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Discussion Starter #1
I apologize for such a long post, but I want to provide as much information as possible about problems first reported on December 4:
http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/168392-constant-idle-hunting.html

In summary, my flex disc was replaced (requiring the exhaust to be disconnected) by my regular shop. After reassembly the idle was surging and there were numerous error codes. The original idle hunting/surging was corrected by replacing the gaskets between the air tubes and plenum. However, the Peake codes 90 (idle control bank 1), cd, ce, ef, and d0 (misfires during warm-up cyl #1 - #4) remained and so I followed suggestions from the board members:

• Installed a new fuel filter and fuel pressure regulator (great write-ups on this board)
• Installed new air filters
• Replaced top hoses of oil separator
• Removed and cleaned oil separators (they were fine)
• Switched right and left MAF’s
• Switched right and left pre-cat O2 sensors
• Switched right and left post-cat O2 sensors
• Searched for cracks in bank one side exhaust

A couple of postings suggested vacuum leaks and I took a gamble and ordered the little plastic elbow under the plenum (which apparently exists only on the LHD cars). Since I wasn’t sure that this was the source of the problem and I was afraid that other vacuum lines and/or connections might need to be replaced, I had my local shop (yes, the same shop) handle the installation. This was a mistake.

They found the plastic elbow was cracked and replaced it along with a couple of generic rubber vacuum lines (at a cost of $638). This eliminated the code 90 and all the bank 1 misfires. However, there were now Peake codes d1, d2, d3, d5 (misfires on bank 2 cylinders)! The car ran very well, but was still turning on the SEL and throwing error codes for bank 2.

The shop did several hours of trouble shooting with and an engine analyzer and smoke generator. Finally, they suggested that I replace the MAFs (which had 25K miles). During the test drive, the SEL popped on and then the car started running rough. The analyzer showed that cylinder #5 was misfiring 1-2 times a second with the same sporadic misfires in the other bank 2 cylinders. The shop owner switched the cyl #5 coil with cyl #7 coil and replaced the plug, but the problem remained. And on a drive back home, the car went into limp mode.

Giving up on the local shop, I took the car to the dealer along with a three page list of the recent history starting with the replacement of the flex disc (and removal of the exhaust system). Of course, they wanted to start from the beginning which meant that they ran the diagnostics and confirmed the errors that I reported. Then, they focused on the high misfire count on cyl #5. The car has been at the dealer for four days and I know that they switched coils (again), replaced the plug (again), replaced the injector, checked the compression (good), switched the DME (good), and “got the foreman involved”.

Most of their time appears to be focused on the one cylinder rather than an underlying problem which causes periodic misfires on all cylinders as well as frequent misfires on one cylinder. So, I am appealing to the experts on this board for suggestions:

What might cause misfires during warm-up on one bank of cylinders?

What would cause a very high count on a particular cylinder (after having only period misfires)?

Why would a fix on a vacuum leak cause the misfires on warm-up to move from bank 1 to bank 2?

Is the problem more likely to be electrical, fuel, or mechanical?

The original problem was caused by (or coincident with) the dropping the exhaust to replace the flex disc, but there has been so much work/investigation (including removing the plenum twice before it was taken to the dealer) another problem could have been introduced. What is the most likely source?

After hours of trouble shooting by my local shop and the dealer, I really can’t expect any of you to diagnose the problem on-line. However, I have been singularly unimpressed with the troubleshooting skills at either location and I am now grasping at straws!

Thanks,

Wayne
 

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Sorry to hear this Wayne.

To confirm:
1. Asking the obvious: did you reset your codes and drive a few times, to confirm re-appearance of the bank 1 misfire-on-warmup codes, after the pinched-gasket replacement?
2. At this point, can you definitively say leaks/cracks along the entire exhaust (presumably introduced from removal during flex disc work) were not introduced?

Beyond that, I would look up members AMP, tradin1 (in your area), vantaam5. That trade of bank 1 warmup misfires for bank 2 running misfires is weird.
 

