Lean/rich condition under cruising
 

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, whom made it run worse on his tune then it did on a stock tune. 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 have a log log and my tune, but not sure how to post it from my phone. I can email if someone is will to take a look! Thanks in advance!

post up a log and tune on hptuners forum. Thin come back and link that thread to this one. I will look it over and try to help.

Hope this works! Thanks!

https://www.hptuners.com/forum/showt...820#post508820

Simple, retune your MAF in OL. Corrections work the same only there is only one line to correct as opposed to an entire table like tuning the VE. Also, sounds silly but watch for small inconsistencies in important sensors like MAP. I had one that was responding sluggish and was giving me fits (similar to what you describe except it happened in OL as well) until i swapped it with a known good one.

Looks like there actually may be some kind of Cat Test going on, and being i dont have rear o2s and there may some interference there. Still trying to figure out that I have everything set properly for that. Supposedy its common on p59 ecms

Make sure all of the proportional fueling tables are stock. Sometimes people mess around with those without knowing what they do, then they get overlooked, because there is no reason to mess with them. Also, I have never heard of unusual issues with a P59 other than the lean cruise and MAF fail quirks of the 2004 GTOs.

Even if the injectors have changed, I should leave the proportional fuel tables stock?

No, but I would put everything back to stock and begin making very small adjustments with regards to the proportional fueling. Who knows what the "tuner" may have changed. It is usually just easier to go back to a stock baseline and adjust than to try to find every little thing someone else may have screwed with.