Since installing a fuel pressure gauge two days ago, I now have a new obsession. At idle the gauge shows 57-58psi. At WOT it has shown pressure as low as 44psi. Factory spec says it shouldn't go below 45psi. It was due so I replaced the fuel filters this morning. This is what 13 months and 16,000 miles looks like:



Yeah, I know I shouldn't have waited that long. Anyway, the new filters made no difference. For reference the blue spring was installed and HFCM replaced four years and 65,000 miles ago.

Within the last week the truck has developed another issue, or maybe it just became loud enough to notice, and I'm trying to figure out if it's related or not. When the RPMs get close to 3k, I can hear what sounds like a distinct vibration coming from the engine bay. It gets louder with higher RPMs. One way to describe it is that it sounds like a very high frequency belt slap. To my untrained ear I can imagine it might be what a valve seal sounds like going bad. I will try to get a video, but I fear it won't be distinguishable from all the engine and road noise in the cab.

I did a lot of driving today, including pulling a 2-horse trailer 50 miles. Based on my observations the low fuel pressure is only present at lower speeds and high RPMs and the vibration is only present at high RPMs. Is it possible that an injector is being starved of fuel and making an audible vibration that's louder than the base engine noise?

Tomorrow I'm going to see what happens when I rev it up to 3k in park in the driveway. If the vibration sound presents maybe I can get video of it from under the hood.

Any thoughts or insights are welcome and appreciated.

 

Fuel pressure -

You may have something in the tank that is restricting flow, caught against the screen. If you wanted to get nuts, you could run a line from a 5gal can to the intake port of the HFCM and see if the pressure rectified. It would be less work than pulling the tank down.

 

I would need a hose-end/adapter that plugs onto the HFCM that I could then attach to a longer hose and route to a gas can. Any ideas on that? Short of buying an extensive fuel pressure test kit adapter set?

 

I can hunt one down from Dorman on AMZN. The intake is 3/8 while the return to the tank is 5/16.

But you don't need an adaptor, you can just clamp 3/8 fuel line over the nipple. When I moved my HFCM to behind the transfer case I just used hose between the tank and HFCM, no quick connect.

 

 

That's a good point. Thanks for the link anywho, even though it's a Doorman part.

 

You can always install a sump in your tank. That is on my "eventual" to-do list.

https://rudysdiesel.com/series-63-be...-sump-kit.html

 

Other than being able to wait a little longer between refills, what is the advantage of a sump? I could pull the screen off the uptake tube and have essentially the same condition where muck plugging it up is concerned. If that's the problem to begin with.

 

Installing a sump is easier than pulling the intake tube as long as you don't have a ton of diesel in the tank. You can drill a small hole and drain to a few containers, then drill the big hole for the sump. No downside really. Lots of people get scared of hitting it on something, but you would have to be rock crawling to do that.

It is a shorter path to the pump suction, so it should be slightly less suction side pressure loss, but I doubt that it would be enough to make much difference.

Also, if you get bad fuel, it is easier to get rid of w/ a sump. In fact, the sump can help eliminate a stagnant water layer developing over time by drawing off of the bottom. A stagnant water layer will result in biological growth.

Clearly not a "most do" .... I haven't got to it in 218k miles, lol. Just a matter of preference.

 

For the fuel pressure,I’ve seen some of the cheaper (ebay)blue spring kits cause fuel pressure problems.make sure you have a ford one,and installed correctly.

 

Even the Ford kits have not been immune to issues. Now if that’s a materials problem, or an install issue, that’s another question. Mechanically experienced people have had issues, so there may be an undisclosed issue with the install technique that has not been discovered yet.

 

Ok guys, things just got real. Per Jack's suggestion, I put a five-gallon can in the front of the bed and ran 13' of 3/8 fuel line to the HFCM. I drove around my normal test loop, which is roughly 4 miles. It has two long stretches in 50mph zones. I wound it out a few times to see how low I could get the fuel pressure and to listen for the vibration sound. FP went as low as 43psi and the sound was still there. At the top of my street, the FP was 10psi and dropped down to 2 by the time I shut it down in my driveway. I got out and inspected the gas can and it was empty! FIVE GALLONS! There is no spillage in the bed and no leaks under the truck. Yesterday I drove a little over 100 miles and the truck used over half a tank. I told myself it was just the towing but clearly there is another issue. Does that sound like an injector that's stuck open? What's really strange to me is that the truck has been performing perfectly normally, except for that vibration sound. Even with a FP of 2psi the truck idled normally. And the exhaust isn't white, grey, or even visible.

Here's the set-up:

 

That was a longer run then I expected you’d do. I thought you knew the system. It’s all in the tank.

The system is a full volume loop. From the tank, then what’s not used, back to the tank. The fuel to the motor is a bypass leg, downstream of the pressure regulator.

As you use more fuel by the motor, volume is reduced on the return. It should always be pumping the same amount of fuel. Fuel pressure drop should only occur if pumped fuel cannot keep up with demand. Therefore technically pressure at the supply side of the regulator should never drop, if volume is sized for total demand. However, if there is a suction restriction it will go down as volume can’t keep up. Or if the secondary filter is restrictive, or fluid is bypassing the pressure regulator too much. By damaged seals, or the sized air bleed orifice is missing or damaged.

We typically see a small pressure drop at full fuel need, so the system supply is at its limits. Upping the fuel pressure 55 to 65psi does nothing about supply volume.

If the return is blocked, pressure goes up.

 

Thanks for pointing that out. Duh.

What is a reasonable pressure drop at WOT?

Obviously there isn't a restriction in the tank. Where would you look next if at all? HFCM?

Also, the blue spring kit is a Motorcraft, and I followed DieselTechRon's instructional video for the install.

As for the vibration sound, it isn't audible when in park. So I guess it's a transmission thing, or the engine has to be under load for it to manifest.

 

If not the pickup in the tank, I would check if there are any kinks in the line supply line from the HFCM to the secondary filter. I would check in the HFCM if it's an older unit in the water drain chamber. I would check the white air bypass orifice to make sure it's there. Finally, check the regulator to make sure the seal is OK and all the components are in place. They changed the configuration, but I don't have full data on that.

I'd check voltage at the HFCM to make sure it's getting proper voltage, no drop.