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Discussion Starter #4
My uneducated gut feeling is that there are two possible reasons that the misfires have moved from bank 1 to bank 2:

1. The vacuum leak probably existed when I took the car in to have the flex disc replaced. (I was getting 23.5 MPG driving 75 MPH on the highway. So, the car was probably running a little lean.) As a result of the exhaust being disconnected and reinstalled, a change was introduced that caused the error code 90 (fuel control bank 1), and the misfires on bank 1 were caused by the DME trying to get the fuel/air mixture correct. When the vacuum leak was fixed, all problems on bank 1 were corrected, but it uncovered a problem for bank 2. I tried to isolate the problem by switching the pre- and post-cat O2 sensors, but was unsuccessful.

2. When correcting the vacuum leak, a new problem was introduced -- a loose clamp, a disconnected wire, a pinched hose, a small item dropped down a throttle, ... After the shop installed the plastic connector in the vacuum line, the errors moved from bank 1 to bank 2. I assumed that the mechanic introduced a problem and removed the plenum myself. Although he did leave the clamp on the hose from the front of the plenum to the block lose, I could not find any lose hoses, clamps, or wires under the plenum.

I have practically worn out my Peake meter clearing codes, and I have reset the DME several times. I think that I have given the DME time to adapt to the new MAFs.

Keep the questions coming!

Wayne
 

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If I just try to think logically about this, a misfire is typically going to be fuel or ignition related. What is in common between both banks (which appear to have experienced issues)? Sooo:

Ignition:
Voltage perhaps to the coils? Grounds as Frits suggest? A common wiring harness?

Fuel:
What about the fuel pump - is the presure and volume adequate? Could a fuel line have gotten pinched, twisted or compressed when the exhaust work was done?

Just thinking out loud...
 

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Discussion Starter #7 (Edited)
Both pre-cat O2 sensors have been replaced.

The coil on cylinder 5 (which is now generating one to two misfires per second) was swapped with cylinder 8 and it did not make a difference. The plug in cylinder 5 was replaced with no change.

The dealer is supposed to check the pressure and flow from the fuel pump, but I'm not sure why that would cause misfires on one bank and not the other, and a disproportionally high misfire count on one cylinder.

I have yet another question: There is a "lambda probe" in the bank 2 exhaust. What is the function of this probe?

Wayne
 

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By lambda probe I guess you mean the exhaust gas temp sensor in the bank 2 exhaust system.



Regarding the mis-fire in cylinder 5,it is either the coil connector,the ground wiring,the wiring of the coil from the ECU to the coil.

The injector on cyl.5 was changed,right?
 

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Discussion Starter #9
The BMW parts catalog calls it a "regulating lambda probe," but I have no idea what it is regulating. I just know that it has never been replaced and is attached to the bank 2 exhaust!

The dealer wanted to replace the cylinder 5 injector. I voted against it because all the bank 2 cylinders were misfiring. However, they are the pros while I'm an armature and the injector was replaced. I would have been happy to be wrong, but the new injector didn't reduce the misfires on 5 or any other cylinder.

I am going to try to talk to the service manager tomorrow and request that they:

- try to focus on a solution that would impact all cylinders n bank 2
- check the ground wiring and the wiring from the EUC to coil
- contact BMW support for advice

You would think that BMW would have large datebase of problems/solutions for a 10-year old car even when it is a low production model. Additionally, I worry about new problems being introduced as mechanics take things apart and swap components.

Thanks for the suggestions,

Wayne
 

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Discussion Starter #11
You were right the first time! I was mis-reading the parts catalog. I have never replaced the exhaust gas temperature sensor!

Does this sensor send data to the DME? Could it confuse the DME if it wasn't working correctly or not working at all?

Sorry for the confusion,

Wayne
 

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The sensor is NLA,BMW updates the ECU software as facelift cars do not use it anymore.

Its primary function is to monitor the exhaust temp.The data is used by the ECU to add fuel if the Cats get too hot to cool them down.

