Commanding AFRs I didnt command?????

[Liltroy]

2006 LQ4/4L80 swap with BTR stage 3 truck cam.this was my first attempt at tuning and I have been playing around with it for several months now.I tuned in SD first, got all my AFRs straight, then tuned the Maf and all AFRs were pretty straight. Today I decided to combine them and turn everything back on. LTFTs look ok so far and the truck seems tto be running smoothly but Im having a weird issue. Im commanding 14.68 over all and 12.9 at WOT but sometimes while cruising at a steady speed it will all the sudden start commanding w=either 16.0 or 13.61????? I dont understand why this is happening but when its doing it, the only way to "break it out" of that commanded AFR is to floor it. Slight throttle adjustments wont cause the commanded AFR to go back to what its suppossed to be and only leads to lots of KR when its commanding the 16.0. Anyone have any clue whats causing this? Current tune and last Datalog are attached. Thank you for any help gentlemen.

[mowton]

It looks like the rear 02s test...PCM drives commanded rich and then lean and it measures the rear O2 values to determine if they are working or not......

Ed M

[Liltroy]

It seems to be doing the opposite. It makes it go lean for awhile then rich. How do I make that stop?

[5FDP]

Plug the rear o2 sensors back and zip tie them away.

It's a cat test HPT cannot shut off, only way to stop it is to plug the rear sensors back in.

Side note, your VE and MAF need a little more work. Pretty choppy in both and your way out of injector. You maxxed those things out and then some, you are seeing over 105% duty cycle.

[Liltroy]

I know the tables are choppy but if I smooth them out at all then my afrs are out of whack. With them choppy, my afrs stay where they're supposed to be so my choices are smooth tables with up and down afrs or choppy tables with correct afrs. After weeks of trying to smooth them, I decided Id rather have my afrs straight than to have baby smooth 3D graphs, lol. As for the injectors, Im trying to find a cheap option for the injector upgrade but currently out of cash and cant seem to find anything plug and play for less than $300.
So back to the weird afrs.....youre telling me theres nothing I can do about this? cause getting all that knock retard during part throttle transitions from a steady cruise seems kinda dangerous. And it only does it when its in that 16.0 afr crap.

[5FDP]

Perhaps how you are tuning it is leading to the choppy tables. I used a wideband AFR error for tuning and manually smooth the tables after the changes to keep everything in line.

Find some 8.1 vortec injectors for cheap, they are rated at like 31lb and should give you plenty of room if you aren't going to mod much further.

As for the commanded air fuel swings, I dealt with the same exact thing on my old 2006 GMC Sierra. I removed the o2's with the aftermarket off road y-pipe and my wideband always showed the swings, then I hooked my laptop and saw the changes it was doing on it's own. With reading and searching the issue the only solution is to re-install the rear o2 sensors because you can't disable the cat test. It took my all of 5 minutes to plug them back in and zip tie them up and out of the way. Never had a single problem after that.

[Liltroy]

ok so I was just on a forum where a guy was having a similiar issue and was told to set the rear O2s to error with no MIL so that the pcm would would not try to test them due to seeing they were already failed. Does this work?

[Liltroy]

Perhaps how you are tuning it is leading to the choppy tables. I used a wideband AFR error for tuning and manually smooth the tables after the changes to keep everything in line.

Find some 8.1 vortec injectors for cheap, they are rated at like 31lb and should give you plenty of room if you aren't going to mod much further.

As for the commanded air fuel swings, I dealt with the same exact thing on my old 2006 GMC Sierra. I removed the o2's with the aftermarket off road y-pipe and my wideband always showed the swings, then I hooked my laptop and saw the changes it was doing on it's own. With reading and searching the issue the only solution is to re-install the rear o2 sensors because you can't disable the cat test. It took my all of 5 minutes to plug them back in and zip tie them up and out of the way. Never had a single problem after that.

ok so I just need to find a set of rear O2s to plug in then. That seems simple enough. Thank you!! As far as the tuning, Im using a Wideband as well but like I said...if I try to smooth the tables out, them on my next drive, the cells I changed to smooth it have to be changed back for the afr to be +-1 so it just ends up choppy again. This is why its taken me so long to finally finish...because I was constantly smoothing, then having to change it back. I bet I made over 60 drives and went through 3 tanks of gas before I finally decided to just leave it where the AFRs were right but table was choppy.
Ive heard that those 8.1 injectors are a nightmare to tune because no one seems to have the correct data on them???? Do they plug into everything without modification? and where can I get reliable injector data on them? I ask because I have a cousin with a blown up 8.1 that I could probably get the injectors off of for a 12 pack.

[5FDP]

Something must have been skewing your data if the AFR kept changing that much after each change. Maybe the MAF wasn't 100% failed in the tune and you were still logging it or you had the fuel trims screwing it up. Even correcting too much and over shooting too, I always do special paste by half for VE and MAF tuning. Should only take a few hours to get things dialed in.

Find a 8.1 vortec tune from the repository and copy the data straight over.

Anything from like a silverado/suburban/avalanche all came with the 8.1 in the early 2000's.

[Liltroy]

Something must have been skewing your data if the AFR kept changing that much after each change. Maybe the MAF wasn't 100% failed in the tune and you were still logging it or you had the fuel trims screwing it up. Even correcting too much and over shooting too, I always do special paste by half for VE and MAF tuning. Should only take a few hours to get things dialed in.

Find a 8.1 vortec tune from the repository and copy the data straight over.

Anything from like a silverado/suburban/avalanche all came with the 8.1 in the early 2000's.

I did the same.The afrs only changed in the cells that I changed to smooth the map which completely makes since. Say the afr was 12.8 in a bunch of cells, but to make the map pretty I have to slightly increas the fueling in four of them, well of course the afr is no longer going to be 12.8 in those four cells so its either 12.8 afr, or pretty map but not both. MAF tune turned out choppy as well but AFRs were spot on. I tuned SD with maf errored out first , then tuned MAF with SD off. LTFT and STFT were disabled during the tuning so they didnt effect anything.I could have been finished months ago if I would have just said screw the smoothing.I mean, I had VE tables tuned in great after about 3 runs but it was the trying to smooth them that kept screwing them up and taking so long. I would have steady 12.8-12.9 afrs, then after I smoothed them out it would jump around to 12.3-13.4 in the cells I tryed to smooth. I kept thinking something was wrong so I kept going on drives.I even borrowed a different wideband at one point thinking my new one wasnt working right.Then I started reading where other people were having the same issues and saying that as long as the afrs were correct,and there werent enormous spikes that that was what really mattered so I put my OCD aside and settled with what I have now. I would love to have it both ways but like I said, now LTFTs are almost all +-1 so I really dont care how pretty the 3D view is....the afrs are good and thats all I care about. The truck drives just as smooth as my stock avalanche, even with the big cam. The KR Im getting from this random commanded AFR change is my only problem now. I just dont understand why changing the throttle doesnt knock it out of that test mode. Youd think GM wouldnt want to cause detonation on purpose.And thanks for the tip BTW. Im definately going to go after those 8.1 injectors if its that easy!