525i help needed please !

E34 525i 2.5 24v DOHC.

The car starts and runs perfect most of the time.
Every now and then after it has started in the morning it will run fine and then suddenly become sluggish.
Pressing and holding the throttle flat it revs to +-3000 and then drops back down, then up again and back down, it will not rev up.
Also driving it like that is impossible, pulling off is nearly impossible.
When I unplug the Air sensor it runs better but heavy on fuel, sometimes that doesn't even help.
Anything to try or test ???

Does the engine shut off at all after revving to 3K?
And how does it idle in that state? should be around 750 to 900 rpm I think.

I would try and test or have a look at your fuel pump. I'm having similer problems with my 90 525i and I'm replacing the fuel pump. Which will fix my problem. Another thing, when was your fuel filter last changed?

Once the car is warmed up, will it run fine or not?

Agreed with Rob, change the fuel filters first, if still having problems hook up a fuel pressure guage to see where your at and go from there.

Somedays it will be fine and not do it at all like today. Car ran beautifully today. Other days it just goes haywire.
Will see if I can change the fuel filters this weekend.
We thought it was temp related, when the car gets hot. But like today it was hot and nothing went wrong.
Idling is a bit eratic when it does that.
Switch it off and on a few times and it goes again.
Other days you must sit and wait for it to come right, up to 2 hours sometimes.
Might it be knock sensors or something ?

I had a similar problem on my 325i (same engine) and a new coil pack fixed everything. Do you have hesitation or bogging as well?
If so you might want to check the coil packs/boots and plugs.
Also might want to try cleaning the ICV.
Also if the check engine light is on you should read the codes.

Quote:

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Originally Posted by gt90

I had a similar problem on my 325i (same engine) and a new coil pack fixed everything. Do you have hesitation or bogging as well?
If so you might want to check the coil packs/boots and plugs.
Also might want to try cleaning the ICV.
Also if the check engine light is on you should read the codes.

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Not to hijack the thread. I have a hesitation when pressing on a gas pedal. The car does not react, you wait for maybe a second and it picks up. Or I release the gas, press it a little slower.
You had the same hesitation and new coil packs fixed it?

I agree that it sounds like a fuel starvation problem. I've had similar with cars other than my E34. The junk inside the filters moves around. Some days it wont bother you other days it will clog up. Starting the car a few times and jolting the fuel from rest through the pump will stir the junk up.

When I unplug the Air sensor it runs better sometimes but then it smokes and is heavy on fuel.
Going to change the fuel filters and check the spark plugs and wires.

Is it safe to unplug the MAF while the engine is running?

It would appear that your O2 sensor is working then (I assume that it is black smoke). Is there a 'miss' anywhere?

Yes, black smoke and you can smell the fuel at the back.
No, miss when I do that but I get like 200km on a tank then.
When it is real bad then the sensor makes no difference when in or out.
Somebody today said it sounds like the computer box is busy going....
What's the 2 sensors on the front of the head, one is silvery and looks like it goes into the head next to the cam and the other is long and black and runs accross the front of the head bolted to the outside.
My thinking is maybe a faulty knock sensor that is retarding the timing too much.
Can I undo it and leave it hanging in a piece of spunge or something to test ?

Ok, installed a new fuel filter today.
Also found a leaky fuel pipe on the fuel rail, replaced it with a new piece of pipe.
Let's see how she goes now.
Another thing, every once in a blue moon the battery would go dead, any idea what could cause a power drain ?

Quote:

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Originally Posted by debeerd

Ok, installed a new fuel filter today.
Also found a leaky fuel pipe on the fuel rail, replaced it with a new piece of pipe.
Let's see how she goes now.
Another thing, every once in a blue moon the battery would go dead, any idea what could cause a power drain ?

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I am interested to see if this fixes the problem. Just for my own knowledge.

Nope, car just started doing it again.
Going to see if I can check the fuel pressure, any idea what reading I should get ?

check the battery voltage when shut off and when running.

Quote:

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Originally Posted by debeerd

Ok, installed a new fuel filter today.
Also found a leaky fuel pipe on the fuel rail, replaced it with a new piece of pipe.
Let's see how she goes now.
Another thing, every once in a blue moon the battery would go dead, any idea what could cause a power drain ?

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check your grounds, especially the one that goes from the chasis to the engine, its located on the motor mount

I thought the M50 didn't have knock sensors, which is why we have to use 91+ octane.
Am I wrong?
-ashley

Battery was 12.47V before I started. After starting it runs 13V-14V. When the motor is not messing around it runs 14V+.
I'm starting to think that is is fuel pressure, where is the high pressure pump mounted ?

The fuel pump is in the tank it self. To get to it you need to take the carped out of the tunk and remove the black plate to the right of trunk. Fuel pump is in there.
I've just replaced mine. Car working perfect again. :)