Durametric shows cylinder misfire counts - what's normal?

[mchung]

Hi all,

My '06 CS has some slight roughness when accelerating at low revs ~1500 RPM (dealer says I shouldn't be running the engine that low, but if the automatic tranny allows me to drive at those revs and gear combination....). Should a properly running CS be smooth?

There's no CEL being raised and all codes are clear. However, the Durametric software is showing Misfire Counters values of 0 and 1 and sometimes up to 4 on all cylinders when I look at the Motronic Actual Values while the engine is running (some cylinders are worse than others). Most of the time they appear to be 0.

What I wanted to know before I approached the dealer was whether a properly functioning engine will occasionally detect misfires anyway as part of normal operation. If not, then I think I have a better case for them to diagnose what I think is the infamous coil issue.

Thanks for the help and other thoughts!

Martin

[Loren]

Have your ignition coils been replaced?

My guess is you have one more that are cracked.

[wvicary]

This is a good question. I also have monitored misfire counts over the years and have found several engine that count misfires but only in the single digits and never trigger any codes or worsen. Sometimes it's only one cylinder or several and you can not feel the misfire while driving or at idle. Only when the misfire count gets into the high tens or low hundreds in a short amount of time while it be felt or trigger the light. I've concluded that it's nothing to worry about unless the DME actually sets a code.

[mchung]

Yeah, I guess it's really how many in a certain period. It also looks like the DME holds on to a value for a few seconds and then resets the count again, so that can have the effect of overreporting the totals if I just add up the numbers. The numbers get up to a maximum of 4 before they reset back to zero.

When I run the logs through Excel and simply add up the numbers, I get a total of 1000+ total events over an 18 minute driving period, the highest cylinder being up to 236, the lowest being 51.

I've only owned the vehicle since October and I don't know the past history. I'll probably pop under the hood to check the coil part numbers.

Cheers,

Martin

This is a good question. I also have monitored misfire counts over the years and have found several engine that count misfires but only in the single digits and never trigger any codes or worsen. Sometimes it's only one cylinder or several and you can not feel the misfire while driving or at idle. Only when the misfire count gets into the high tens or low hundreds in a short amount of time while it be felt or trigger the light. I've concluded that it's nothing to worry about unless the DME actually sets a code.