E34 misfire when warm

[DRB]

Hi guys, I'm having trouble with my e34 520i, the engine runs perfectly when cold but after about 20mins it start to misfire. First this happens at higher revs, then it starts to struggle at all revs and soon stalls. If you leave it to cool down it starts fine, then the process starts again.

The oil and water look ok, spark plugs look fine, and I replaced the coil packs with another set of used ones but the problem persists.

I was wondering if one of the sensors (crank/o2/MAF) is to blame or something to do with the fuel system? There are no engine fault lights showing.

I'll probably take it into a specialist next week but with the intermittent nature of the problem and no fault codes i was wondering if it will be hard to diagnose or if anyone has any other ideas! Thanks in advance...

[Pumaracing]

Sounds very like a fuel filter full of gunge which gets stirred up until it blocks the element solid as the car drives and then settles out again after a rest.

[anonymous-user]

Connections to the air flow meter? clean it up, or cut the plug of and put indevidual speae conectors on each wire.

[DRB]

Cheers for the replys, I've been trying to diagnose this further and it definately seems related to the engine temp, and the temp of the engine compartment. The fault will appear when the car is just left to idle, not just when driving around, am I right in thinking the fuel filter is somewhere near the tank and therefore shouldn't be affected by temp?

For example once the car starts to misfire if you switch off and open the engine compartment the problem will go away for a few minutes, if you leave the bonnet shut it will come back straight away.

Also I have tried disconecting the air sensor, I belive the car reverts to a more 'simple' ecu setting if you do this but should still run, the problem is exactly the same though.

I'm no mechanic though - this is all from info off the net please tell me if i'm talking rubbish!

[Pumaracing]

At the moment you don't know whether it's fuel or spark failing so I suggest you get the car to a rolling road diagnostic centre that can test it under load and see what fails as it gets hot. Steer well clear of main dealers and back street garages who will just replace things at random and at your expense.

[mad4amanda]

get the fault codes read it will pinpoint the issue .
Or try the 5 series forum, where are you based?

[OctyVrs]

Are there separate temperature senders for dash and ecu on this model? I know you said you're taking it in somewhere but i figure temp check only takes a couple of mins to measure resistance when cold and resistance across temp sender when struggling.

Just for completeness a continuity test will identify the pins on the ecu harness to see from the ecu's point.