Closed Loop Misfire, What's To Blame?

[Supercharged111]

So my truck's had this intermittent misfire since last fall and I can never seem to pinpoint it. It has new AC Delco iridium plugs, AC Delco cap/rotor/wires/distributor gear and CMPRET is at 2 or 3. It clears up before I can even begin to diagnose. It's made the truck so gutless I can barely make it home after I blew through a puddle or today when I may have had some coolant flying around due to a leaking QD in the intake. I've also seen the MIL flash when I'm running WOT through 2nd either to climb a hill and pass as many assholes as possible, or because I'm pulling my trailer up a hill. Today I was datalogging and tuning for the new to me marine cam and 1.6:1 roller rockers I installed. The truck was coming along nicely and then it started breaking up. My first thought was just to get the damn thing home. I was maintaining about 55mph in 3rd gear, that was the beans until I hit a hill. I matted it and crossed my fingers, much to my surprise the truck snapped to life like nothing was wrong and I'm sure the guy who had been tailgating me was probably going WTF. My thought was that the added PE fuel must have been just what the truck wanted, so I reached over and flicked off closed loop with the bidi controls. Voila, truck runs normal again except now it's really showing where the truck wants more fuel. Even the idle settled down and acted normal again. So are my O2 sensors to blame or is this an indication of something else? A few months ago, it was flagging the MIL for a slow to switch O2 sensor but after a road trip that went away and hasn't come back. I'm thinking I'll inspect the extension harnesses and try to track down any grounds I may have neglected to reinstall with the heads having to come off. Someone mentioned a weak coil doing this too as a lean mixture is more difficult to light. I thought it was just that the flame speed was slower though.

[joecar]

Sounds like NBO2's...

Do you have a log of HO2S11 and HO2S21 and LTFT1/2...?

[Supercharged111]

Yes cam log 3 is the one where it acted up and I switched to open loop, but I included cam log 4 as well. Cam log 4 is where I ran open loop from the house to pick up my trailer and cringed at the AFRs with the more aggressive timing map I had just built.

18162

18161

[joecar]

It looks like MAP is pegging at 75 kPa @ WOT, are you at 3000' altitude...?

At idle your MAP has some strange oscillations with ~25 second period, these also show up in CYLAIR but not in MAF.

Something might be wrong with MAP, you need to test it with a vacuum pump (Mityvac).

Judging from MAF pegging out at 184 g/s @5100 rpm @ WOT, either air filter is clogged or MAF is failing.

Also, this happens when HO2S21 starts to peg at 1100 mV @ light throttle... possibly the NBO2's have to be replaced.

[joecar]

HO2S21 pegs at 1100 mV.

MAP still pegs at 75 kPa.

[Supercharged111]

MAP/MAF are limited due to my elevation here, 6200'. So my O2s adding fuel aren't because I haven't tune VE/MAF? I kind of thought that was the deal with LTFTs being what they were.

[joecar]

( lol, my calculation was off by factor or 2 )

HO2S21 pegs at 1100 mV during CL, something is wrong with it (compared to HO2S11 which continues to cycle)... this causes LONGFT2 to remove fuel (this is what I meant to say).

So the VE/MAF tables are not tuned/corrected...?

[Supercharged111]

( lol, my calculation was off by factor or 2 )

HO2S21 pegs at 1100 mV during CL, something is wrong with it (compared to HO2S11 which continues to cycle)... this causes LONGFT2 to remove fuel (this is what I meant to say).

So the VE/MAF tables are not tuned/corrected...?

Fuel isn't tuned yet, no. I was primarily working on the timing table below 2500 in the cells I hit in OD to make it more resistant to a downshift. I'm still working up the motivation to do a CALC.VET as I've not yet performed one. LTFTs looked pretty good on my map, usually within 3%, so I figured it was safe to go after timing in the areas where the O2s can still do their thing. How are you seeing where the O2 hangs up? Did you just hit play and watch the dashboard or is there another part of the scan tool I should be utilizing?

And just to be clear, isn't 1100mV considered out of range for a NBO2?

[400ss]

This problem with the o2s pegging at 1000-1100 just happened to me like 1 week ago. Changue o2s . Delete learned trims.

