Thanks for looking. Bear with me, lots of info here. 2004 F150 FX4 extended cab 5.4 with 144,000 miles.

About two weeks ago the truck wouldn't start in the driveway. I check a few simple things, then checked the fuel pump driver module to find it cracked open. I bought a replacement at Advance Auto, installed it, and the truck started right up. I took the opportunity to change the fuel filter at the same time because it was due.

I put about 20 miles on the truck over several days and it ran smooth and fantastic with no issues. About a week ago I was coming up the hill towards our house and it seemed to lose power, started spitting and sputtering and actually stalled. It started right back up and I was able to get it into the driveway. It was late so I left it alone that night.

The next day it started right up and seemed to run smooth. I decided to double check the connection at the FPDM to make sure it was on tight - it was...no issues. I had some errands to run so I headed out with it. As soon as I was headed down the hill again it started sputtering again. I pulled out onto the main road and it died right after, but started right up again. I made it about a quarter of a mile before it stalled again. I started it and shut it off several times and it began running well enough to drive another 1/4 mile and pull into the Advance Auto. I intended to stop there anyway and check on the warranty of the FPDM I had bought. When I left Advance the truck started right up and ran smooth. I did my errands around town and it ran perfectly...no issues whatsoever.

I stopped into a friend's shop and we checked the fuel pressure at idle on his Snap-On diagnostic computer - it read between 30 and 40, so normal I believe. No trouble codes in the system. I shut it off and restarted it several times to TRY and get it to run like crap...but it wouldn't. It did however finally through a code - P0175 System Too Rich (Bank 2).

I left his shop and started driving home with it running perfectly. As soon as I started up the hill towards the house it started spitting and sputtering and stalling again. I got it into the driveway, and since then it will start right up and immediately start to spit and sputter.

Again, I double checked the wiring on the FPDM. I made sure the connections are making contact, and I cleaned up the ground wire. It still ran like crap, so I removed the FPDM and had Advance swap it out for a new one. Same problems.

I scanned it again and it now has both codes - P0175 and P0172 - System too rich in both banks.

I unplugged the pressure sensor on the fuel rail (thinking if that was failing the PCM would substitute in a "safe" value to make the truck run) and nothing changed.

So...

I can hear the fuel pump prime when I turn the key and it does start right up...could the fuel pump still be bad? I hate to just throw a fuel pump at it unless I'm fairly certain it's bad.

Is there anything else that tells the fuel pump what pressure to put out on a returnless fuel system like this? I'm going to have to my friend stop by after work and read the pressure at idle (hopefully it's still running rough).

It's odd that the problem seems to show up going up and down hills...that does lead me to believe it could be the pump. It has just under a 1/4 tank of gas (and I'm certain the gauge is right). I hesitate to put more gas in in case I have to drop the tank for a fuel pump change.


Any advice or help is appreciated! Thank you!

 

One would think that the fuel pump is fine if it's throwing rich codes.

 

One would think, I agree.

I have read that the rich code just means that the ECM is calling for too much fuel..can anyone confirm?

 

https://repairpal.com/obd-ii-code-p0172-and-p0175

 

Great info, thank you!

 

Based on what I read about MAFs in that article I tried unplugging it so it would default to a safe value, started the truck, and it ran great!

An MAF is always one of those things I feel like people throw at cars to fix them and they are rarely ever the problem. This is the first one I've ever had go bad in any vehicle.

 

Are you using an oiled type air filter?

 

No I'm not.

 

Well, I threw an MAF at it and the problem is still there. Idles great when the MAF isn't plugged in though.

Any ideas, anyone? What else could cause that? At least it rules out the fuel pump.

 

Update:

I disconnected the battery and left the headlight switch on for about 15 minutes to drain any power from the PCM. I started it back up and let the PCM relearn the idle...and it's running pretty good. A slight hesitation everything now and then, but nothing like it was. Much much better.

The CELs have returned though...rich condition on both banks still. I'm going to give the throttle body a good cleaning...that can't hurt. Anyone have any other ideas?

It's due for a spark plug change so I'm going to do those again...maybe they got hosed when it was running like crap?

I'm going down the list of possible causes that was in the document linked above...just hoping someone has an idea to chime in with.

 

Running rich will plug up the cats sooner or later.

 

Sounds like leaking fuel injectors.

 

Lift the fuel rail with the injectors. Place a piece of paper under the injectors, turn the key on. If any are leaking you will see it.

They may also be dirty, throw a couple bottles of Techron in the gas.

Watch this video before cleaning the throttle body!

 

I will try that, thank you!