04 645ci - Misfires, other codes

Car: 2004 645ci - 156,000 miles

What's been done recently (past 2 wks):
New alternator, new battery, new plugs
Back in May, had transmission rebuilt at a highly rated indy trans shop.

What's been going on:
Engine startup (first minute) seems fine. Engine runs good, no codes. After secondary air kicks off, engine rpm drops a bit. After a few minutes, engine rpm starts going up/down, rough idle, and numerous misfires and at times strange clacking sound from under engine. If you wait it out for a while, let the engine come up to temp, stop and restart. everything is fine. drives perfectly, idle is steady, normal engine performance at low/high speeds.

Going on the thought that the replacement alternator might be at issue (or other power issue), I used Carly to log voltages. Second attachment. Left column is voltage and right column is RPM's.

Clearing all the codes after warm up and idling and/or driving for a while throws no more codes. Stop for a while (or long time) and they start coming back again. cycle repeats.

I just made a comment on your other thread. Did you not get a new Valeo alternator?

Bosch alternator

Interesting, was it a Bosch that came of off it? I know the early ones could either have Bosch or Valeo fitted but I'm not sure what the build dates are for each, mine is a december 03 build but came with a Valeo.

That should be a Valeo alternator based on what I have always seen or heard of on a 2004, & 2005 models. I think the 2007 models started using Bosch alternators. What alternator did you remove, & where did you get the replacement from?

The voltage show 2 traces, did you use more than one output? If you can monitor the BSD line, it might help point out if something is wrong. If you start seeing voltage swings above 15.5 volts, I would think the VR could be having problems.

Removed Valeo and replaced with Bosch was from Rock Auto.

Voltage monitor was via Carly for BMW App/Adapter. Readings are from available diagnostic parameters via Carly. Battery Voltage (orange line) and Battery Voltage / AD Converter (grey line).

The data set is not from a "cold COLD" start. Symptoms arise once the secondary air system kicks off and persists until the engine gets to a certain level (temp i'm assuming). So the drop in RPM on that chart @ 22:29 is when the secondary air kicked off. RPM always drops then erratic idle and misfires for a while.

Originally Posted by Kevin645CI2004

Removed Valeo and replaced with Bosch was from Rock Auto.

Voltage monitor was via Carly for BMW App/Adapter. Readings are from available diagnostic parameters via Carly. Battery Voltage (orange line) and Battery Voltage / AD Converter (grey line).

The data set is not from a "cold COLD" start. Symptoms arise once the secondary air system kicks off and persists until the engine gets to a certain level (temp i'm assuming). So the drop in RPM on that chart @ 22:29 is when the secondary air kicked off. RPM always drops then erratic idle and misfires for a while.

The Secondary Air system probably has little to do with this, as it only makes the engine run lean for 30 seconds. It sounds to me that you are talking about the engine running in open loop, verses closed loop. The closed loop is usually triggered by an O2 sensor reaching a certain voltage, along with a temp change from the coolant sensor. This could also be associated with the thermostat.

Was the alternator new or rebuilt?

Rebuilt.

Day job has kept me away from looking at this but finally had the time (and to also get ISTA+ working). Interesting that DIS never showed me a thermostat code but when I switched to ISTA+, low and behold there it is, 00279B DME: Thermostat stuck.

I've got one sitting around and will put it in this weekend but could that be a cause of the misfires and rough idling?

I will cause a rough/ missing idle when cold, but I have not seen a misfire code to be triggered. I am not sure if this answers your question?

Seen a lot of threads on vanos and the related problems when either they go bad or the seals are no good. After a lot of contemplation, decided to give the 'unplug the solenoids' test.

Such a noticeable improvement not just in idle performance but overall engine power.

So I wonder, is there a method to know if the solenoids are actually bad versus just a seal problem? Or just bite the bullet and replace everything?

Since you have them unplugged, test the voltage on each plug. One side should be 12 volts, & the other around 2.84 volts to ground. Turn the key on when doing this. If you don't see that voltage, you likely have a broken wire from heat stress. If the solenoids are not inserted all of the way, you will get all kinds of timing issues. There are 2 different size o-rings on each solenoid, the big one makes it hard to get the solenoid seated some time. A little Vaseline on the o-ring helps getting it back in easier. I usually clean my solenoids with WD40, others use brake cleaner.

So recommend cleaning the ones I have and use new seals?

On a side note, after disconnecting the VANOS solenoids, while everything improved, it wasn't 100%. What ended up smoothing things out to a acceptable level after the fact was doing an adjustment reset. Right now, if it runs good in the morning, I'm done with VANOS for a few days.

The engine is running in a default mode when the Vanos system is not working properly. If you go into the service functions you will see a test for the Vanos system. It will tell you if it is working properly. The MAF also will effect the Vanos system also.

Some say replacing them helps, I have always tried cleaning mine.