Yet another P0171/P0174 thread, Help at my wits end!
Hi Everyone, long time lurker first time poster in need of some serious help.
I'll try and make this brief but as detailed as possible. Ive got an '02 Navigator that Ive owned for about a year, 150k miles and up until 2 days ago was running great!
My wife's car is in the shop so I let her use the Navigator to run around doing some shopping etc, When she returned home she stated that the car was "not driving right", after several questions she said she wasn't paying attention and didn't realize the truck was low on gas till the light came on and then she filled it with 87 octane again without thinking.
I took the truck out and it felt like it had a miss and the check engine light was on, I pulled out my scanner and it was showing codes P0171 and P0174.
I checked for a vacuum leak first thing and found a small one in an elbow and replaced it, no change. I then replaced the fuel filter thinking that perhaps she had picked up some crude from running the tank so low, no change. Took the car in and had a fuel injector cleaning done, thinking maybe some dirt was clogging an injector. The car ran worse. It idles with a lope, part throttle acceleration as well as cruising in the 40-55mph range results in a severe shudder, full throttle acceleration is surprisingly smooth tho..
I then decided to clean the MAf, no change so I replaced the MAf and the PCV valve, again no change.
At this point I'm clueless, the only codes being thrown are a constant P0171 and P0174, I am about 95% positive I have checked and re-checked every vacuum line I have found and still running like crap. I've also read every thread with P0171 or P0174 in this forum and haven't come up with anything that I haven't already checked.
Could it be the fuel pump? fuel pressure regulator? Any easy tests to figure this out?
Any and all help is appreciated at this point, thanks for reading!