Wierd lean/rich condition on freeway

[Miked.]

Hey guys, I have kind of an odd situation hoping you can point me in the right direction. I have a 2006 GMC Sierra that I recently swapped an lq9 into, 228/234 cam, CNC/milled 799s, ls2 TB, ls3 injectors and tbss intake.

I brought it too a tuner, who did his best to get it dialed in, but it wasnt quite right. Anyway, I decided to roll my sleeves up and try to get it running better on my own. Fast forward a few weeks and the truck runs "well" but not perfect.

My current issue im trying to iron out is a condition where as I enter the freeway, fully warmed up, CL etc, as I begin to come to crusing speed the truck will lean out, o2s will go flat to like 60mv (roughly), and it sit between 16.5-17.0afr, it will seem down on power a bit. This will continue maybe 3/4 minutes of driving. Then I'll feel a change in power, it will pick up in power, then it will be 12.9-13.2 afr, this again will run for 3/4 minutes.

Eventually, the truck begins to "settle" and I'll have a normal 14.6 afr, o2s go back to cycling, and all is well. Now I know it has to do something with the MAF, as SD mode it runs "perfect", gets way better mpg, and afr doesn't fluctuate on the freeway at all, and response as it should.

Again I'm new to tuning and have done my best to research but I haven't come up with much so far? Any suggestions?

I hope this works, first time I've tried to upload file.
Log and file>>>

Freeway leanrich.hplracetruck-Justin ve maf pe.hpt

[5FDP]

Are you running long tube headers without rear o2 sensors?

[Miked.]

Are you running long tube headers without rear o2 sensors?

Yes I am? But there set to no error reported?

[5FDP]

That's likely where your problem is, you can't turn off the CAT test that happens when you remove the rear o2 sensors from the harness. Your current tune file also has the several of the rear o2 sensor codes still set to second error and the P0420 and P0430 are still active.

I've dealt with this problem a few times before on P59 computers. I always plug the rear o2 sensor back in, zip tie them to the frame and set all rear o2 sensor codes including cat codes to no error reported.

[GHuggins]

Listen to the man ^^^ It sounds exactly like cat and O2 test - that's how the ecm test for functionality of the cat and O2's - newer gens do the same thing, but over and over and more often such as initial fire up and highway speed cruise scenarios - it'll swing fueling really lean then back rich for mv confirmations...

[Miked.]

That's likely where your problem is, you can't turn off the CAT test that happens when you remove the rear o2 sensors from the harness. Your current tune file also has the several of the rear o2 sensor codes still set to second error and the P0420 and P0430 are still active.

I've dealt with this problem a few times before on P59 computers. I always plug the rear o2 sensor back in, zip tie them to the frame and set all rear o2 sensor codes including cat codes to no error reported.

I know this would be a lot to ask, but anyway to find or post a list of all codes that need to be set to no error?

But let me see if I can get this straight.

Install rear o2s, and ziptie them out of the way, make sure to set all codes for rear o2 to no error reported, including the 420/430 codes. Now is there a CAT test code, or box that needs to be set to enable or disable at that point? Only thing i see is CAT overtemp

[5FDP]

P0137, 0138, 0140, 0141, 0157, 0158, 0160, 0161. Then P0420 and P0430.

Correct, plug them in and zip tie them out of the way. There in no CAT test that you can disable, that's why I said you can't disable it and it normally only trips this test if the sensors are removed from the harness.

[Miked.]

P0137, 0138, 0140, 0141, 0157, 0158, 0160, 0161. Then P0420 and P0430.

Correct, plug them in and zip tie them out of the way. There in no CAT test that you can disable, that's why I said you can't disable it and it normally only trips this test if the sensors are removed from the harness.

Awesome, thanks so much for the info. I'll check back and let you guys know if that was the fix!

[lsa_truck]

I think a true trac would fix your issue

[Miked.]

Well, zip tied up the o2s, turned anything that say o2 sensor 2 to no error reported, and re flashed. Still seems to be acting the same. Do I have to unclick ses enabled also?

[Miked.]

Well, zip tied up the o2s, turned anything that say o2 sensor 2 to no error reported, and re flashed. Still seems to be acting the same. Do I have to unclick ses enabled also?

Actually i take this back kinda, seems it going lean has stopped, so i just see short runs of rich (12.9-13.2ish) for a few minutes after i start the truck/cycle the key.

And just for shits, does SES Enabled boxes even change anything, whether is clicked or unlicked, after you set the code to 3?

[Miked.]

Just bumping this post in hopes for a little more help. Still getting periods of running really rich, during this time the pcm commands 13.6. Would this still be the cat test, or is this something else possibly

[5FDP]

So now it only does it once or twice per key cycle and stops?

Or does it continue to do this while going down the road no matter how long you are driving?

I'm kind of out of idea's for making changes. The codes and the sensor thing is what has done it for me. If you are able to tune the vehicle in open loop for both VE and MAF using an AFR/Lambda error you should be doing just fine, then re-enable closed loop once you are done. Then you may have to deal with the random rich condition if it only happens a few times.