Been having a problem with fuel pressure dropping under acceleration intermittently. Normally runs around 65psi, sometimes at idle or normal driving is only 55-60psi lately. Most of the time it has done this it dropped to 50 and I let of the pedal and it will slowly go back to around 55. Then I just baby it and it will slowly creep back up to 60 or maybe 65. A couple times it has gone below 50 after letting of the pedal and wouldn't go back up, so I actually pulled over and shut the engine off and cycled the key to get it back up. Once this happened while towing up a hill, I could only get to around 35mph really had to baby it and at the top I pulled over and cycled the key and it came right back up. At the time I attributed it to the steep hill, 11k trailer, and the tank only being about 1/4 full.

Since I put the fuel gauge on way before any of this started happening, it has always fluctuated 2-3psi at idle. I always thought it was kind of odd, maybe pointing to combustion gasses entering the injector through a bad seal or something weird like that, but a couple of people have told me that fluctuation is normal. Any ideas there?

I'm thinking there's either a restriction in the fuel pickup or the pump is going bad. This problem happens even when the tank is full, but seems worse on a low tank. I change my fuel filters every 10k mi, I'm at about 9k right now so I guess it could be dirty filters?

Any ideas are appreciated, got lots of towing over the passes coming up as fishing season is just starting and I'm sure we'll be spending as many weekends we can at the beach camping.

 

I had same scenario once and it was the rubber conical seal on the brass poppet valve in the fuel pressure regulator. If you haven't in awhile, I'd consider replacing the fuel pressure regulator with a blue spring kit Ford 3C3Z-9T517-AG.

The black seal circled below had popped out and wouldn't seal enough to build pressure over 55 when prior I had 70 psi. Pulling grade it would get as low as 40 psi so I would let off until it came back up. I took it easy the rest of the time until I was able to take it apart and replace. Since I replaced the regulator parts it's now back up 68-70 psi.

 

+1 on the blue spring upgrade. These trucks are also known to drop fuel pressure below 1/4th of a tank. 45-48psi seems to be the lowest pressure you want to see if you want your injectors to last. over 50psi under load and 60+psi at idle is what you want.

 

Ok thanks, appreciate the picture and the info about your experience. Sounds identical to what's going on with my truck.

I'll take the regulator apart and have a look at it. I still have all the parts from when I did the blue spring update 5 years ago. I bought the whole "kit" but all I replaced was the spring, so I should be able to just swap out all the rest. Let you know how it works out. Thanks.