BMW Repair: Fuel Pumping, hairline cracks, crank sensor

Question
My 520i 1981 model(with the the fuel distributor) seems to suffer momentary fuel cut-off during driving.The symptom happens after engine has warmed up and occurs in 4-5 seconds span. Mechanics in my area analyse that it is a fuel feed system malfunction either 1) Primary Pump failure (I replaced about 1 yr ago) 2) Fuel ditributor failure (not replaced yet) 3) Crank sensor malfunction (not replaced). Yr advice is seeked before I proceed for repairs. Thanx

Answer
Hi there,

One of the most common causes of this type of behaviour in the early motronic BMW's was due to dodgy connections on the Coolant temp sensor (at the front of the block near the thermostat housing). But as this appears to be an electrical fault you should take the opportunity to clean as many electrical contacts as possible, especially on an older car. I would also make sure there are no hairline cracks in the distributor as these will widen as the car warms and have the same effect. Check your coil wire for resistance as these are often neglected during servicing and being rubber bound, will perish and throw spark away.

I don't think a crank sensor would act in this way as they usually work or dont. But clean it anyway. Needless to say make sure the system is clean and filtered correctly.

hope you win!

let me know how you get on.

Regards

Rob