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Old 04-01-2011, 10:44 PM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K

- How to diagnose a BMW E39 engine misfire (1)

BMW E39 engine misfiring is ALWAYS due to one of the following:
  • gas
  • air
  • spark
  • compression
  • timing
Tribal summary on BMW E39 specific misfire culpability: (after reading hundreds of E39 misfire threads and manually collating the results)
  1. bad fuel [air:fuel ratio]
  2. clogged fuel filter [air:fuel ratio]
  3. bad fuel pump [air:fuel ratio]
  4. clogged engine air filter [air:fuel ratio]
  5. vacuum leaks in hoses or the air-intake conduits [air:fuel ratio] (1) () (3)
  6. bad ignition coil packs [spark] (1)
  7. bad ignition coil boots, aka "spark plug socket" [spark] (1)
  8. bad or ill fitting spark plug valve cover seals [spark]
  9. worn or fouled spark plugs [spark] (0) (1) (2) (3) (4) (5) (6)
  10. bad mass air flow (MAF) sensor or meter [air:fuel ratio]
  11. bad DISA valve flap [air:fuel ratio] (1) (2)
  12. bad DISA valve o-ring [air:fuel ratio] (1) (2) (3) (4)
  13. worn fuel injector seals (o-rings) (1) (2)
  14. bad fuel injectors [air:fuel ratio]
  15. bad 02 oxygen sensors [air:fuel ratio]
  16. bad camshaft position sensor CMP, aka CPS [spark? timing?]
  17. bad crankshaft position sensor CKP, aka CPS [spark? timing?]
  18. bad ground wires [spark]
  19. bad fuse or relay [gas, spark, timing]
  20. bad electrical wiring [gas, spark, timing]
  21. bad engine computer DME, aka ECU [spark]
  22. intake manifold gasket leak [compression, air:fuel ratio]
  23. bad crankcase oil separator valve CCV, aka PCV [air:fuel ratio]
  24. bad idle control valve ICV [air:fuel ratio] (1) (2)
  25. bad throttle position sensor TPS [air:fuel ratio]
  26. bad throttle body [air:fuel ratio] (1)
  27. bad throttle body o-ring seal [air:fuel ratio] (1)
  28. bad VANOS seals [compression, air:fuel ratio]
  29. collapsed lifters due to lifter-bore scouring [air:fuel ratio] (1)
  30. valve cover gasket (VCG) leak [air:fuel ratio]
  31. head gasket leak [compression, air:fuel ratio] (1) (2) (3)
  32. overheating complications, e.g., cracked heads, warped blocks, cam seizures, contaminated main bearings, coolant-caused hydrolock, & cracked rings, piston, & valve damage (1)
BMW E39 tribal knowledge misfire-troubleshooting algorithm:
  • If your engine is misfiring, immediately turn off the ignition
  • Wait 30 seconds before restarting the engine (this reputedly resets emissions-related fuel cutoffs)
  • Note the presence or absence of a yellow solid or blinking SES light
  • Scan for diagnostic trouble codes, aka DTCs (1) (2) (3) (4) (5) (6)
    • Write down any "stored" DTCs & do a search for hints (1) (2)
    • Write down "pending" DTCs & do a search for hints
    • Clear all stored & pending DTCs to see if they return in time
  • Reset engine electronics by disconnecting the battery & crossing the cables (with a wrench) for 10 minutes (1)
  • Fill your fuel tank with gasoline from a different gasoline station
If you have a specific-cylinder misfire code:
  • Swap ignition coils between adjacent cylinders (1)
    • If the misfire moves, replace the bad coil) ...
    • Also check your coil harness ground to the valve covers (1)
    • Note: The E39 coils are bolt-down until 8/02 and flip-switch from 9/02 (1)
  • Swap spark plugs between adjacent cylinders.
    • If the misfire moves, replace the spark plugs (0) (1) (2) (3) (4) (5) (6)
  • Swap the spark plug boots (aka spark plug sockets) between adjacent cylinders
    • If the misfire moves, replace the spark plug boots
  • Swap the fuel injectors between adjacent cylinders
    • If the misfire moves, clean or replace the fuel injectors
    • Replace the fuel-injector seals (aka o-rings) (1)
  • Check compression differences between cylinders (1)
    • If the misfire cylinder is lower than the rest, squirt heavy duty oil in the cylinder to check the rings
At this point, we're no longer dealing with specific cylinder misfires.

