Just bought old E34 - got a few issues though!

[DRB]

Hi guys, I've just bought a '93 E34 520i for £700. I know old cars are going to be a bit of a risk but it appeared in good condition, low mileage (77k), and seemed to run perfectly on a test drive.

Unfortunately it seems to have a problem when the engine is warm. After about half an hour of running it starts to misfire, looses power and stalls. This seems to happen first at higher revs, but after a minute it wont idle or run well at all.

When cold it starts and runs perfectly at all revs, and sounds spot on for a 17 year old car.

I have limited mechanical knowledge but have checked a few things, oil and water look ok, coil packs and spark plugs look fine but I dont really know how to test the coils properly.

I assume it might be something to do with the coils, crank posistion/o2/maf sensors, or something to do with the fuel system. Anyone have any suggestions of where to start?

I was thinking of buying a set of used coil packs of ebay for £30 and seeing if that worked?

There are no warning or check engine lights showing, someone told me there is no point getting a garage to read a fault code unless this happens, I don't know if this is correct?

Thanks for your help!

[steve6304]

it would be worth having the fault memory checked, there could be intermittent faults lurking in the memory, get them all cleared thendrive again and have it re-checked after the fault has re-ocurred, then you know you have the actual fault, not a red herring.
somr time ago though I had similar problem with same engine, turned out to be a faulty engine temperature sensor, it went short circuit to ground which basically cuts off most of the fuel to the injectors.

[Touring442]

It doesn't have an engine check light, but you can still read some fault codes. It could be almost anything - crank sensor for example. Unless all the coil packs are faulty, that won't be it. It won't be a MAF (the car will run without one - the next time it farts about, just unscrew the connector), but it could be a fuel pump. E34 pumps tend to die after 10-15 years and they overheat and sieze. They can give your symptoms, or just have sudden death.

Most likely - fuel pump, crank sensor.