Truck Randomly Dies and throws a P120F

CLR95 · August 4, 2014

Been a while since I've posted but I need some extra help. Truck keeps randomly dying. Only code I have is P120F. Truck is an early 08 with 150k. I followed the trouble shooting and everything had checked out.

So when I had the truck running and viewing pids it died. FRP bounced between 7k and 12k psi. FRP Voltage was 1.5 to 1.9. VCV was 0 and PCV was 0. Truck was not running. This lasted approx a minute or 2 and then FRP went back to 50 psi and kept falling the longer it sat. The code did not reset.

My question is do I have a FRP issue or do I have a HPFP harness starting to short out? I don't want to throw parts at it and hope it works. Didn't know if anyone has seen anything similar.

It has only died going down the road twice. It dies at idle and while backing up more often. Makes me thinks its the pump harness but haven't seen enough of these to be confident about that decision.

Thanks for your help in advance.

BigWalt · August 4, 2014

does sound like air bubbles in fuel system.

did you check for air bubbles?

CLR95 · August 4, 2014

No I have not. Air bubbles on the supply or return side? I did notice an air sound coming from the fuel tank KOEO. Lift pump has good supply pressure.

BigWalt · August 4, 2014

check for air bubble at one of fuel cooler line.There is tool for checking air bubbles, go look at shop manual.( I am home now, dinner is coming up, don't have the time to give you tool number, maybe later )

Brad Clayton · August 5, 2014

My question is do I have a FRP issue or do I have a HPFP harness starting to short out? I don't want to throw parts at it and hope it works. Didn't know if anyone has seen anything similar.

A quick and easy check for the FRP connector is to remove the oil fill/crankcase depression regulator off the right valve cover, then you can look down in there and see if the connector is coming loose and making a shitty contact or not. I always zip tie the connector if I have the valve cover off. As far as a pump harness rubbing, it seems fuse 74 would have blown by now. You might could drop the fuse rating down a bit and see if blows.