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Old 11-21-2010, 09:51 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 20,512
Mein Auto: 02 BMW 525i M54 auto 130K
Here's my attempt at GENERALIZING that procedure for use by others.

BACKGROUND:
A) If a misfire occurs more than once in 200 revolutions in any one cylinder, the engine computer (DME) cuts off fuel for that cylinder's nearby injector in order to protect the emissions system;

B) A DTC diagnostic trouble code is thrown indicating the cylinder(s) that misfired and that the fuel was subsequently cut off & the SES service engine soon malfunction indicator light (MIL) comes on solid yellow (not blinking if it's only once in 200 revolutions) to warn the driver of the problem;

C) Even if the misfire no longer occurs, the fuel cutoff is "permanent" in that it is only corrected upon the next ignition cycle (or by manual clearing of the DTC with a diagnostic tool if, for some reason, the vehicle is kept running).

D) The SES remains lit for about 50 miles and 3 starts; but the DTC should remain stored for longer than that (how long?).

Theoretically, if an engine isn't running, it's ALWAYS one of the following requirements:
a) Gas, b) Air, c) Spark, d) Timing, e) Compression

More specifically, a precise fuel:air ratio must be ignited at the right time with enough compression to explode. So, all misfires, somehow relate to one or more of those five fundamentals being skewed.

Specifically, here's what to look for (somewhat in this order based on an anecdotal survey of misfire threads):
  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 [air:fuel ratio]
  6. bad coil packs [spark]
  7. bad coil boots [spark]
  8. bad or ill fitting spark plug valve cover seals [spark]
  9. worn or fouled spark plugs [spark]
  10. bad mass air flow (MAF) sensor or meter [air:fuel ratio]
  11. bad DISA valve flap [air:fuel ratio] (1)
  12. bad DISA valve o-ring [air:fuel ratio] (1)
  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. cracked rings [compression]
  17. bad camshaft position sensor CMP, aka CPS [spark? timing?]
  18. bad crankshaft position sensor CKP, aka CPS [spark? timing?]
  19. bad ground wires [spark]
  20. bad fuse or relay [gas, spark, timing]
  21. bad electrical wiring [gas, spark, timing]
  22. bad engine computer DME, aka ECU [spark]
  23. intake manifold gasket leak [compression, air:fuel ratio]
  24. bad crankcase oil separator valve CCV, aka PCV [air:fuel ratio]
  25. bad idle control valve ICV [air:fuel ratio]
  26. bad throttle position sensor TPS [air:fuel ratio]
  27. bad VANOS seals [compression, air:fuel ratio]
  28. head gasket leak, or a cracked block [compression, air:fuel ratio]
However, that list above is NOT a debugging algorithm!

What we need is an E39 engine misfire debugging algorithm (here's a start):
When you notice a BMW E39 engine stumble ... it's always either gas, air, spark, compression, or timing; so concentrate on factors that affect those 5 requirements!
  • If you're misfiring, immediately shut off the ignition
  • Wait 30 seconds before restarting the engine (this resets emissions-related fuel cutoffs)
  • Note the presence or absence of a yellow solid or blinking SES light
  • Scan for diagnostic trouble codes (DTCs)
    • Write down and DTC and Google that DTC for hints
    • Clear all stored 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 (8)
  • Swap spark plugs between adjacent cylinders.
    • If the misfire moves, replace the spark plugs
  • Swap the spark plug boots between adjacent cylinders
    • If the misfire moves, replace the spark plugs
  • 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.
Now we start handling specific component tests, repairs, & replacements:
  • Temporarily remove the engine air filter
    • If the stumbling problem disappears, replace the engine air filter
  • Temporarily disconnect the MAF & drive the vehicle (1)
    • If the misfire changes, clean the MAF (replace if necessary)
  • Clean the MAF & check the hose from the MAF to the engine for leaks
  • Check for a cracked "T-connection after the MAF sensor"
    • If bad, replace the T connection
  • Test the fuel pump by jumping 30 & 87 & feeling hoses for fuel delivery (1) (8)
    • If bad, replace the fuel pump
  • Clean (or replace) the mass air flow sensor (1)
    • An overly rich fuel:air ratio can cause the ICV to stick (1)
    • A sticking ICV can lay a coat of soot on the O2 sensors (1)
  • 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
  • Test the CMP (aka CPS) camshaft position sensor (1)
    • If bad, replace the CMP
  • Test the CKP (aka CPS) crankshaft position sensor ...
    • If bad, replace the CKP
  • Test the TPS "throttle position sensor" ...
    • If bad, replace the TPS
  • 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, replace the fuel filter
  • Clean the MAF and check the hose from the MAF to the engine for leaks or tears
  • Check for a cracked "T-connection after the MAF sensor"
    • If bad, replace
  • Check the "valve cover gaskets (VCG)
    • If bad, replace
  • Check the "intake boot" for cracks
    • If bad, replace
  • In addition to pious pleas to the Lord Jesus, go ahead, add a bottle of Seafoam or Techron concentrate to the fuel
Here is a video testing for vacuum leaks by spraying carburetor cleaner on hoses:

Last edited by bluebee; 01-17-2011 at 10:03 AM.
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