Lean at rich adaptive limits part throttle

so truck highway drives fine but tail pipe black.
Fuel pressure at idle is 30 with fpr hooked up 40 unhooked
pressure goes from 30 idle and creeps to 38ish when the key is turned off, then holds for ten minutes. I stopped checking at 10 minutes as i feel a pressure issue would show up by then.

I have a filter for it im putting on tomorrow since it has been a while on this one, but i feel if it was a a filter issue it qouldnt run so well under full throttle.

Even part throttle when the check engine light comes on it drives okay. Then just tip in a bit to get vacuum to drop a few inches and the light goes out. Never comes on above 55mph.

Possible it is the hego as it is 150k miles old.

thoughts guys

 

Ok so I got around to doing a koer test today and got a few more codes.

126 map voltage out of range/spec
and
172 hego not switching is or was lean
so im wondering if the map isn't on the fritz. It is original and my vacuum gauge doesn't show any abnormal readings from when this started till now. And im thinking the lean code is because the map is showing low vacuum (hence why the truck runs great at wot and fine at low vacuum highway speeds) but the tps is closed enough at psrt throttle to not call for more fuel so the o2 sensor sees it as too lean.

 

172 and 126 together typically points to a vacuum leak, and that is where I would start. I would also look over the sensor harnesses and check for shorts. If you don't find anything obvious I would pull the computer for inspection. If it looks good, then I would replace the sensors.

 

Ill check the harness today, i checked for vac leaks and havent found anything. Hell at idle it pulls 20 inches and even part throttle cruising is still where it has always run on the gauge i put in the truck.
Really dont want to rhink it's the computer... even though at its age the possibility definitely exists.
Damn thing just runs too well, like other than a very slight smell of extra fuel at round town speeds you wouldn't even know if the cel didnt light up on the dash.

 

I ended up replacing all my vacuum lines, computer, main engine bay harness, O2 sensor extension harness, as well as the O2 sensor and MAP sensor in my journey to cure 172/126 codes. I thought I had it licked more than once. Faulty MAP sensor readings can lead to lean/rich codes. Did you move the HVAC switch to different positions when checking for vacuum leaks? Other thoughts that come to mind (but not necessarily related to your codes) based on what you are saying include injector problems and/or EVAP system leaking.

 

The CanP solenoid was stuck open for sure. That was taken care of then codes reset.
Still had the high map voltage and lean code

checked through stuff this morning and i came to the conclusion of a bad map.

Did the koer warm up cycle ( 2 minutes at 2000 rpm) and tested again.

no map code but now BOTH a lean code and a rich code. Reset eec and will check again after a short drive

 

Well, that new map sensor seemed to fix the lean mixture at part throttle. And even though it never had any issue at wot, it seems to have more power at full acceleration now as well. It must have been slowly going out because i never noticed a big power drop but definitely notice that it is back.