It's just not running quite right...

[e34.535i.sport]

Hey guys, having some thoughts about the car lately as it just isn't running as it should be. It's nothing terrible, it just isn't pulling like it should be. The reason I know is because when I disconnect the negative on the battery and reconnect it the car runs beautifully... For a while!

Now I know the computer has a lot to do with this but I have a theory that the fact that the car CAN run well after disconnecting the battery rules out certain things (please correct me if I'm wrong here...)

1. Valve clearences.
2. Something physically wrong slowing it down (brakes/wheel bearings whatever)
3. Fuel system issue????
4. Poor engine condition (compression test turned out V-well)
5. Engine mounts (one is leaking but seems sturdy still!)

What else could possibly cause the car to gradually go back to its normal self and not give the same power output and throttle response? The idle also worsens gradually.

Oh I'm using an EAT chip at the moment incase you don't know and for a while after disconnecting the battery it does run well with a lot of power...

Man many thanks in advance for any thoughts...

[Ferret]

Lazy O2 sensor? It could be screwing with your defined Maps...

[repenttokyo]

Hey guys, having some thoughts about the car lately as it just isn't running as it should be. It's nothing terrible, it just isn't pulling like it should be. The reason I know is because when I disconnect the negative on the battery and reconnect it the car runs beautifully... For a while!

Now I know the computer has a lot to do with this but I have a theory that the fact that the car CAN run well after disconnecting the battery rules out certain things (please correct me if I'm wrong here...)

1. Valve clearences.
2. Something physically wrong slowing it down (brakes/wheel bearings whatever)
3. Fuel system issue????
4. Poor engine condition (compression test turned out V-well)
5. Engine mounts (one is leaking but seems sturdy still!)

What else could possibly cause the car to gradually go back to its normal self and not give the same power output and throttle response? The idle also worsens gradually.

Oh I'm using an EAT chip at the moment incase you don't know and for a while after disconnecting the battery it does run well with a lot of power...

Man many thanks in advance for any thoughts...

when you disconnect the battery, the computer goes into a mode where it disregards sensor data and runs on pre-defined parameters for the first little while during operation. during this period, it gradually gathers sensor data and when it has enough, it begins to alter the operation of the engine to reflect circumstances.

This is why your car operates 'normally' after you disconnect the battery, and then goes back to the poor condition afterwards. It is a common operating procedure for almost every car.

[Morgenster]

So this means you have engine management issues, most likely coming from one of the sensors: O2, throttle position, engine and coolant temp sensors, or airflow sensor.
Time to break out the multimeter and do some measurin' of voltages and resistances.

[Paul in NZ]

your theory is fine exept "fuel system issue",because I think thats what you have got.The other thing that these cars DO respond to is a good hard run.When i visit my nephew on the other side a a mountain range(read high revs and high throttle openings on multiple occasions) ,the car runs beautifully for a couple of weeks afterwards.Have you checked with MArk to ensure you have the correct EAT chip?My car for example is a non catalytic version originally intended for leaded fuel so has different maps and no O2 sensor.The UK still had leaded petrol in 1990??

[AngryPopTart]

Do we have a thread for checking all the sensors? I need to check mine.

[whiskychaser]

Any fault codes? You have as much chance as I have of doing the stomp test - nil. If you want to give it a go with an interface/laptop just PM me. Dont you have a chess tournament coming up?

[e34.535i.sport]

Hey guys - that's perfect thanks!

Ferret/Repenttokyo/Morgenster: Much appreciated on the diagnosis!

Paul in NZ: I'm pretty sure its the correct chip but I might send him a PM just incase, thanks for the heads up!

Whisky: The chess tournament was a while back but I'm going to PM you now thanks you so much...

[Ferret]

The UK still had leaded petrol in 1990??

The UK still had leaded fuel right into the late 90's... catalytic convertors (read: unleaded fuel) were only enforced after 1992 in this country!

[e34.535i.sport]

I didn't drive it yesterday and I got in this morning and it's running like a dog. It's worse than it's ever been - normally the idle is a little rough and it doesn't seem to have full performance but now it's bucking when accelerating from low revs and feels like the petrol injection isn't quite right when taking off from the lights etc with jerkyness... Could a faulty sensor be doing this because it's been great since I disconnected the battery and it's been gradually getting worse?

I'm a bit worried as it's never been this bad!

Luckily I'm going to see the Whisky this weekend so I'm hoping he can help me find the problem!

This car is P-ing me off at the moment - it's not enough that I've got a mysterious clunk up front and the rear bumper is falling off, now it doesn't even want to drive properly!

[Morgenster]

I didn't drive it yesterday and I got in this morning and it's running like a dog. It's worse than it's ever been - normally the idle is a little rough and it doesn't seem to have full performance but now it's bucking when accelerating from low revs and feels like the petrol injection isn't quite right when taking off from the lights etc with jerkyness... Could a faulty sensor be doing this because it's been great since I disconnected the battery and it's been gradually getting worse?

I'm a bit worried as it's never been this bad!

Luckily I'm going to see the Whisky this weekend so I'm hoping he can help me find the problem!

This car is P-ing me off at the moment - it's not enough that I've got a mysterious clunk up front and the rear bumper is falling off, now it doesn't even want to drive properly!

Like I said. If the car runs fine when you just disconnected and reconnected the battery your injectors, pump, plugs, etc are fine. Your motronics sensors, however, have seen better days. If you can swap out known good ones, try that, otherwise use a multimeter to test all sensors with the values specified in Bentley.