E38 740i Power Issue - BMW Forum

Lexx_DMC · 07-26-2005, 09:02 AM

Hi all,

Hope someone can help. I've been having an issue with my E38 when taking it on motorway journeys. When I hold a steady 80mph or more, it seems to upset something in the car. It starts rumbling, till I slow down. Then, from that point on, it idles roughly. When at a standstill, the car bounces as if it's mis-firing. While it's in this state, there is a lack of power, both from a standstill, and at high speed. This problem is immediately rectified if I stop the engine, then start it up again.

It just seems to have problems at high RPM's, eg 2500 +. She also gets upset if I pull away quickly, getting into the 4000RPM area

Can anyone advise what might be wrong? I am not sure.

Thanks in advance

nathan56989 · 08-15-2005, 11:11 PM

How long has it been since your last spark plug change. you may wanna check them. sounds like it may be a mass air flow meter going bad also. i'm not saying go out a buy a meter but i ahve had one or two e38's do that due to a mass air flow meter. could possibly be the coils going bad also. thats jsut a few things.
it could also be a cam sensor. is there a check engine light on.

Lexx_DMC · 08-16-2005, 03:47 AM

Thanks for the reply. The spark plugs have just been changed, and it did it before that as well, so i've ruled them out. The "Check Engine" light has never come on. The car is happy as long as I don't push it.

A few people have suggested it could be one or more of the coils. I am having them looked at (and probably replaced) on Monday.

I'll see what happens there. Others have suggested it may be a bad CAT or CATS. I'm hoping not as they're a bit expensive, but I'll see on Monday I guess. I'll post a reply once the garage has had a look at it.

Joe Flynn · 08-29-2005, 03:03 PM

Quote:

Originally posted by Lexx_DMC@Jul 26 2005, 07:02 AM
Hi all,

Hope someone can help. I've been having an issue with my E38 when taking it on motorway journeys. When I hold a steady 80mph or more, it seems to upset something in the car. It starts rumbling, till I slow down. Then, from that point on, it idles roughly. When at a standstill, the car bounces as if it's mis-firing. While it's in this state, there is a lack of power, both from a standstill, and at high speed. This problem is immediately rectified if I stop the engine, then start it up again.

It just seems to have problems at high RPM's, eg 2500 +. She also gets upset if I pull away quickly, getting into the 4000RPM area

Can anyone advise what might be wrong? I am not sure.

Thanks in advance

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I have a similar problem with my 740il but the check engine light comes on and it gives a multi missfire code I have changed the plugs wires and coils and it is still there, it is in the shop for diaognistic check now

Dirty_Tool · 08-31-2005, 01:55 AM

Joe, sounds like you may have either bad cats or possibly intake leaks causing the misfires since you have already eliminated the plugs and the coils. Good luck to you.

Lexx,
By your description this sounds like classic misfiring with cylinder cutout seeing as the problem resets itself with a cycle of the key then comes back under hard acceleration. The only issue is that your check engine lamp SHOULD be coming on and its not which makes it complicated. Hopefully your mechanic can get to the bottom of it quickly. Best of luck to you too.

DT

car34 · 09-11-2005, 10:29 PM

Hello, My problem was a bit different but you may have the some thing going on.

On my 95 740. What it turned out to be was. the plate on the back of the intake manifold. If you look at it their is a diaprham on the right side of the plate which I think is part of the PCV system.Mine would run ok them it would act like it lost two cylinders. Run bad at idle then would run just fine.Anyway I replace the plate and all my problems went away. Plate was only like $40.00 much cheaper them coils!