Holy mother of misfire's

[Shupe]

New to the world of EFI live. Have been using for about a month now on my 99 5.3 Silverado. Some time after upgrading the OS to an 02 Truck OS 12212156 (at work currently not sure if those numbers are correct) I have began getting random misfires. Initially though it was bad gas or something related. Had seem to come and go. Over the weekend it was became undrivable.

The misfires seem to be random, but ONLY after vehicle comes to temp ~150+ deg. F.

I've tried changing plugs, checking wires / swapping wires, filled up with injector cleaner, ect. Also changed from my slightly modified version of the 02 OS to the unmodified OS. No luck. This morning restored back to the original 99 tune. Was bad enough I had to pull over, pull out laptop and connect scanner.

Just out of curiosity I loaded up the SDAutoVE tune I had just finished in preparation of dialing in the VE. Truck runs great. No misfires. What would make the truck run so terrible while in OL (suspect its in open loop was last time I logged) mode with a map, vs fine while in SD Closed loop mode.

Not familiar with this enough to know what all those changes within the AutoVE Tuturial do.

Any ideas???

[Biggsy]

When in closed loop, the PCM is getting feedback from the O2's and adjusts/corrects the fueling if the VE is out (unless it is way out, then it will struggle) In open loop, the PCM is relying purely on the maps (no feedback from the O2's, so if the VE is out, you will be getting the wrong A/F and can cause problems.

You said you were doing an AutoVE, so I guess you have a wideband?
Log the A/F from WB when it is missing, and log it when it is in CL and not missing and see what the difference is.


BTW, welcome to the forum!! :cheers:

[Shupe]

I do in fact have a wideband. I'll log the differences tonight.. Thanks for the idea.

[joecar]

If it's too lean, it misfires.
If it's too rich, plugs carbon foul, it then misfires.

[Shupe]

Logged on the way to work this morning. Looks as though AFR goes lean up to ~19. Any idea what would cause the AFR to creep up that high.

I've attached the log for the drive into work this A.M.

[Biggsy]

Had quick look at your log and noticed when your actual AFR was 16-17 (even though you're calling for 14.68), the BEN factor was 1.1 - 1.2. looks like maybe VE table not correct

Having said that, your missfire counts are only one one side of the motor
Cyl 1,3,5,7
Intake gasket leak?
Exhaust leak?
O2 sensor problem?

[Biggsy]

Re Read your initial post and thinking because it runs well in OL, I'd say you need to replace an O2 sensor.

Edit: Unplug the O2 on that side (probably will throw a code or two) and see if it makes it run better.

[joecar]

Your NBO2 sensors are not swinging enough nor often.

[Shupe]

Thanks for the ideas...

1,3,5,7 are drivers side bank correct? 1 starting at front?

I have still yet to do the ve test. Want to make sure truck runs well again before start modifying things incase what ever is malfunctioning affects ve test.

I'll unplug this evening and see how it goes. Guess I could swap and see if problem follows other bank. Sensors have 125k on them. Is the slow this a symptom of old 02's? I am running LT's, could this affect the speed of the switching?

Again thanks for the ideas, joecar and biggsy.

[Shupe]

After looking at the log again noticed the NBO2's do not change as often as the WB02, should the NB02 switch as quickly / often as the WB02 sensor?

[joecar]

In CL, NBO2 should swing from below 300mV to above 600mV and back several times per second.

[Shupe]

Swapped sensors from bank1 to bank2 misfires followed to bank 2. Replaced both 02 sensors with new. Can definitely see how the switching was "lazy" while logging before. Back to veTuning....

Thanks for the assistance.