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Thread: 89 635csi Manual not firing on cylinder 6

  1. #1
    Join Date
    Aug 2012
    Location
    Metro Detroit
    Posts
    229
    My Cars
    88 635csi, 12 328xi

    89 635csi Manual not firing on cylinder 6

    I have 125-PsI +- 5 across the board little low but over 250k miles on the engine.

    I have a rough running issue. cylinder number 6 does not appear to be working.

    I pull the wire to cylinder 6 and the engine continues to run exactly the same. Pull the wire to cylinder 5 and the car starts to stumble worse.

    Cylinder 6 Has Spark and it's Strong. New Plugs. but the Cylinder 6 Spark Plug came out black but not wet.


    I have Spark, Compression, and Air my only thought is fuel at this point.

    I swapped Injector 5 with Injector 6 and have not noticed any difference in running. the problem hasn't moved.

    I have motronic DME 013 Yellow Label 1.3 but i'm not sure of a good way to test if injector 6 is firing as pulling the rail doesn't give me much of any room to actually see whats going on with the huge plastic wiring loom in the way of the injectors. Looking for some help on this one.


  2. #2
    Join Date
    Oct 2015
    Location
    Illinois
    Posts
    120
    My Cars
    740 735 635 535 318is
    First, I would remove the valve cover and have a look at the cam lobes. Make sure oil spray bar is good with out loose sealing bolts. Check/ set valve lash. Putting an extra (+) .002 to .004 on the lash helps smooth out the idle. So set the lash around 0.014" cold.

    Can pass a compression test with a wiped cam lobe. Would be good data to get leak down rates along with compression.

    Second, I would point an infrared laser thermometer at the exhaust ports when running. This will indicate if you have a noncontributing cold cylinder. Helps to do this right after running some load.

    M30's are finicky on spark plugs. Make sure you have the regular Bosch silver plugs and .032" gap. These engines run best on the oem recommend plugs and not platinum or other types of plugs.

    Sent from my SM-G900V using Tapatalk

  3. #3
    Join Date
    Aug 2012
    Location
    Metro Detroit
    Posts
    229
    My Cars
    88 635csi, 12 328xi
    Quote Originally Posted by Dschart View Post
    First, I would remove the valve cover and have a look at the cam lobes. Make sure oil spray bar is good with out loose sealing bolts. Check/ set valve lash. Putting an extra (+) .002 to .004 on the lash helps smooth out the idle. So set the lash around 0.014" cold.

    Can pass a compression test with a wiped cam lobe. Would be good data to get leak down rates along with compression.

    Second, I would point an infrared laser thermometer at the exhaust ports when running. This will indicate if you have a noncontributing cold cylinder. Helps to do this right after running some load.

    M30's are finicky on spark plugs. Make sure you have the regular Bosch silver plugs and .032" gap. These engines run best on the oem recommend plugs and not platinum or other types of plugs.

    Sent from my SM-G900V using Tapatalk

    Appreciate the info. Spark plugs are currently gapped at .032 and are BOSH Copper Core plugs that I just replaced while attempting to fix this issue. I've not pulled the valve cover recently. would be surprising to see the lobe wiped out but i haven't done a valve adjustment in some time i swaped the head on it 3 years ago and i've only put about 500 miles on it. I'll report back with temp when running to verify that the cylinder is indeed not running. Dont' have the proper tools to do a leak down test at this time.


  4. #4
    Join Date
    Sep 2016
    Location
    North Florida
    Posts
    111
    My Cars
    1983 633csi, 2017 540i
    I'd try listening to that injector with a mechanic's stethoscope to see if it's firing.

  5. #5
    Join Date
    Feb 2009
    Location
    Pittsburgh, PA
    Posts
    1,718
    My Cars
    '86 635CSi, '08 128i
    You've done everything I'd have done and then some. My only suggestion is to check the wiring harness plug internally for a bent or damaged connector pin. B35 injector plugs are retained by the conduit cover and can be internally damaged...#6 is usually the worst off. I'd assume the plug is properly seated on the injector but it might be pushing a pin into the connector internally.

    ..remember those old 'noid' injector testing lights? Might be handy if you had one.
    Save the manuals!
    '08 128i 6MT, '86 635CSi 5MT (B32, Motronic 1.3, WBO2, G265, 18# FW, 3.46 torsen)
    Past projects:
    '96 318iS, sold 4/23 '90 535iM, RIP 1/23 '90 535iA RIP 6/22 '91 318i, sold 7/19 '97 M3 sedan, sold 11/18 '85 735i, RIP 2/18 '92 325iC, sold 7/16 '91 318iS, sold 6/16 '84 745i, sold 10/14 '82 633CSi, traded 9/12 '90 325i, RIP '87 325 sold '89 525i, traded '87 325iS, RIP

  6. #6
    Join Date
    Oct 2015
    Location
    Illinois
    Posts
    120
    My Cars
    740 735 635 535 318is
    https://youtu.be/RO12NiE5g1E

    Check this video, good info on detecting a misfire.

    Sent from my SM-G900V using Tapatalk

  7. #7
    Join Date
    Aug 2008
    Location
    Sydney Australa
    Posts
    2,482
    My Cars
    1x633, 1x E3 2 DR Racer
    125 psi is very low. My 633CSi had 125 across 3 cylinders and 120 across the remaining 3 prior to replacing the engine. I went to the workshop manual and it noted a bad engine was one reading under 145psi and that any engine under 145psi should be replaced. Consider a freshen up in the future.
    1977 633 CSi RHD Euro. S38B38 3.9L M5 Transplant. 5 Speed Getrag Dogleg. 3.73 LSD. 417hp, 369lb/ft
    1971 3.0CS E3 2dr Alpina Special Coupe Racer, 347hp, 295lb/ft

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