The e30 developed a misfire on the final leg of our Sunday tour. It’s fixed now.

Monday

  • left the car parked
  • researched the issue on the e30 forums, came up with a million different ideas (see below)
  • for good measure sent an email to my mechanic

Tuesday

  • got up early planning to check the spark plugs
  • didn’t have the right socket, went to Pepboy’s and bought a 21mm spark plug socket
  • my mechanic emailed me to confirm that I should start with the plugs
  • blew out each port with compressed air and removed plug #1
  • looked dirty, though later my mentor and mechanic told me that it didn’t look that bad
  • left the job as it was, Trina went and picked up “Bosch Super Plus WR8LC+” spark plugs for me

Wednesday

  • got up early
  • methodically loosened each plug with the breaker bar
  • removed each plug with socket driver
  • labelled each plug
  • plug #4 was pretty black, #5 was totally clogged, #6 was blistered
  • plugs were pre-gapped but checked anyways, all were .30mm
  • applied anti-seize compound to the threads on each plug and re-threaded by hand
  • tightened to finger tightness with extension and socket
  • tightened to 22 ft. lbs. with torque wrench
  • discovered tips on plugs are larger than the plugs on HT wires
  • removed plugs again and removed tip with vise grips
  • re-installed plugs
  • after stalling 2-3 times managed to keep it alive long enough for a drive around the block
  • still mis-firing, stomp code 1222 (“Lamda Control 1”, umbrella code for too much o2)
  • checked HT wires, #1 seemed just ever so slightly mis-seated at the distributor cap
  • car ran just fine after that

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Wrap Up

My mechanic says based on the buildup that the problem was plug #5 and the miniscule amount that the #1 HT wire was out by would have no effect. I’m not 100% sure with that diagnosis but the car is running and I’m happy. I will sand blast my old plugs and save them for spares as I will need to replace #5 in 3,000 miles. Or less.

His sound advice is not to put any more money into this m20 engine, which could run for a long time in it’s current state. And save for an engine swap, specifically a 3.2L e36 M3 motor a.k.a S52. If I get lucky I may get the engine for $2K, but install will be a whole other matter. If I do an engine swap then I may paint the engine bay at the same time.

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Photos of the worst two plugs, #5 (gap filled with buildup) and #6 (blistered):

Technicals Spec List

e30 M20 Spark Plugs: NGK ZGR5A or Bosch Super Plus WR8LC+
Spark Plug Socket Size: 21mm
Spark Plug Torque: 15 – 22 ft. lbs. 

Misfire Information

For reference, diagnosing a misfire includes (but is not limited to) the following systems / parts:

  • spark plugs
  • spark plug wire set
  • distributor cap & rotor
  • ingition coil
  • fuel pressure / fuel pump
  • fuel injectors
  • AFM (air flow meter) & related hoses 
  • vacuum leaks
  • timing belt
  • coolant temperature sensor
  • o2 sensor

October 31, 2012 mechanical, repairs