Bimmerfest - BMW Forums - View Single Post - How do diagnose a sudden and disturbingly unsettling cold-engine misfire (vanos?)
View Single Post
Old 11-21-2010, 08:39 AM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by redidrum View Post
All new plugs, coil packs, and boots. ...I'll try to make the exhaust cam position sensor fit the intake.
Let us know how it works out.

I just made a summary in yet another cold-engine misfire thread, so I figured I'd summarize what is said in this thread here below.

In my case, this was the presumptive misfire scenario:
A) Misfire occurs more than once/200 revolutions in one cylinder, so that DME cuts off fuel for that cylinder's nearby injector;

B) A DTC diagnostic trouble code is thrown indicating the cylinder that misfired and that the fuel was subsequently cut off & the SES service engine soon light comes on solid yellow (not blinking) to warn the driver;

C) Even if the misfire no longer occurs, the fuel cutoff is only corrected upon the next ignition cycle (or 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?).

And, here's what lild said to look for
1--bad fuel
2==trash or gunk in fuel
3---spark plug valve cover seals
4---head gasket leak, or cracked block
5---bad spark plugs
6==bad coil pack or boot (Bentley says to diagnose with an oscilloscope)
7---bad 02 sensors
8---bad maf mass air flow sensor or meter
9---bad fuel injector
10---cracked ring
11---cam shaft sensor cps
12==crank sensor cps
13---bad ground wires
14--- bad fuse or relay
15---bad electrical wiring
16--- dme, or ecu (Digitial Motor Electronics, i.e., the engine computer)
17--intake manifold gasket leak
18--ccv--aka pcv, crankcase oil separation valve
19--icv--idle control valve
20--tps==throttle position sensor
21-- bad VANOS seals

Here's the algorithm I gleaned from reading everything I could in bimmerfest on the topic (before the above two summaries were made):
0. When you notice a BMW cold-start stumble ...
1. Shut the ignition off & wait 30 seconds before restarting
2. The stumble may go away but look for the SES light on the cluster which should remain
3. If you see an SES, check for a P1349 code and reset the MIL
4. If you have a P1349 code, swap ignition coils between #3 & #4
5. If the intermittent start stumble moves to cylinder #3, replace the coilpoolman coil recall information here)
6. If the start stumble returns on cylinder #4, swap or replace the plug
7. If the stumble returns on cylinder #4, swap or replace the plug boots
-----< after this point, I think we're moving away from the specific cylinder >-----
8. If it returns on cylinder #4, clean the MAF (hot film air-mass meter) with CRC & replace the air filter
9. If it returns, replace the "cam position sensor" (is there one specific to cylinder #4?)
10. If it returns, replace the Cam Position Sensor CPS (is this specific to cylinder #4?)
11. If it returns, replace the post-cat oxygen sensor (the pre-cat 02 sensor is not implicated)
12. If it returns, replace the VANOS seals (can variable valve timing affect only a single cylinder?)
-----< after this point, we're really shooting in the dark >-----
13. If it returns, replace the CCV (aka CVV oil separator valve)
14. If it returns, replace the fuel filter (one guy suggested replacing the fuel pump)
15. If it returns, add a bottle of Seafoam or Techron concentrate to the fuel
16. If it returns, clean the ICV (idle control valve) with carb cleaner
-----< people really suggested all these items in the respective threads
17. If it returns, replace the hose from the MAF to the engine
18. If it returns, replace any cracked "T-connection after the MAF sensor"
19. If it returns, replace the "valve cover gaskets (VCG) into the spark wells"
20. If it returns, clean or replace all the fuel injectors
21. If it returns, replace the "coolant temperature sensor"
22. If it returns, replace the alternator to raise the voltage (yes, this has been suggested)
-----< ok, these were listed as solutions but they aren't feasible >-----
23. If it returns, move to Georgia (from Michigan
24. If it returns, drive the car every day (don't let it sit for two days)
25. If it returns, check the "intake boot" for cracks and replace if necessary
26. If it returns, replace the "throttle position sensor" (TPS)
Note: Don't laugh; I've read dozens of threads and each of these has been posited as the "solution" to this intermittent problem!

Last edited by bluebee; 11-21-2010 at 08:40 AM.
Reply With Quote