Live Data Monitoring with Jscan

[jebiruph]

My JT started getting intermittent P0300 (misc misfire) errors recently and I could tell there were additional misfires occurring that weren't generating errors. So I started monitoring the engine with Jscan's Live Data monitoring to see what was happening and to hopefully get some meaningful data to help diagnose the problem. Following are some screenshots of what I found.

After I got the first P0300 error, I found the discussion of TSB 18-024-21 which calls for replacing the right side (odd cylinders) intake cam if a P0300 occurs. Monitoring cylinder misfires revealed excessive misfires occurring on the odd number cylinders. I presented this information to the dealer (who wasn't aware of the TSB) and left the vehicle there to get the TSB performed.

I kept monitoring after the TSB was completed and had a couple clean trips before the engine problems started back up. After a few additional misfires, I found these pending codes (which never became full errors).

On the drive back to the dealer the next day, all the cylinders were having misfires accompanied with occasional engine surging. The following screenshot was taken as I pulled into the dealer. It also developed an uneven idle as it sat in the dealers service bay.

At this point it's been back at the dealer for a week and I haven't had any updates.

The purpose of this post is to show how live monitoring can help diagnose problems. Following are screenshots of the options Jscan had available for live monitoring.

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[jebiruph]

Since a few misc misfires are not unusual, here's a screen shot of a 30 min combined highway and city drive with a good engine.

 

[Snook]

Since a few misc misfires are not unusual, here's a screen shot of a 30 min combined highway and city drive with a good engine.

Wow, that last image. I never knew engines misfired on occasion like that.

 

[ShadowsPapa]

Wow, that last image. I never knew engines misfired on occasion like that.

Think about it, though. 30 minute drive.
If the average RPM was only 2,000, over 30 minutes, that's 60,000 revolutions.
A 4 stroke/cycle engine fires 1 time every 2 revolutions.
So in 60,000 revolutions of the crankshaft, it is going through a full power cycle 30,000 times in 30 minutes at an average of 2,000 RPM
I think it puts 15 misfires at roughly 5/100ths of a percent if my in-my-head math is right.
And - a misfire can be or mean multiple things. What does the PCM read or regard or count as a misfire? An incomplete burn? A burn that did help power but wasn't up to snuff? A total failure of the charge to ignite at all?
So IMO, 10 misfires in 30 minutes could mean a lot of things - does it count any detonation as a misfire? Did that cylinder ping 2 times in 30 minutes?
I've scoped hundreds and hundreds of engines, had sniffers up their tail pipes, and diagnosed with a dollar bill across the end of the tail pipe or a vacuum gauge and you will see an occasional "hiccup" but unless it's more steady than "now and then", you ignore it, depending on what you see.

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