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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Thu, Jul-05-2018, 03:37:23 AM   #1
adept
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Default Bosch Pt +4 spark plugs: prongs broke off and caused misfire

Found a serious issue with the Bosch platinum +4 spark plugs (FGR8KQE) I installed 5k miles ago. I'm now switching to NGK and starting with the standard copper plug model 2288 (BKR6EK). I've been using those on my S2000 without issue. Plus, some research indicates other E36 & E46 users having good experiences using NGK plugs.

Problem statement: Engine would sometimes start misfiring after stopping back to idle.

Symptoms:
  • Intermittent misfiring occurrences when coming back to idle, only about once per drive.
  • Engine was strong and powerful when the misfire wasn't occurring.
  • CEL code P0306: "Cylinder 6 misfire detected."
Findings: All 4 of 4 prongs on the cylinder 6 spark plug were broken off. 2 of 4 prongs broken off on cylinder 5. The rest of the spark plugs looked poor after only 5k miles.


Question for forum members: Should I worry about any damage, or perform further tests/maintenance? The engine is actually running fine now. I can't tell if there are any issues. I'm guessing the prong could have been pulled out of the exhaust valve on the vacuum part of the cycle. However, I'm also thinking that the prongs could have only broken fully off after I just removed the plug.


Full story:

Took the e36 to the track for three consecutive weekends, then it sat for ~4-5 weeks.

My wife and I decided to take it out to dinner to keep the tires fresh, and the car randomly started misfiring at idle. I killed the engine quickly, and then it started back up perfectly. It ran the rest of the night just fine. So I chalked it up to a freak occurrence.

But then I drove it to work and had more of the same. Car would start misfiring after coming to idle, I'd pull over, start it back up, and it would run smoothly. This happened twice, and this time it threw a CEL (check engine light). The code was P0306: "Cylinder 6 misfire detected."

The strange thing is, I even drove the car to redline a couple times after this, and the engine pulled powerfully.

So anyways, I started my diagnosis by testing the coil packs. Each one measured the correct 0.4-0.8 ohms (between left and right pins 1 & 15).

But then I pulled the plugs and the issue was obvious. The plug on cylinder 6 was in terrible shape, and didn't retain any of the prongs.

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Old Thu, Jul-05-2018, 05:36:17 AM   #2
westopher
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Default Re: Bosch Pt +4 spark plugs: prongs broke off and caused misfire

Had the same thing happen on cyl 5/6 on my car. Switched the plugs to NGK and had no issues for the next 8k. Then blew my HG. Car had no bottom end, piston, valve damage etc when the motor was pulled apart. The Plug ends seem as though they just disintegrated or left the combustion chamber. I wonder however if the HG issue was related in any way.
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Old Fri, Jul-20-2018, 02:50:57 AM   #3
adept
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Default Re: Bosch Pt +4 spark plugs: prongs broke off and caused misfire

My best guess is that the plug ends were disintegrated. I looked in the cylinder with a bore scope and didn't find anything. I also did a compression check, and found all 6 cylinders were in good health (200-205 psi).

Replaced the plugs with 2-prong NGK BKR6EK (2288) and although it ran, the idle was a little poor.

I then replaced the plugs with 4-prong, "laser platinum," NGK BKR6EQUP (3199) and the car has never idled better.

Hoping that nothing else pops up from this down the road.
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Discussing Bosch Pt +4 spark plugs: prongs broke off and caused misfire in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)