Wierd Mis-fire

[Washburn]

Hoping for a little help...

1995 525iT 160,000 miles - always runs like a top.

I have a wierd mis-fire. Only on throttle tip in. I can hold it at any RPM unloaded, and it runs as smooth as can be. Cruising is OK too. On acceleration though, it's like it's missing on some cylinders. Lot's of vibration and lack of power.

What I've done: I had a similar problem last summer, and the following fixed it. I just did this, and it's no help.

Removed coil packs and there was oil accumilated in three of the spark plug recesses. (Causing the spark to jump I think) I replaced the plugs, and cleaned and dried everything out. That worked last time but not now. (didn't put new plugs in ...just cleaned everything this time.)

Any thoughts o great BMW wizards?

Thanks!!

[Bill R.]

A. a bad plug itself, cracked porcelain etc etc.
B. One of those Coil boots/insulators has a pinhole in the side and is arcing
out under light load

C. you've still got oil in one of the plug holes

I'd pull all the plugs and carefully inspect them to see where the arcing is occurring.. look at the end where the coil attaches for discoloring indicating a poor connection to the plug. Examine the plug/coil boots for any pinholes in the side, this area will be slightly discolored and will feel harder than the surrounding rubber.

Hoping for a little help...

1995 525iT 160,000 miles - always runs like a top.

I have a wierd mis-fire. Only on throttle tip in. I can hold it at any RPM unloaded, and it runs as smooth as can be. Cruising is OK too. On acceleration though, it's like it's missing on some cylinders. Lot's of vibration and lack of power.

What I've done: I had a similar problem last summer, and the following fixed it. I just did this, and it's no help.

Removed coil packs and there was oil accumilated in three of the spark plug recesses. (Causing the spark to jump I think) I replaced the plugs, and cleaned and dried everything out. That worked last time but not now. (didn't put new plugs in ...just cleaned everything this time.)

Any thoughts o great BMW wizards?

Thanks!!

[Washburn]

Thanks, so I might have the right idea, but need to look a little closer. Woudln't I get an engine code for a misfire like that? I've tried the 'stomp' test, but it has never worked for me...is there a different procedure for a later model perhaps?

[Washburn]

OK...I pulled a 1215 code - air volume sensor. Does that sound right? would that cause a vibration. mis-fire kind of thing? Searching my manual now...thought i would put it out there. Thanks!

[Morgenster]

OK...I pulled a 1215 code - air volume sensor. Does that sound right? would that cause a vibration. mis-fire kind of thing? Searching my manual now...thought i would put it out there. Thanks!

Those codes are hardly useful. if the MAF was at fault you'd have more problems than that.
It does indicate a problem with air/fuel mixtures or ignition. and that's no help either.
I'd start with finding out if there's a mechanical problem first: do a compression test and/or leakdown test. Also, you may want to remedy the cause of oil pooling in the sparkplug recesses. Changing the valve cover seal will avoid having to change the expensive coilpacks later.

Worst case scenario: piston rings are shot and overpressurize block + head spraying oil throug any seal that will let some through. Check the crankcase ventilation hose at the front of the head of the engine for gunk.