PCM problem, or something else

[Capt301Ret]

Hi. I have a 98 K2500 with the 5.7. I pull a travel trailer around the country.
Recently the truck started running lean above 3500. First noticed it on a long steady pull up and over a pass. Pedal was floored, in second at around 4K. After the hill, I exited the highway, downhill and it continued to run lean (pooping through exhaust, no power, running rough). Even coming off an idle, truck just wouldn't go. Pulled over, shut it off. Let it sit for a few, then went on my way like normal.
It did this for the rest of the trip, every hill across I-10E in Texas!!
Once I got settled, I starting looking in to things. Here's what I found. Regardless of load, if I went above 3500rpm, it would start to **** all over itself. Both banks LTFT show 9.38 (it rarely will change). STFT stays at 0, and both sensor 1's show 0 volts. If I let off the gas, I would see voltage on both O2 sensors, but 0 STFT. In order to get out of this mode, I have to shut the engine off for a couple of minutes. No amount normal driving will clear it. I've seen lean bank codes, and will have a P0131 and P0151 codes during this time. The EGR code is because I disconnected it to see if it was causing the lean out.

Is this a PCM problem or something putting it in some type of mode?


Thanks!

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

 

[delta_p]

See if the MAF element need a cleaning with MAF cleaner.

 

[Capt301Ret]

See if the MAF element need a cleaning with MAF cleaner.

Thanks, that seems to have fixed it. Wonder why that seemed to throw the PCM for a loop that only resetting would get it out of.

 

[delta_p]

Great!
Probably every time you turn off key, short term zero's, while long term is stored so it just like repeating. If you scan does graphing, always do the MAF, MAP, and i believe you get load on '98, along with the O2 and fuel trims. Can tell you a lot.

 

[delta_p]

Thanks, that seems to have fixed it. Wonder why that seemed to throw the PCM for a loop that only resetting would get it out of.

I thought i would discuss where I was coming from. The dirty MAF makes it easier to maintain the element temperature under high flow so the the MAF tells the computer it is reading good air and fuel is delivered to match it. But really when the throttle is high and the the manifold vac is low there's a lot of air going now but the fuel is low. It would have been nice to see MAF, MAP, load, TPS, O2, and fuel trims at a 100% TPS Wide Open Throttle condition up one of those hills.
I believe it could have been possible to pull over and pull the MAF connector throwing the computer into speed density mode and get fuel neededd, but i am not possitive on these trucks.