Cylinders Misfiring - Advice sought

[Z8Shawn]

Greetings,

I have a 2000 Z8. 14,000 miles. The vehicle is in excellent condition all around. However, it is 4 weeks out of warranty :(

3 weeks ago I recieved a "service engine soon" light. My local dealer downloaded the computer specifics and learned that "GT-1 test revealed misfires on 5 cylinders (not bank specific)" Evaluated function of catylytic convertors. OK. Checked for intake Leaks. No Leaks found.

They told me that this particular problem most often occurs because the gasoline tank cap is put on incorrectly (not the case with me) or the car has run out of gas (never on my watch). I picked up the car on Thursday (4 days ago). The "service engine soon light" came on again today :eek:

So - the dealer is saying that I need a new catalytic converter for the sum total of $5,000. They say this system fails less than 3% of the time. I am doubtful of their prognosis....

One final bit of background - I recieved a brand new BMW Z8 battery 3 weeks ago after the car would not start due to a dead battery (1st new battery in four years). No other anomolies to report.

Has anyone else heard of this sort of "misfireing cylinder" problem?

Any counsel or insight would be much appreciated, before I buy a new catalytic converter....

Thank you much.

-- Z8Shawn

[macfly]

Not to doubt your dealer, but the problem could also be related to your MAF's in the intake system, which can cause exactly that kind of issue. These units by EPA law have to be warrantied for 100,000 miles, and cost around $1K each. The misfire can be caused by the MAF's putting the motor into limp home mode, something that has been discussed a fair bit over on the m5 board (http://www.m5board.com/vbulletin/forumdisplay.php?s=&forumid=3)

I twice had my first Z8 (July '00 build) go into limp home mode, both times it was caused by a foul up in the AC system termostat which thought the car was overheating. The limp home mode is a caculated constant misfire, and the car will hardly run at all above 4,000rpm.

My suspision is that the Engine Management System is causing this, and they aren't sure why, so they are guessing it's the cats. They are the most expensive part of the system that could be causing the foul up, but also seem to be the least likely to me.

I suggest that it simply needs to be checked by another dealer, and reset once more. If the problem reoccurs you can trace it back to be sure it really is the cats.

Good luck with it, and please do keep us posted. If it is a cat yours will be first one I have heard of failing in our cars.

[Z8Shawn]

Macfly - thanks for the speedy feedback. It is much appreciated. I presented your MAF theory to my dealer this morning, but it seems clear that the car has never gone into "limp home mode" as it still drives great with lots of power across the full range of RPMs and no discernable difference in engine performance: just the yellow "service engine soon" light.

I got a more senior service rep assigned this a.m. and he is going to look at a range of alternative causes for me.

I will certainly share an update once the problem is diagnosed and *hopefully* resolved.

Thanks again for your thoughtful reply.

- Z8Shawn

[Z8Shawn]

After four days with the dealer and a battery of tests, BMW has decided that I do need a new catalytic converter to address the "service engine soon" indicator.

The good news - per the prior posting - is that the Catalytic converter (which of course must be special ordered from Germany and will take many weeks to arrive) is fully covered under the exhaust system warranty provisions :D This is a huge positive development since early discussions seemed to indicate this would not be covered since my original 4 year warranty has passed. The dealer also stated that there is no problem with driving the car while waiting for the new converter to arrive from Europe, although they expect the light will come back on again....

One other clarification: my car never went into limp home mode. In fact, the light coming on was the only indicator of a problem - it continued to run great.

The new catalytic converter will go into the car in approximately 3 weeks and I will post a final update. (with the positive expectation that it will fully address the SES light issue).

Thanks to those who offered thoughts/comments.

- Z8Shawn