Power enrichment

Hi Paul, my name is michael and I’ve been needing a life line for a power enrichment problem on an 2002 GMC Sierra 6.0l. Symptoms are the vehicle seems to feel really numb on a launch. So watching scan tool data, upstream O2 sensors are NOT going full rich during a first gear wind out. Short term trims look great at idle. With a total trim of about 3 on B1 and 7 on B2.
One anomaly I do see with the vehicle fully warm. The down stream O2 sensors are indicating lean at about .100mv. I would expect to see .700mv. I’m hitting the number on the MAF. Have not verified fuel pressure yet but fuel trims are not indicating a fuel delivery problem. No DTCs. Can you help?

Hey Michael, welcome!

Is there any way you could post the data from one of your first gear test drives? For comparison purposes.

So watching scan tool data, upstream O2 sensors are NOT going full rich during a first gear wind out.

Strange as it may sound, but there's many GM's out there that DON'T go into a typical 'power enrichment' mode at WOT. They'll stay in closed loop for the whole run, short term fuel trims and all. :silly: Fortunately, you can still pick up on driveability issues by watching the short terms during the same WOT run. Fuel delivery issues will result in high trims, just like normal.

The down stream O2 sensors are indicating lean at about .100mv. I would expect to see .700mv.

I would, too. Do they ever behave correctly? Any exhaust leaks?

I’m hitting the number on the MAF.

I figure you're talking about MAF Hz, right? 9000 or more? That'd tend to rule out a volumetric efficiency or airflow measurement issue.

For reference, here's some data from a Silverado with the same 6.0L.

www.scanshare.io/share/xnY9cwo1qUq_lmsxOfHQvg

You may well have a fuel le delivery problem. The effect of restriction is greatest under high demand conditions. So at idle everything can be fine but boy, going up the hill....
Check fuel pressure & volume and go from there.

Don't worry to much about the back O2 sensor yet. Its low reading might be the way it's designed. You may want to do enrichment /enleanment test to verify the front O2 sensor responds correctly.

ill try to upload from my solus pro if I can. I will also do the fuel volume and psi test. the vehicle has had many parts thrown at it before I got it. mass air flow sensor, fuel pump fuel filter, etc. customer has told me that he frequently has put fuel treatment in the tank and from the sounds of it excessively so. I will get back when I find out more.