Not likely this is your issue..
 

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Discussion Starter #14
Vantaam5, thanks for the advice on the exhaust gas temperature sensor. I would be happy to eliminate this part as a source of my problems without having to purchase a new one!

E55AMG2, the crossed cat O2 senors was suggested when my problem first appeared in December. The sensors were rechecked at that time, but I'm not sure that they have been checked since the misfires moved to bank 2. I don't know how they would have been switched, but I'll add this to the to-be-checked list.

Wayne
 

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Vantaam5, thanks for the advice on the exhaust gas temperature sensor. I would be happy to eliminate this part as a source of my problems without having to purchase a new one!

E55AMG2, the crossed cat O2 senors was suggested when my problem first appeared in December. The sensors were rechecked at that time, but I'm not sure that they have been checked since the misfires moved to bank 2. I don't know how they would have been switched, but I'll add this to the to-be-checked list.

Wayne
Sometimes they get mixed up, as the connectors are the same. Hopefully it's something simple like that.
 

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Discussion Starter #17
I’m sorry that I haven’t provided an update or answered questions over the past few days.
However, my car has been at the dealer and I couldn’t pursue any suggestions. After
spending 10 days there, I picked the car up today.

Here is a summary of their tests and results:

- Interrogate fault memory; showed misfires on cyl 5, 6, 7
- Cleared memory and drove the vehicle. Found misfire counter showing #5 over 2000 times #6 90 times
- Focused on #5 and swapped coils and plugs – no effect
- Performed compression test on all 8 cylinders – numbers within normal range
- Performed leakdown check on #5 – less than 5%
- Checked coil for spark – spark good
- Removed intake manifold and swapped fuel injectors – no effect
- Verified injector operation with stethoscope
- Swapped DME and EWS from donor vehicle – misfires still in #5
- Inspected inside combustion chamber with bore scope –found no abnormal wear or valve damage
- Removed valve cover to inspect valve train – nothing found
- Checked that the throttle linkage was setup correctly – within specs

The mechanic feels that cylinder #5 is getting fuel and spark, but is dead, and the other bank 2 misfires are simply “misreads”.
At this point, the dealer said that the problem must be mechanical and they would have to remove the head to continue the
investigation. The removal and reinstallation would be $4300 and this did not include the repairs to correct the problem.

I am at a loss for suggestions, but my gut still believes that the problem is not mechanical. If the leak down test had
been bad or the bore scope showed some damage, maybe I would purse this tract. But there is no way I am going to
pay $4300 plus some unknown (and large!) amount unless there is a strong indication that the problem resides here.

Here are a couple pieces of anecdotal information. First, on the drive home the car definitely acted like it had a dead
cylinder, but it ran worse when I drove the car into the shop. Sometimes the car runs worse than at other times and
there doesn’t seem to be a correlation to any observable data.

Second, I cleared the Peake codes after picking up the car. After a 20 minute drive home I had the expected misfires in
cylinders #5 and #6, but I also had misfires in #3. (This is the first time that I have seen a misfire in a bank 1 cylinder.)
With the Peake reader, all I can get is the codes; I can’t get counts.

I’ve pretty well exhausted my ability to test scenarios, but I am still open to suggestions – even if it means going back
where I fear the problem was introduced. They have test equipment and some expertise.

BTW, the BMW dealership claimed that they only receive tech support from BMW on cars under warrantee and there is
really no “problem/solution” database. Is this true?

Wayne
 

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Discussion Starter #19
I saw the mechanic at my shop replace the plug in cylinder #5 with one from the box and switch the coil with the one on cylinder #8 and it had no effect.

The mechanic at the deal wrote (I didn't see it) that he "swapped the coil and plug", but I don't know where he got either of them.

Is the M5 like old cars where you coluld remove the plug and watch it fire?
 

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is it possible a bad vanos solenoid could be causing the misfires? i know I had plenty when my board went.
 
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