[joecar]

I zoomed in to various parts of the log... you will see LTFT2 making some negative zigs, and here you will see HO2S21 pegging.

[Supercharged111]

New O2s will be here Thursday, I'm open loop until then. Watching the wideband you'd hardly know it. Joecar can you post up a screenshot of what you're talking about? I mostly use the data, dashboard, and maps tabs. It sounds like you're talking about something different.

[400ss]

Hes talking about instead of using dashboard it shows you the info like in graphic form. I dont know how to explain myself, dont have those words in my bad english

[Supercharged111]

It's a black background with lines being the data, right? How do I get it to display like that?

[joecar]

This is one of the places I zoomed into (see pic).




( also here is the dash I'm using )

[Supercharged111]

Awesome. I've got to suspect that's one of the default dashes to choose from now, never knew it was the dash though and could never see a good use for it until now. I'll use that to search for that MAP anomaly you referenced on the first page.

[Supercharged111]

So I just realized you can have 3 dashboards rocking. I've been trying to get to the next level on this software, this was also my first use of the bidi controls. Really cool stuff. Thanks for all the help!

[joecar]

Awesome. I've got to suspect that's one of the default dashes to choose from now, never knew it was the dash though and could never see a good use for it until now. I'll use that to search for that MAP anomaly you referenced on the first page.It's a dash I made up for my purposes...

[joecar]

So I just realized you can have 3 dashboards rocking. I've been trying to get to the next level on this software, this was also my first use of the bidi controls. Really cool stuff. Thanks for all the help!Not only can you have 3 dashes (A, B, C), but on any of those you can have a mix of gauges and/or charts together...

[Supercharged111]

I meant that the style of dash you posted is probably a default, I noticed the grouping and coloring of your selected PIDs and that there was a good deal of thought put into it. So is that called a chart then?

[joecar]

I color code particular pids on the chart to help me analyze.

Yes, a graph-vs-time is referred to as a chart in EFILive terminology.

[statesman]

Not only can you have 3 dashes (A, B, C), but on any of those you can have a mix of gauges and/or charts together...

Have any instructions been posted on how to mix gauges and charts together?

[joecar]

The scantool user manual has some info (on a dash pages you basically go rightclick and go from there).

[statesman]

(on a dash pages you basically go rightclick and go from there).

I just had a quick play with it and it works for me... thanks.

[Supercharged111]

Thought I'd add some rather obvious closure here, new O2s in truck runs normal. I do need to run a calc.vet though, I suspect VE is quite close and it's the MAF chart that's to blame for PE fueling being leaner than commanded. I'll see soon enough, the procedure looks pretty cool seeing how you can just leave CL on and you don't have to disable PE.

[joecar]

Dustin,

In this screenshot you will see the MAP oscillations we talked about...

MAF, RPM and TP are steady (TP is closed);
SPARKDADV is almost "steady" (its rapid corrections do not align with the MAP oscillations)

[Supercharged111]

Hmm, MAP goes up and takes spark up with it? Odd. Hopefully it's that gasket randomly leaking and not leaking. Looks like I'm open loop at this point so I'm most likely idling at a red light on the way home. What I find most intriguing is the way TP appears to fluctuate too. I assume this is just a 30 second screenshot so it's doubtful that I was actually getting in and out that quickly to creep up to said red light. I'm going to have a look at this section of my log when I get home and compare it to any other oscillations I may have written off. Thanks for revisiting Joe.

[joecar]

Maybe there's a loose ground somewhere...

[Supercharged111]

I've considered that, there is 1 that I feel I didn't clean enough. It wasn't rusty, but it was oily/greasy/grimy. That one on the back of the head though is immaculate, I saw to that before I reinstalled the head. Dealer never ordered my MAP sensor seal, so I get it tomorrow and not today. A Friday cold start should validate whether or not that is the fix action. With the junkard sensor goobered up with not enough silicone, the truck randomly runs stronger that it ever has so my hopes are up. I was able to drag my trailer with relative ease compared to before, but there does exist the possibility of a random tailwind following my north, west, east, and then south just to screw with me.