Tracking misfires -Torque Pro

[candem]

On a recent trip the engine started misfiring. Managed to get it back home and then started dooing some research. It had a P0300 code as well.

Found various threads on here about tracking misfires using Torque Pro so I set that up to monitor realtime and history. Sure enough cylinder 4 had about 59,000 historical misfires. Changed the coils on 3 and 4 and then cylinder 3 was misfiring.

Figured I was better off replacing all coils so ordered a set from Amazon. price for the set was the same as one coil from the local auto shops - around $65.

I have installed them and have a question on the misfire data. I am seeing consistent occasional misfires across all the cylinders in realtime. Typically this shows as a "1" or a "2" for that cylinder. These are however not beeing added to the historical misfire data. Here is a screenshot of what I setup:


So my question - is this normal or should there by zero misfires?
If not normal, any suggestions on what I should be looking at?
Vehicle does have 225k and sparkplugs are ACDelco and approx 50k miles old.
Thanks.

 

[Blckshdw]

I am seeing consistent occasional misfires across all the cylinders in realtime. Typically this shows as a "1" or a "2" for that cylinder.

So my question - is this normal or should there by zero misfires?

I've been using Torque pro for years, and the misfire data has always been screwy for me. My false misfire reporting is a bit more extreme than yours, I'll randomly have a cylinder blast out hundreds of misfires, but no CEL and the engine is running fine.

Get to a destination, do what I have to do, get back in the truck, and a different cylinder goes crazy. I don't have them on my display anymore, because of it. So in your case, I think you don't have anything to worry about.

 

[Mounce]

I figure it's got to reach a certain threshold for the pcm to believe it. Figure it detects misfires off of crank angle vs upstream o2 reading (or does it see cylinder contribution by rpm fluctuations? I can't remember it's one of those vs crank location). Anyways what I'm trying to point out is that this is an extremely precise amount of data studied to give a misfire count. Fuel amount in cylinder, iat, spark, and many other things can throw off how combustion takes place in one cylinder compared to others when considering uneven carbon deposits and varying age and condition of plugs and coils.

I wouldn't read too much into a misfire counter unless you're feeling or hearing a miss. At that point the computer will count the accurate misses until its threshold is reached to start throwing codes. Once it reaches that threshold of being sure of what it's seeing current misfire counter should be climbing by the revolution and adding to history.

This is my understanding of how this feature works, it may or may not be 100% correct but this is what makes sense to me from what I've learned and seen in the field. Don't discredit the scantool sample rate adding variables as well, a high end scanner will see things different than a scanner going through a Bluetooth connection and an app on our varying smartphones.

 

[mrrsm]

The first clinical observation that will beg for examining a very wide array of possible causes for this issue... is that your 2002 Chevrolet Trailblazer has 225,000 Hard Miles on the Drive Train.

Given the age of your vehicle... the Torque APP might be considered an interesting Tool available inside your Tool Chest ...but it is NOT THE Tool for solving all problems. Mechanical Wear on Older Engines demands using Mechanical Test Equipment to dig deeper in these matters.

This is an On Topic Video that will expand on the Causes and Solutions for P03XX Codes in deep detail and provide you with excellent explanations of these issues... regardless of the Engine Designs being investigated:

 

[TJBaker57]

For the seriously curious....

 

[budwich]

Quote: "On a recent trip the engine started misfiring. Managed to get it back home and then started dooing some research. It had a P0300 code as well.

Found various threads on here about tracking misfires using Torque Pro so I set that up to monitor realtime and history. Sure enough cylinder 4 had about 59,000 historical misfires. Changed the coils on 3 and 4 and then cylinder 3 was misfiring."

I think that is what the pid's are for... kind of help direct your attention to a troubled area. Beyond that, as was suggested, potentially "light misfires" are probably not much of concern unless they continue on a certain cylinder. As for historic versus current, I believe historic only get updated during the next start cycle while current are "pegged" during that cycle. You "played" with 3 and 4 so those counts appear to correlate that activity. There may be some concern around 5 but since you replaced all the coils, maybe the "soft issue" has gone away.

 

[Mooseman]

When you replaced the coils, did you also replace the plugs? If so, did you use real ACdelco 41-103? (there are fakes out there). This engine is sensitive to the plugs you use and can cause misfires. New plugs may help with the odd misfire here and there.

My 4.2 in the TB has a weird misfire issue. It will misfire on #4 while idling but nothing while driving. If I let it idle long enough, it will eventually throw a P0304. Never been able to figure that one out. In my old EXT, it never misfired except when a coil would die. The 5.3 in the Saab has 0 misfires. Who knows if the crank sensors in different engines have different sensitivity as it detects the RPM change on misfiring cylinders. A CASE relearn might help or possibly a new sensor.

 

[Kelly@PCMofNC]

I probably wouldn't worry about 1-2 misfires per cylinder randomly, with that mileage.