum leaks. The engine has been in an out of the car a couple of times in the past and all suspect bits were replaced. However, I will give it a once over to rule it out.

Thanks for your reponse,

Dave

[Dave M]

Just so I am clear, you have the M50NV with 3.1 DME (no cat/no O2 sensor)?
If so, I have the same engine and a similar problem though mine is more of a niggle. From cold mine idles fine at about 900rpm. After a few minutes it drops to around 700 rpm which is normal for my auto. Occasionally, the engine rpm will dip a tad then quickly resume. It is only about half a needle's width. I dont have the CEL but I know I have no codes stored or live. I've checked the usual suspects as I am sure you have. Did you actually remove the coolant and air temp sensors and stick them in a pan of water with a thermometer?

Whiskey,

Its a NV M50, no Cat, but I do have an O2 in the 'stock' location. Cat was removed by previous owner, but O2 retained. I've been lazy and haven't tested all potential sources (temp sensors, TPS, fuel pressure etc.). Mine does sound a bit more serous than yours, although mine is still quite drivable, more of an anoyance. It will get resolved with time, but I was just wondering if anyone had a shortcut :D

Thanks again,

Dave

[whiskychaser]

Nobody else would even notice it. I get about 33-34 mpg on a run but I think it is running a tad rich. Mind you, that is imperial gallons. I'm thinking maybe lazy injector(s)? Yes its just a niggle. It a bit like Charlie Croker in the Italian Job when he says one of the carbs on the Aston may need a little more air:D

[Tiger]

Check vacuum leak first. I suspect your MAF/AFM is bad. Don't forget your intake manifold for leak... use carb cleaner or something similar to check for leak.