Experience with a P120F?

jared_bortel · May 30, 2008

So i get a truck with an intermittant lack of power, it will happen then goes away when you cycle the key, and eventually will happen again. Obviously truck is going into derate,has consistently thrown P120F exc FRP variation. Due to the limited repeatability of this concern and customer taking truck as he pleases regardless of my opinion of whether it's fixed or not, truck has seen multiple other dealers thanks to the wrecker companies. After a multitude of repairs by myself and other techs elsewhere I am presented with a final attempt lemon law case. Previous repairs, almost all from hotline or FSE's or even a guy from international, iclude but are not limited to; air and fuel filters, frp sensor, pcm, both uvc harnesses, and reprogram. Have personally verified all the basics again today with no avail. At time of concern base fuel psi is 5 psi +/- 0.1psi. Typically at WOT with an FRPDES pid of 24650 and an FRP pid that is between 24500 and 19000. Now I have been instructed to replace the hp fuel pump, the cover gasket, and for shits and giggles a whole main eng harness. I absolutly invite any and all insight and diag advise you all may have becuase S.W.A.G.ging parts at this truck is not only not my intrest but sounds like a great big pain in the ass.

Alex Bruene · May 31, 2008

I worked with an FSE on one that would set the P120F and P0087 codes. It was losing fuel pressure after about 20 minutes of driving. If you shut it off and restarted it, it would be okay for another 20 minutes. It had been at another dealer for 2 months prior to Ford pulling it out of there and sending it our way. Over the course of a week, we replaced the right UVC harness and FRP sensor, to no avail. Then they had me replace all 8 injectors and both fuel rails (they figured there may have been some debris floating around in the rail(s))... still no good. Being a wrecker, it had obviously been welded, so I suggested the PCM may have been at fault, which in the end was the case.

Now that I've got all that out, during the week the FSE was working with me, he had recieved a call from another FSE that was working on a similar case, and it turns out that it appeared to have been caused by an undertorqued (approx. 18 lb/ft) fuel injector causing enough combustion gasses to get in the fuel to screw up the FRP signal.

jared_bortel · June 6, 2008

Thank you for the input. I've been told to put complete eng harness, pump cover gasket and hp fuel pump in it. With verified good base fuel psi I believe that I should be able to rule out a combustion gas blow by issue. I think I'm seeing this pressure drop due to an internal pump failure. Having personally never been into one I dont know the internal design of this pump or frankly even how it works. With an FRP PID that consistently goes apeshit at WOT dropping low and rebuilding psi is this a possibility at this point, anything else I should check?

jared_bortel · June 14, 2008

Just a fast answer. After HP fuel pump and harness replacement the truck ran fine. My best guess was the pump had "blowby" of sorts intermittantly under high load. I have no idea if this is even feasible but it sounds good to me. If anyone has a decent explanation for what may have actually happened please share.

Mekanik · November 22, 2010

I've got a truck with a P120f. I got it to act up once and the FRP would vary 3551psi. I'm not sure what's wrong with it yet, but I put a HP fuel pump in this truck a month ago.

Mekanik · November 30, 2010

Well I drove the truck for a week with a fuel pressure guage hooked up to the shrader valve. I never was able to get the problem to happen agian, so I gave it back to the customer today. We'll see what happens...