Bimmerfest BMW banner

1 - 8 of 8 Posts

·
Registered
Joined
·
30 Posts
Discussion Starter #1 (Edited)
My 2003 325ci with 99k miles recently threw a misfire code cylinder 5 while I was on a road trip. Was night time so I had to plod home the remaining 150 miles running rough.

Took me a few days to get to it.
1) Pulled the code (misfire and fuel cutoff) and followed the process I have used many times on my E39 - swap the coil and see if code moves. No change.
2) I put a new coil on cylinder 5 with no improvement or change
3) Pulled spark plug - old plug VERY oily
4) Installed new plug - no change

So cylinder 5 not firing with a new plug and new coil. :( What should I look at next? I have NOT tried any electrical measurements. BTW all electrical connections look clean and in good shape - no melting or charring.

Any and all recommendations welcome. Thanks in advance.
 

·
Registered
Joined
·
5,349 Posts
Try to see if the plug actually fires by removing the coil pack and inserting a spark plug into it. Then place the coil pack with the plug on top of the engine where you can ground the spark plug’s threads. Then crank it. The engine computer (DME in BMWspeak) provides a ground to the coil when it wants the coil to fire. The coil has 12VDC as long as the ignition is in the run or start position. You should check to make sure that the coil is getting power.

The DME uses an electronic component known as a metal oxide field effect transistor (MOSFET) to fire each coil. So, if the coil firing test shows that the spark plug isn’t firing and the known good coil is getting 12VDC, the next step is to see if that cylinder’s MOSFET is bad.

If the coil/spark plug are firing when it’s placed on top of the engine then you need to have that cylinder’s compression checked. In fact, check the compression on all cylinders. If the compression of the offending cylinder is greater than 10% less than the cylinder with the next lowest compression reading you have a mechanical problem.
 

·
Registered
Joined
·
443 Posts
Haha I was in agreement with marco on this.

The shadow kinda throws it off.

Where did he chunk go is the next question


Sent from my iPhone using Bimmerfest
 

·
Registered
Joined
·
30 Posts
Discussion Starter #8
The chunk bounced around in the cylinder for approximately 200 miles. Scoped it and cylinder walls badly scored. Found a strong donor engine with similar miles and had them swapped. Original engine was full of sludge and deposits - donor engine clean and bright. Certainly wasn***8217;t in the plan to invest in this much work but I now have a vehicle that I should get another couple 100k miles out of.
 
1 - 8 of 8 Posts
Top