Multi-cylinder system & specific component tests: (1) (2)
  • Test the engine air filter
    • Temporarily remove the engine air filter
    • If the stumbling disappears, replace the engine air filter
  • Test the Mass Air Flow meter (MAF) (1) (2)
    • MAF faults often set fuel trim faults (1)
    • Temporarily disconnect the MAF & drive the vehicle (1)
      • If the misfire changes, clean the MAF (1)
      • Replace the MAF if necessary
  • Check the hose from the MAF to the engine for leaks
  • Check for a cracked "T-connection after the MAF sensor" or in the air-intake housing (1)
    • If bad, replace the T connection
  • Test the idle control valve (ICV)
    • An overly rich fuel:air ratio can cause the ICV to stick (1) (2) (3)
    • A sticking ICV can lay a coat of soot on the O2 sensors (1)
  • Test the fuel pump
    • Connect a pressure meter to the fuel delivery rail (1)
    • Jump 30 & 87 & feel hoses for fuel delivery (1) (2)
      • If bad, replace the fuel pump
  • Check for vacuum leaks
    • Run the "intake manifold vacuum leak test" (1)
    • Visually inspect all vacuum hoses
      • If any are bad, replace
      • Cracked CCV hose vacuum leaks often affect cylinders 1, 2, & 3 (1)
  • Test or clean the CCV (aka CVV oil separator valve) and its hoses (1)
    • If bad, replace the CCV
    • CCV faults often set fuel trim faults (1)
  • Test the CMP (confusingly aka CPS) camshaft position sensor (1) (2)
    • The CMP will set a fault when it is bad (1)
    • If bad, replace the CMP
  • Test the CKP (confusingly aka CPS) crankshaft position sensor ... (1)
    • If bad, replace the CKP
    • The CKP will set a fault when it is bad (1)
    • The CKP often prevents starting (1)
  • Test the TPS "throttle position sensor" ...
    • If bad, replace the TPS
  • Test oxygen sensors (1)
    • Best way is to scan them for values (1)
    • Pre-cat o2 sensors fail much more than post cat (1)
  • Test the I6 VANOS seals (by disconnecting the harness connector)
    • It's not a bad idea to replace the I6 VANOS seals anyway
  • Test fuel delivery pressure
    • If low, test and/or replace the fuel filter
    • A clogged fuel filter often set fuel trim faults (1)
  • Check the DISA valve for midrange operation
    • Remove DISA valve and check plastic flap for operation (0) (1) (2) (3) (4) (5) (6) (7) (8) (9)
    • Replace the DISA valve o ring (1) (2) (3) (4)
    • Replace the DISA valve if necessary (1) (2) (3)
  • Check the "valve cover gaskets (VCG)
    • Spray carburetor cleaner on while engine is running (1)
    • If idle improves, replace VCG
  • Check the "intake boot" for cracks
    • If bad, replace
  • Check for MAJOR engine problems (usually due to overheating) such as:
  • If you get this far, and you still haven't located or resolved your misfire, you actually now have a bona-fide 'new' problem that has not yet been seen in the Bimmerfest E39 forums!
    • Open a new thread, saying you have a unique misfire!
Here is a misfire-diagnosis video showing the coil swap trick:

Here is a video showing the Brakleen vacuum test trick:

Last edited by bluebee; 05-17-2011 at 07:29 AM. Reason: Constantly edited to add links to diagnostic hints found in other threads
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