*SOLVED* M50 Swap w/ High RPM WOT Misfire - 24V gurus needed

[jayuuey]

Just noticed everything was disassembled prior to the swap. Did you double check timing?

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[wfkiv]

Okay-- solved the major miss-fire that was happening at all rpms. I noticed the coil pack brackets and grounds were misplaced during the process of the swap. Pulled out my trusty Harbor Freight multimeter (hey, it works for a simple continuity test!!) to test for ground...



...and grounded with a simple alligator clip to the lift point on coil 1...




Look at that, ground! Guess the coils do not ground through the mounting studs. I made temporary ground straps to link the coils in series and then ground them to the chassis. Test drive, runs pretty nicely but the high RPM WOT miss is still present. It also will miss for a second if you bog it, but that miss clears with any throttle input.

Long story short, net zero. I have not checked timing since I dropped the motor in the car... I'll pull the VC and give it a look. I still think a bad coil is more likely, they are mismatched Bremi and Bosch as you can see in the photos. Stay tuned!

[AndrewBird]

Can you get a video showing the miss? Would be helpful for diagnosis.

[wfkiv]

Can you get a video showing the miss? Would be helpful for diagnosis.

Sure, great idea! I'll get a friend to ride in it with me tomorrow morning to help with the video. The car is pretty damn loud so I think the miss will be easily detectable over video. I'll post it tomorrow afternoon.

[wfkiv]

Video of the miss. Recommended you wear headphones, miss is slight and tricky to detect.

Excuse the 4 cylinder coding plug. Multiply indicated rpms by 2/3 {6K = 4000 rpms | 7K = 4700 rpms}

5th gear pull. Miss comes on around indicated 6400 RPMs (actually 4300 rpms). In lower gears it will pull strong through the miss to redline.

https://youtu.be/aALJUylPCiA

[wfkiv]

SOLVED!

I picked up one coil and replaced it with coil #1. No change, moved down to coil #2 etc. Turns out coil #3 was bad. Now the car runs perfect, all misfires are gone including the original high RPM WOT miss. Now I can fully enjoy my non-VANOS 24V! :)

[jayuuey]

Thats great! Especially since your vid doesnt reveal much. Glad to hear its working great now.

My coils are original on my S50 since the date stamp says 11/94 or something. I wonder how much performance can be restored by putting in a fresh set.

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