[vitaminjoe]

Hello all,

Been quite a while since I posted anything here. My truck (details in signature) has been having a weird fuel pressure issue for the last 6 - 8 months. I've searched around and can't find anyone with similar symptoms.

After a cold soak (more than 24 hours after driving) my truck fires up just fine and shows almost exactly 60 PSI fuel pressure at idle. I let it run for about 15 minutes and pressure will still be in the 58.5 - 60 PSI range after oil temp >100F.

Driving at city speeds, the pressure hovers around 55-60.

However, after about 45 min at highway speeds something weird happens. Pressure slowly begins to drop. I lose about 1PSI every 5-10 min. After nearly an hour pressure bottoms out around 45 PSI. If I do a WOT run when it's this low, it will drop even lower (which I know is bad news).

If I pull over and and park, pressure will usually come back up to around 47-48PSI, but never go back up to the 60 PSI range when the engine was cold. I can shut down the engine, wait 5 minutes and re-start and the pressure is still in the 45-47 PSI range.

This would all be well and good if this problem happened every time... but, if I leave the truck for maybe 3 - 4 hours and then drive again, I have absolutely no problem. I can drive back home on the exact same route that takes the same amount of time and pressure will remain within 55 PSI - 60 PSI the whole way.

All other vitals of the truck are good. Fuel filters were changed about 4000 miles ago. There is no sign of a leak in the fuel system anywhere. Exhaust seems normal with no sign of fuel at the tailpipe.

I haven't done anything yet to fix it... wanted to get some ideas from the community here first. I do have an adjustable fuel pressure regulator on my bench ready to go in if needed. I'm hesitant to install it as my problem isn't consistent. This low fuel pressure issue only seems to happen intermittently... but when it does, the problem stays there until the truck has cooled for a while.

Maybe a bad O-ring internally somewhere? No sign of fuel in the oil (that I know of)... and my MPG hasn't changed much... Maybe the regulator is getting stuck?

Any ideas would be welcome. Thanks!

 

[bismic]

Sounds more like a bad fuel pump to me.

Very good thing that you monitor fuel pressure!

 

[TooManyToys]

Considering how pricing of the HFCM and fuel pumps are going, I’d probably pull the HFCM manifold cover, check out all the cavities and if the ports are clear.

Are there any changes to the fuel tank, such as adding a sump?

 

[bismic]

Seems like fouling in the HFCM wouldn't follow the described pattern quite so repetitively, but inspection inside the manifold is a good (and free) recommendation.

Maybe I am just spoiled with good fuel availability, but I have a hard time understanding how heavy fouling can happen without first seeing it in the water drain or the filter change out. Just lucky I guess.

 

[TooManyToys]

Agreed, it's not what I would expect either, but I think it's worth checking. It would take an extraordinary circumstance for something like a fuel additive seal to make it to the ports and clog, but .... I've had it happen on a tractor. From the tank, though the tube and made it to the fuel strainer.

If I ever get my voice back, I've got a video .....

 

[bismic]

The dealership techs sure hate fuel additives. So many seals found in tanks, lol.

 

[vitaminjoe]

Hey guys,

Thanks for the quick response. I don't think it's a fuel additive seal... although I know there are some screens/filters inside the tank that could be an issue. I really doubt it though, considering that the problem is intermittent. Diesel Tech Ron had a video about the internal screens/filters:

• FORD POWERSTROKE DIESEL LACKS POWER ON ACCEL DUE TO FUEL RESTRICTION

It's very possible the HFCM is to blame... as far as I know it's still the original factory-install pump. I'll pull it out and check the manifolds to see if there's anything going on in there.

I'm pretty sure the pump I have includes the fuel heater, which I don't think is included in the PFB-101 pumps anymore. A fuel heater relay that sticks on wouldn't be part of this issue?

 

[bismic]

The fuel heater electrical system would not cause any running issues.

 

[bismic]

The Parker-Hannifin (Racor) pump number is: PFP58054

#46-047 Racor PFP58054 FUEL PUMP ASSEMBLY

Replacement pump for the factory chassis mounted fuel filter/water separator pump assembly.

www.dieselorings.com

2003-2007 FORD 6.0L POWERSTROKE / RACOR PFP58054 PARFIT REPLACEMENT PUMP

OEM & Aftermarket OE Replacement Parts. We also stock a full line of Diesel & Off-Road Aftermarket Performance parts. ARP Bolts OEM Genuine Ford Edge Products SCT aFe Power Alliant Power Bosch Mahle Victor Reinz Bostech PPE Diesel Rx Air Dog Fass Fuel Systems AC Delco Mopar Husky Liner...

swagperformanceparts.com

 

[TooManyToys]

The fuel heater electrical system would not cause any running issues.

