My son just bought this car and the previous owner said it would run fine until it got hot and then it wouldn't accelerate and would idle poorly. Any ideas ? I have relays, fuel pumps and the like on the short list. Bummer is this is a european car and I don't expect to be able to find lots of parts out there, any leads on those? remove nospam if you prefer to reply with email. jd
Could be fuel evaporation - the formulation of petrol when it was built didn't allow evaporation as easily as these days. So check all routing of pipes etc and for any missing shields, and that under bonnet airflow is correct.
Where are you located: US or UK?
Bill, We are in North Texas, USA. jd
A car this old could have enough miles on it to have worn out the distributor bushings. This causes the timing to become very erratic, the engine misses and stumbles, especially at high rpms, which causes it to be unable to accelerate. It happened to my '84 318i at somewhere around 300k miles. Just one more possibility for your list.
The 635 is Motronic so it won't have a separate distributor drive shaft, it's bolted to the end of the camshaft. But a new rotor arm is worth the money as it's probably ancient! I'd also check the distributor cap for wear and pitting. You'll get replacements from
Does the temperature gauge show the car to be overheating?
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Here in Omaha, there's a few 3.5L m30 motors show up a month. My '86 535i has the same motor as the 635. I have plenty of fuses, relays, and some other ignition/injection parts, including a working set of 6 injectors for that motor. If you can't find something cheap, let me know. I also have a compilation CD of a few DIY repairs that reference that body or mechanicals and the engine. Two junk yards here have a small selection of main fuel pumps (pretty sturdy). The in-tank pump my be your problem. If it doesn't work, the main pump may be overheating and beginning to fail. I replaced my in-tank pump with one for a '76 Vega and it can pump hard enough to be the main pump! $38 at Advance Auto Parts and it is also used to power the 350 Chevy motor so it should handle the 42-45 pounds the m30 needs (even though it's only a helper pump). I have found that you can run the 535/635 without the in-tank pump, but with a filtered suction tube, and be OK as long as it's driven peacefully. I did for a year. These cars have lots of cross-over parts internally so they are easy to find.
Bill in Omaha (major snow melting!) '86 535i
It has a freeze plug out (rusted) so we will need to take care of that before we start her up. From talking with Ed (po) it didn't overheat, just had problems in summer, thanks for all your help. jd
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