Re: Another Stumbling E-28 (archive)

At full throttle the O2 sensor isn't considered since the engine should be full rich at that point. But it can be a useful measurement tool so plug a meter on it and install it in the cabin so you can monitor its signal. These types of symptoms happen either when the engine isn't receiving enough fuel or it may be receiving sufficient fuel but the engine isn't burning it because of insufficient spark. Either way you'll probably find that the engine is running way too lean as indicated by the o2 sensor voltage. I've had both problems, insufficient fuel due to a clogged fuel filter and at another time insufficient spark due to an oil fouled distributor cap when my cam seal finally let go. The latter was more noticeable on wet days. Therefore, any or all of the posts below should be considered.

demet

Well, up until yesterday, the '88 535i was running its usual totally fine self. Getting ready to cross the Bay Bridge (MD) at a steady 65 or so, it just started stumbling, losing power, and slowing down. An exit was just there, so I pulled off and it hiccuped a few times, cleared itself, and no more problem.

Today, it's worse. Symptoms. At steady 60-70 in 5th, any pressure on accelerator causes it to stumble and/or bog. Increased gas pedal causes more stumbling, until I reach the point where it's floored, and it just almost loses all power and starts to coast down, albeit without dying. It's like a switch when the pedal hits the floor, causing it to totally bog. Same symptoms in 4th at higher rpm. Back off the floor and it returns to life, but only for steady speed, no accel.

Put it in neutral, and blipped it to 5K a few times, at first it would not blip, then something cleared and it blipped normally. Drove home another 10 miles, everything OK. Now worried.

Anyone got any ideas?

Rgds,
Chris Whitney
'88 535i, 147K

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