Yes, it can, Mark. If the heating chamber fills up with enough crud to block the flow.

 

[bismic]

Yes, it can, Mark. If the heating chamber fills up with enough crud to block the flow.

I specified the electrical system, since he specifically asked about the relay.

Compartments clogging are something else.

 

[vitaminjoe]

Thanks for the parts links and info about the fuel heater. I'll get the pump off the truck and see what lurks inside... I'll update the post once I get a look.

 

[TooManyToys]

I read that as though the fuel heater electrical system still working rather than disabled as per the TSB.

 

[bismic]

Whatever - he asked about a sticking relay ...................... I replied. Nothing more.

 

[TooManyToys]

But a fuel heater relay that sticks on would be an issue as it would provide power to the thermostat 24/7, so anytime the fuel goes under 50ºƒ the heater would cook the fuel and cause more debris, engine running or not. The feed to the relay is hot all the time. So it could contribute to the issue of clogging. If that is the issue.

 

[bismic]

Wouldn't the heater bring the temperature up above 50 and the shut off, therefore 24/7 isn't realistic as it pertains to cooking the fuel (just askin' anyway)? Not to mention do a number on batteries until the heating element burnt out.

 

[TooManyToys]

It draws 4.5 amps, despite the 30a fuse, so depending on the time it's on..... The thermostat range is 50ºƒ on to 80ºƒ off. I wasn't saying the heater was on 24/7; I was saying it can engage anytime the fuel in the heating chamber drops below 50º, 24/7, without the engine running. Depending on the ambient temps and the HFCM cooling rate, maybe once per night, twice, or whatever. Without fuel flowing through the HFCM, it's a small pocket, so concentrated there, but with a decent mass to draw it back down.

It can be a noticeable overnight battery draw down, but many variables exist. A weekend, I could see that. But the question was singular, would a stuck relay contribute to a blockage from debris?

 

[bismic]

I still say no in practicality, lol, especially in singularity (and also in the OP's case where the truck does perfectly fine after it has been allowed to sit for 3-4 hours).

 

[Duct_tape123]

Check for debris in the tank. Try an alternate fuel source plumbed into the HFCM if able. Remember to also route the return line to the alternate source or you will run out quickly. See here for an issue I had

 

[vitaminjoe]

Hey guys,

Thanks for the analysis of the heater idea... I have no parasitic draw on the truck, as it can sit in the driveway for a couple weeks and still fire up without issue. All good on that front. I haven't pulled the HFCM yet. Too cold out still to justify laying on the ice/snow under the truck... I'll wait until it warms up a bit before digging into it.

It's definitely an intermittent issue. I've started to log my fuel pressure readings at cold-startup and at hot idle after at least an hour drive at highway speeds. Last two highway drive cycles have been absolutely perfect.

2023-03-13: Ambient 16.4ºƒ - Fuel Level: 60% - Run Time: 65 min - Distance: 56 miles - BatV: 14.1V - Cold Start Fuel Pressure: 61.4 PSI - Hot Fuel Pressure: 58.4 PSI - WOT: 53 PSI
2023-03-17: Ambient 25.2ºƒ - Fuel Level: 52% - Run Time: 62 min - Distance: 53 miles - BatV: 14.0V - Cold Start Fuel Pressure: 60.4 PSI - Hot Fuel Pressure: 57.8 PSI - WOT: 53 PSI

I've had a few shorter drives in between, but this issue has never shown up on short drives... only on 45 min+ drives at highway speeds.

The only other detail I've considered is that the last time this strange fuel pressure reared its head, I had started with a full tank of fuel. I'll be watching extra close to see if that has any bearing on the problem.

I really hope it's not a broken pickup foot and debris in the tank as @Duct_tape123 mentioned... dropping the tank will be the only way to fix it. I've got an after-market 5th wheel rail mount in my bed, and removing it is probably harder than dropping the tank... especially given the amount of rust under there!

I'll keep tracking the data and will update this post as information becomes available...