I have a 99’ K2500 7.4l with P0172,P0175. Tested fuel pressure leakdown and the gauge went from 55psi to 30 within a couple of minutes. Plugged in scanner, short and long term fuel trims were in the negative through idle, half throttle, and wide open. Did my research, determined likely FPR.

Truck had a bit of a misfire before so decided to do new cap and rotor while I was back there (previous owner did new wires, plugs, and 8 new injectors, cap and rotor were old.)

Got everything back together, fuel pressure leakdown was good. After 15 mins of driving pending codes for P0172/P0175 came back. Since I had the money and the old gal has 175,000 I replaced the MAF, MAP, and TPS sensors. None of the replacements fixed the problem.

After two weeks of going through forum after forum, tinkering and spending all my spare time on this thing, I found a couple threads in which the fuel pump check valve failed and caused this issue.

I spent today dropping the tank, replacing the pump, only to be met with the same pending codes.

This entire time I’ve been skeptical of the O2 sensors as both banks were showing rich and I figured it to be rare that both banks would fail at once. However both downstream sensors are showing 99.2% now leading me to believe these upstream sensors are bad?

At this point I’ve already done the cardinal sin of throwing every sensor and part possible at the damn truck except the O2 sensors, anyone have any experience with this situation? I see in new generation flex fuel vehicles similar problems can exist with the fuel alcohol content being off, but clearly this old girl isn’t sucking down raw ethanol. Any help is appreciated.

 

Got the same issue, any fix for this? Thanks.