muncie21

iTrader: (14)

I've been doing some WOT runs lately and noticed my WB is showing my AFRs bouncing around during WOT. During steady state cruise they don't do this. Also, it doesn't matter if I'm running with the MAF or in SD, they still bounce about .5 to 1 AFR. Can't remember them doing this before. Any ideas???
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JimMueller

iTrader: (9)

It's a bit hard to read all the PID names... the actual log file would help more. Which bank is the wbo2 sensor located? Bank 2 is adding 4% fuel at WOT because of a lean condition in closed loop. What is the AFR you're commanding in that RPM range?

I'd confirm your VE table(s) and/or MAF table are correctly calibrated. Also, only 10* of advance at WOT? I can't read the RPM, but that seems pretty low.

muncie21

iTrader: (14)

Don't know what browser you are using but it may help to click on the image once it loads. My browser automatically resizes the pic for me (geee thanks) to the point that it's practically unreadable.

To answer a few of your comments.
Commanded AFR is 11.01 and actuall is between 11.2x and 12.2x.
I haven't figured out why bank 2 (where the WB is) is running leaner than bank 1. No intake leaks, guess I just chalked it up to disproportional fueling due to rail design.
10* of advance @ 3900 RPM is due to my ride by SC'd. Typically she runs 15* or so, but not more than that.
Regarding the MAF/VE calibration, I can't see the various cells being off so much as to change my AFR by a complete point....but hey, I don't know everything, that's why I'm asking for help

Tomcat

You can see in your narrow band O2 sensors exactly the same thing happening under WOT.

Detonation , misfire , poor fuel mapping , exhaust leak will give the same result. Is the wideband in bank 2 as well ?

muncie21

iTrader: (14)

Yea the WB is on bank 2. I'm logging KR, so I don't think it's detonation...but who knows.

SMOKINV8

iTrader: (6)

I'd look for an exhaust leak, that much detonation would surely trip the KS, and poor fuel mapping would be reflected in the other bank just the same. Maybe a header bolt loosened up enough that it leaks under pressure, but not at light throttle?

white2001s10

iTrader: (4)

It's not because of an exhaust leak... that's for sure.
I think it's likely a mechanical cause though.
It's bouncing towards the lean side. The two most likely causes IMO would be due to a misfire, or surging in the fuel rail.

It is barely possible that it would be a valvetrain control issue, but the first thing I'd test would be the spark plugs. I'd try a new set of colder plugs with about .030" gap and see if it has any effect on the AFR bounce.

The timing is low. Could I assume this is directly due to knock being present and an attempt to avoid it? 11:1 is also very rich to be running with such little advance. Rich AFR's slow the burn. Dropping advance has a similar effect. When you do both to the extreme, you end up with a lot of late burning that can heat up the exhaust valve. A hot valve and extra fuel can cause detonation and/or preignition. It's not as big an issue on bottle cars as it is with boost due to the big difference in intake charge temperatures.
Not to say that people with boost don't run 11:1 AFR with 10* often enough, but there is an issue of heat. Do you see the same exact AFR bounce with a cold engine?

To test the fuel-rail possibility I'd probably up the voltage to the pump to about 16 volts and lower the pressure back to what it was at 14v. Then see if the bouncing is reduced.
If you happen to be running an FMU with your SC, then that complicates matters as the big increase in fuel pressure will reduce the volume capacity of the pump... but you probably already know that.

muncie21

iTrader: (14)

Thanks for all the suggestions. This has all happened after going from stock LS1 heads to stock LS6 heads. Car runs fine and doesn't make any unusual noises.

Usually I run about 15* of timing at WOT. I don't understand why I'm in the 10's and 9's now. I'm logging KR, but it doesn't show on the graph, so something else is pulling the timing.

Regarding fuel pressure, I run a KB BAP with the factory fuel pump. The factory fuel setup isn't boost referenced so I should have about 58PSI on the rail all the time. I'll re-check the pressure tonight.

What I'm really trying to understand is what physical things could possibly cause your AFR to bounce. So far I've heard:

• Misfire
• Air Leak
• Changing fuel pressure

Anything else??

BTW the plugs (NGK TR6) and wires have less than 10K miles on them.

white2001s10

iTrader: (4)

Any valvetrain problem could fall under air-leak or misfire.

muncie21

iTrader: (14)

Did some testing last night.....here's what I found out:

It looks like the WOT AFR spikes are boost related. I changed the requirements to go into PE mode so that I would hit PE well before boost kicks in.

Going into PE under light load and no boost (2nd gear, 35MPH, 2500+ RPM) resulted in a pretty smooth AFR.

Hitting PE under heavy load and full boost (4th gear, 40MPH, 1500 RPM, WOT) resulted in the AFR spikes.

Because of the low engine RPM, I'm pretty sure I'm not fuel deficient. Any ideas of what would happen under boost (4PSI) and high compression (10.5:1) that could cause the AFRs to be unstable?
Here's a screen shot of my log (click to enlarge)

SMOKINV8

iTrader: (6)

It kind of sounds like Jim is on the right track here. What does the scanner show for AFR Error %? I would almost bet your VE or MAF table is not smooth.

muncie21

iTrader: (14)

Thanks for all the help guys. It looks like the higher compression heads were wanting a better set of plugs. I put in a new set of TR6's, ohm'd out all the wires and it looks like things are running better now. It's not as hot as it has been, so the heat could still be an issue.

frcefed98

iTrader: (16)

Cool, looks like you were doing some logging today on I-25/Jefferson? Definately a nice ride man.
J

muncie21

iTrader: (14)

Yup that was me. Doing some runs before I get on the dyno tomorrow to make sure everything is sorted out. If I drove like grandma in front of you I apologize. If I cut you off or did something else stupid, then it wasn't me

white2001s10

iTrader: (4)

So you had a misfire due to a plug or plugs?

muncie21

iTrader: (14)

I'm pretty sure it was plugs or wires. Most likely plugs. I'm guessing the static compression of the new heads was causing firing issues that didn't show up with the stock heads. Either that or a plug wire(s) wasn't all the way on.
Here's what I ended up doing:

• Pulled all plugs to do compression test
• Pulled coil packs and valve covers to check for loose rockers
• Installed new NGK TR6 plugs
• Ohm'd all plug wires
• Installed plug wires

After doing all of that my AFRs under boost are pretty smooth. Also my IATs have dropped about 10-25*F under boost.

frcefed98

iTrader: (16)

Cool, what time are you going to the dyno? Dyno edge or sped dreams?

It was I who cut you off I almost missed my stop because I was too busy watching your vette I was in my work truck Sorry 'bout that

Did your old plugs look fouled or discolored?
J

muncie21

iTrader: (14)

I'll be at DynoEdge @ 10, you're welcome to stop by if you want. You'll just have to swear the super secret oath regarding my final numbers

The plugs looked fine to me, I'm still puzzled by all of this. I'm pretty sure the problem is fixed, but you never know.

frcefed98

iTrader: (16)

Cool i'll see if I can make it. No problems on numbers, I forget em as soon as I see em anyway.

You never know with these cars and their PCMs.
J