Results 1 to 9 of 9

Thread: V12 Misfired cylinder 6 could not pass smog check

  1. #1
    Join Date
    Apr 2005
    Location
    los angeles
    Posts
    6
    My Cars
    BMW 750IL

    Question *UPDATE* V12 Misfired cylinder 6 could not pass smog check

    Hi, My 1996 750 iL could not passed the smog check because the "check engine" light was on. After undergoing some testing, the cause was a misfired on cylinder 6.
    Mechanic recommend changing the spark plugs and the ignintion coil. Has anybody done this themselves without shelling big bucks for the labor.
    Do I need to change all 12 plugs? What's the best spark plugs for this car? Thank you in advance.
    Last edited by amazonarcher; 04-29-2005 at 05:25 PM.

  2. #2
    Join Date
    Mar 2005
    Location
    So Cal
    Posts
    70
    My Cars
    none
    Try swapping a coil from another cylinder to your misfiring #6. Then see if the misfire follows the coil or stays on #6. If it stays on #6, swap the fuel injector and spark plug with another cylinder (one at a time). This method should be able to tell you if you have a spark or fuel problem. Finally, you could check compression on #6.

  3. #3
    Join Date
    Sep 2003
    Location
    Stanley, NC
    Posts
    1,060
    My Cars
    '06 Lexus IS350
    Will be very difficult for you to swap a coil from one cylinder to #6 because the 750 doesn't use coil-on-plug. We do have two coils though, if you look on the left and right side of the engine behind the air boxes you will see a unit that has a rounded cover at the top of it with a lightning bolt on it - you can swap that. At the front of the engine on the left and right side are the distributor caps and rotors, these are interchangeable.

    Yes you can change the plugs yourself but plan on it taking all day - I did it and it was a royal pain in the ass. You can change just one plug but the others are probably in as crappy shape as #6 if that is really the trouble. Buy OEM.

    Did you go to get tested with the check engine light on? That is an immediate fail, no matter what the cause is.

    Did you have the light reset? Did the trouble come right back or could it have just been a fluke that occurred?

  4. #4
    Join Date
    Apr 2005
    Location
    los angeles
    Posts
    6
    My Cars
    BMW 750IL
    Yes, I got the smog check done when the "check engine" light is on. The car passed every other tests expect fuctionality. The diagnostic said misfired on cylinder 6. I didn't get it reset and re-tested again. The mechanic recommend changing the ignition coil and the plug before re-testing.
    The funny thing is the "check engine" light came on the same day my registration expired. I don't know if it was programmed by the dealer or not. I mean the car is still running smoothly and I don't have any problem starting it.
    I will bring the car in to the dealer and get a proper dignostic. I will update the forum when the problem is fixed. Thank you for the replies guys.

  5. #5
    Join Date
    Apr 2005
    Location
    los angeles
    Posts
    6
    My Cars
    BMW 750IL

    *UPDATE* V12 Misfired cylinder 6 could not pass smog check

    Going with the mechanic recommendation, I changed all the spark plugs and the ignition coil. Problem solved. Like they said, the car is purring.
    BMW service wanted $20/spark plug ($240) and $92 for ignition coil plus labor cost to fix the problem.
    I decided to take it to an independant auto shop. I purchased the spark plugs myself, Bosch Platinum 4+ (NGK was out of stock at the time of purchase) for $5.95 each. Purchased the ignition coil from Pacific BMW for $92. It took the mechanic about 2 hrs to replace everything. Labor cost $140. Overall, I think I save about $200-$300 (money will be used to update to crystal tail lights).
    A few board members recommended replacing the old spark plugs with OEM spark plugs (NGK), to my suprise the old spark plug ins my car were made by BOSCH and have the BMW logo stamped on them. Did BMW decided to change the stock spark plugs from BOSCH to NGK recently?
    I will update if there are problems arises from the new BOSCH plugs.

  6. #6
    Join Date
    Mar 2003
    Location
    Seattle, WA
    Posts
    1,239
    My Cars
    '98 750iL, '88 750iL, '71 Charger, '67 Belvedere
    Only 2 Hours of labor to replace spark plugs and coils sound amazing to me. The spark plugs are a bear to get at.

    I had a problem with misfires. It was caused by corroded terminals on one of my distributor coils and the distributor cap. This is somethign that is easy check visually with no tools. Just unplug the cables and look.
    Dave Clement
    Chief Technology Officer, Seattle 7's
    1998 750iL w/2001 Facelift
    http://www.cardomain.com/id/daveclement
    http://www.seattle7s.com


  7. #7
    Join Date
    Apr 2005
    Location
    los angeles
    Posts
    6
    My Cars
    BMW 750IL
    Quote Originally Posted by DaveClement
    Only 2 Hours of labor to replace spark plugs and coils sound amazing to me. The spark plugs are a bear to get at.
    My car was fixed by an asian mechanic with small hands and he was able to manuever around the engine block without any problem. I saw the whole process, the 12 spark plugs took sometimes to replace but the ignition coil was easy, probably 15 minutes.
    A few of my front and rear bumper sensor was coming loose and I have him fixed them too. It was amazing to see him pushed them back into position without any tools, just by putting his whole arm in the smallest available openings under the car.
    I have driven the car more than 20 miles , smooth as ever.

  8. #8
    Join Date
    Apr 2005
    Location
    los angeles
    Posts
    6
    My Cars
    BMW 750IL
    Quote Originally Posted by DaveClement

    I had a problem with misfires. It was caused by corroded terminals on one of my distributor coils and the distributor cap. This is somethign that is easy check visually with no tools. Just unplug the cables and look.
    The mechanic also told me there is some corrosion on the #6 distributor coil terminal when he was replacing the spark plugs. This might be one of the cause of the misfiring. He advise me to replace it soon.

  9. #9
    Join Date
    Mar 2003
    Location
    Seattle, WA
    Posts
    1,239
    My Cars
    '98 750iL, '88 750iL, '71 Charger, '67 Belvedere
    I never considered it before, but I can see how small hands would help tremendously. Unfortunately, I did not come equipped with that feature.
    Dave Clement
    Chief Technology Officer, Seattle 7's
    1998 750iL w/2001 Facelift
    http://www.cardomain.com/id/daveclement
    http://www.seattle7s.com


Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •