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Low Fuel Pressure at WOT

5K views 39 replies 7 participants last post by  Hydro 
#1 ·
Yes. I know. Another low fuel pressure thread. 🤷‍♂️

Pertinent truck specs:
2005 F250, Colt stage 1 cam, Atlas 40, blue spring upgrade (not OEM, but only ~ 5000 miles old). Stock turbo and stock injectors.
Cleaned HFCM and installed new filters <1000 miles ago.

Recently I noticed my fuel pressure dropping when I really feed 'er the onions. Idle pressure holds about 58-60, cruising is around 55, drops to 48-50 going up a hill. That seems low, but not alarming, until I decide to have some fun and put my foot into it, and then it drops into the 30s. I think I even saw it dip below 30 at one point, but I immediately let off, because, you know, I like my injectors the way they are. Pressure measured with a gauge coming straight off the HFCM shows 70psi.
I'm leaning toward probably the pump, but I wanted to be sure, so I've done some bench testing and in-truck testing. First bench test was to see if the HFCM was sucking air, second was testing max pressure, and the third was back in the truck pulling from the tank, checking for air as well. You can see it better in these videos I took.
The only thing I didn't do in these videos was to check for air with the module installed normally, with the return lines hooked up. I can do that too, if anybody thinks it's necessary. Your input is appreciated. I thought about replacing the whole HFCM, but after my bench tests, it doesn't look to be bad.


 
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#2 ·
Font Circle Brand Logo Darkness


Since you have a 2005, does the HFCM have the fuel heater (early 2005)? If so, was the cover ever removed and the area cleaned?
 
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#3 ·
Since you have a 2005, does the HFCM have the fuel heater (early 2005)? If so, was the cover ever removed and the area cleaned?
Wow, thanks for the quick reply!
No, it does not have the fuel heater. And yes, it has been thoroughly cleaned, about 800 miles ago, following your instructional video. Thanks for that one, BTW!
 
#4 ·
Nothing special about your pressure results. The original pump wasn't made for anything above basic driving. The fuel filters need changing if the pressure drops more than what you expected. With a wider PW you could expect <20psi for extended full power runs; that is why regulated returns with larger fuel pumps are recommended with power upgrades.
 
#5 ·
Stock, is a regulated return. LOL.

BE, I should have waited for the videos to be viewable. Good work.

When you are deadheading one of these, it should go up to ~100psi. That is where the internal blow-off valve is set within the removable pump. When I had a blockage, it got that high and screamed like a pig. So that's one oddity.

The reason I asked about the fuel heater is I have a video in waiting for when I can do the narrative. My voice has been screwed since July when I got Covid due to fungal nasal issues. But the video is the forensics on two HFCMs that members of FTE sent me, which failed to pump. Both had running motors. The spoiler of the video is one was blocked in the heating chamber from all the fuel debris off the heater. The other was blocked by debris in the HFCM nipples. The truck probably had a bad case of organics, the primary filter failed, and debris was everywhere. Including on the face of the 100psi blow-off valve. This then may have allowed the valve to leak all the time to some degree, and you could never get the full 60-65psi, or if it were a small leak, you would get below the normal 52-55psi the majority of us see when we go PTF.

When I used my HFCM to pump out my tank for removal and looped the return, it showed air/foam for longer than I expected. I don't know how long you pumped like that with the loop to check for air. Unfortunately, I did not video much of doing it - I didn't think there was any relevancy at the time.

Curious what is going on there.
 
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#6 ·
Sounds intriguing. I look forward to seeing that video, though I hope I can get my rig fixed before that...

I ran the pump like that for at least 2, maybe 3 full key cycles (pump runs for 20 seconds, right?) before I took the video. The first cycle was just barely enough to get prime the module and get a bit of fuel out the outlet. The majority of the air cleared up pretty quickly after that.

So, since I'm only getting 70psi, would you say my pump is probably bad? Or perhaps the blow-off valve? I'm curious if maybe the pump is weak, and while it builds moderately decent pressure, it's not able to flow enough to keep up with the demand of a WOT run. I wouldn't rule out the possibility of it sucking air in somewhere between the tank and the HFCM, but judging by the fairly small amount of air coming through, I doubt it would be enough to cause the problems I'm having. Am I making any sense here at all? :rolleyes:

Just for the record, the truck was running just fine, the only symptom was the low pressure on the gauge. Also, the tank is right at half full (minus however much I've pumped out into the can, lol)
 
#7 ·
It's late -if this makes sense.

For you to have more than the normal 10psi drop from idle to WOT with this system says there is a volume issue. So it's either delivery to the HFCM, or an output issue. The regulated output can be less due to leaks around the pressure regulator seal, the air bleed orifice at the top of the secondary filter, the blow-off valve leaking, or electric motor deficiency.

Voltage should be near battery voltage (whatever that is) when the key is on. Otherwise, there is resistance in the circuit cause low power. While you are doing your key-on checks, unbolt the alternator lead off the passenger battery positive. That also feeds the GPCM, which will pull down the voltage when you check. The voltage should be checked at the pump connector while the motor runs.

The only way we mortals can check the tank supply, if everything else is good, is by using a remote tank/can as the tank, with both supply and return into the container if you going for a drive. The HFCM will pump the 5g container (or whatever) into the tank if the return still goes to the tank. If it's still more than a ~10psi drop under WOT, then we are at the fuel pump. And those are replaceable only. I just destroyed two good (one relatively good) fuel pumps doing the full forensics, unfortunately, or I'd send one to you.

Just for a data point, when I pumped at no pressure, it required 2.7a, and at 65psi 5.3a, off a fully charged Group 65 battery.
 
#8 ·
Check the nipples on the HFCM for debris blockage
remove the side cover
also inside the filter cavity where the fuel enters

then there is the internal pump screen -- no way to check that one
if the HFCM inlet is clean - checked visually
then a fuel can and hose on the suction
and see how much flow the pump will output

@TooManyToys may have some pump flow information
 
#10 ·
From my contact with Parker:

Good morning. I am the pump product manager at Parker Racor and spent many years working on the 6.0L Ford Fuel System.
The Ford 6.0L fuel system is set in the mid 50 PSI range I believe. The pump when running at alternator voltage will produce around 110 LPH (29 GPH) at 60 PSI outlet restriction.
So when the pump is installed on the vehicle the flow could be as high 32-35 GPH when the filter on the frame rail is clean. As the frame rail filter starts to choke the flow may drop 2-3 GPH.
Please let me know if you have any specific other specific questions about this pump.
Thank you
xxxxxx
 
#12 ·
If I remember right, it was this one from XDP. I bought it quite a while ago, but only installed it last year (not brilliant, I know...).
I'm slowly learning my lesson on which parts are ok to go aftermarket, and which ones to go OEM.

I'm waiting to hear back from my brother on a price for a Ford kit. Nice to have a brother who works for a Ford dealer!

I'm thinking about pulling the regulator back off and checking the seals and such. Not much I can tell on the spring itself, but this doesn't seem to be a pressure issue directly, rather a flow issue that manifests itself as a pressure drop under load. My only hesitation about condemning the regulator is that I know the pump is only outputting 70psi, both on the bench and in the truck (I tested the output pressure this morning with the inlet hooked back up to the tank).

Allow me to think out loud for a minute. The blue spring is supposed to bring it up to the 60psi range, right? So if my pump pressure is 10psi higher than that, but my regulated pressure is right around 60, then that should tell me that the regulator is doing its job properly. The fact that the pump is only at 70 makes me think the pump is weak. If it's not able to make 100psi, will it be able to keep up with the flow demand at WOT? My gut is telling me I have a weak pump, but I'd sure like to verify that before I spend the money on it. I don't mind spending money, but I hate wasting it.

From my contact with Parker:

Good morning. I am the pump product manager at Parker Racor and spent many years working on the 6.0L Ford Fuel System.
The Ford 6.0L fuel system is set in the mid 50 PSI range I believe. The pump when running at alternator voltage will produce around 110 LPH (29 GPH) at 60 PSI outlet restriction.
So when the pump is installed on the vehicle the flow could be as high 32-35 GPH when the filter on the frame rail is clean. As the frame rail filter starts to choke the flow may drop 2-3 GPH.
Please let me know if you have any specific other specific questions about this pump.
Thank you
xxxxxx
Thanks for these specs. Maybe I'll try to rig up a jug to the return line from the secondary filter and time it to get a rough idea what the flow rate is.
 
#13 ·
Thanks for posting that, Mark.

The regulator at the secondary filter has nothing to do when you deadhead the system. Over the 55 to 65 psi range of the regulator at the engine, it will open more when deadheaded to try to get down to the stated pressure. Then the blow-off 100 psi regulator in the pump will be the dominant control.

Even if the flow input were restricted, it would only take seconds longer for the pump to reach 100psi when deadheaded; there is no volume or flow; it's all pressure generation. It should be at 100psi. When you are in a bypassing loop, flow or volume matters.

In-pump relief valve.

Hand Finger Household hardware Watchmaker Automotive tire


Debris on the valve that can keep it open, causing a lower pressure when at injector full demand.

Finger Clock Household hardware Nickel Jewellery


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So I think either your pressure gauge is off, you have resistance in the circuit feeding the pump (voltage / current low), or the electric motor is damaged. Unless someone else has another view. Being an R&D guy, I always expect to be 80% wrong.
 
#14 ·
Has your fuel pressure always been this way or did it just start? Or...did you just start monitoring fuel pressure and that's what brought it to your attention?

Reason being, I had a similar issue on mine last year ~100 miles after getting fuel from a truck stop in Southern Oregon. I monitor my fuel pressure religiously and noticed it was dropping to low 50's under light to moderate throttle and was dropping into the mid 40's WOT! My truck had NEVER gone below ~52-53 psi at ANY kind of throttle input, so I took note. Ended up changing both fuel filters and everything returned to normal.

Not saying this is your issue, but it's worth the $50 for a set of fuel filters before you change out a $350 HFCM.

-jokester
 
#16 ·
Has your fuel pressure always been this way or did it just start? Or...did you just start monitoring fuel pressure and that's what brought it to your attention?
-jokester
A little of both. I did just start monitoring fuel pressure a few months ago. (Another one of those "bought the parts, never installed them" situations.) However, I'm pretty sure it wasn't doing this when I first got the gauge. And it may be my paranoia, but it seems to have gotten a little worse since I first noticed it.

Bad tanks of fuel, for color commentary.
Woah, that's disgusting. I just pulled mine apart for grins and giggles, and it's not at all dirty. Maybe a small amount of debris, but some of that may have fallen in as I was taking it apart. Here's a few pics.
Automotive tire Rim Gas Automotive wheel system Auto part
Tool Tap Gas Cylinder Metalworking hand tool
Wood Gas Bumper Automotive exterior Automotive tire
Automotive lighting Bumper Electrical wiring Gas Motor vehicle


So, I've pretty much decided to go ahead and throw a pump in it. I suppose I can't be 100% sure that's it, but every test so far has pointed me in that direction. Next question: you mentioned in your HFCM video that Racor sells their HFCM to Carter and Napa. I see on RockAuto I can get a Carter pump (just the pump) for $61.89. Does the same go for the pumps, or do I need to try to find a Racor pump? Looks like they're up to around $200 now.
 
#15 ·
I think he has been through all that.

Bad tanks of fuel, for color commentary.

Circle Auto part Gas Metal Serveware
Wheel Automotive tire Automotive lighting Motor vehicle Alloy wheel


To the right of the o-ring should be clean fuel. Failed primary filter.

Cylinder Gas Wood Auto part Metal
 
#17 ·
Wow the OEM fuel pumps are close to $300. It wasn't that long ago that they were $120.

Racor: PFP58054

You can get it at DieselFiltersOnLine for about $290 and free shipping.

$280 at the Racorstore and who knows how much for shipping.

Jack has posted that the aftermarket brands are probably re-labeled racor, but hopefully he jumps in for himself on this topic!


 
#20 ·
Holy crap! For JUST the pump! If I was paying that, i'd put in a whole new HFCM for $300, but that's JMHO...

-jokester
Ouch! Yeah, I agree, If I'm going to spend that, I'll just get the whole HFCM. I think (would need to double check) that my brother can get one for about $220. Again, good to have friends in high (or just strategic) places.
 
#18 ·
Holy crap! For JUST the pump! If I was paying that, i'd put in a whole new HFCM for $300, but that's JMHO...

-jokester
 
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#19 ·
I couldn't believe it either. Glad I have already made that purchase! 2023 may be a year of stocking up on critical spares to beat inflation or the targeted attack on parts availability for non-electric transportation ........................
 
#22 ·
Riff Raff sells the entire HFCM for about $310 - not bad considering!


Lowest price I found on the pump - $242 + shipping.

 
#23 · (Edited)
DAMN!!!!!!

I bought mine back in 2016 to have on the shelf, and I bought a complete HFCM a few years back.

I felt bad a little while ago when I destroyed the two pumps for the video. Now I really wish I never did.

My pump order from Diesel Filters.

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The full HFCM (Carter)

Rectangle Font Parallel Screenshot Pattern

Font Circle Art Sky Logo



This is a complicated pump, so some of the aftermarket companies that would private label from Racor may not have changed their pricing as yet. I may order one to see if it is the same part, as best I can tell.
 
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#24 ·
Back then, I bought 2 HFCMs to compare, one Carter (NAPA) and a Delphi. Both were actual Racors. Carter is part of Federal-Mogul.

Both had this situation; Racor tried to obliterate the Ford logo on the bracket rather than stamping a new bracket.

And part numbers that are on the cap of a Racor pump.

Font Rectangle Paper Document Paper product
Font Material property Drink Gas Cylinder
Bumper Tints and shades Gadget Rim Automotive exterior
Helmet Automotive wheel system Personal protective equipment Auto part Automotive tire


I sent one of the HFCMs back to RockAuto. I also bought several years of FoMoCo main battery cables when they were in the $80 range to take measurements. I sent them all back; last I saw, they were selling for a few hundred at dealers.

It's looking like parts do better than some stocks.
 
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#25 ·
Yeah, just think of your ROI if you have kept those parts and still had them 🤣 100%+ on some!!

-jokester
 
#26 · (Edited)
I've got '66 GT-350 parts like that. But the reality is you can still do better with stocks.

Back to the subject. I just ordered an Airtex pump from RockAuto, so I will let everyone know if that is a Racor when I get it. Airtex is an OE water pump manufacturer, but I know they private label parts for their aftermarket sales.

The Airtex pumps were not, nor ever have been, in the cheap China parts cost range. Hopefully, they haven't caught on yet. Used a RockAuto discount code. RockAuto lets you use their cheap shipping if you send it back.

Rectangle Font Parallel Screenshot Number
 
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#27 ·
$143 for the chiina version on amazon
found a Carter (or at least the dust caps are the correct colors) for $263
 
#28 ·
Well, I just bit the bullet and got a whole module from the dealership. Little more than I thought ($314) but I'll know it's right, and I'll have a spare minus the pump just in case. Unless someone can give me a cheaper alternative, other than a chinesium one, before it comes in on Tuesday.
 
#32 · (Edited)
XDP has it for a little less than RiffRaff.

Product Font Line Screenshot Rectangle


And they show the Dorman one at the old price of the Racor. I know nothing about where this comes from.
Product Font Screenshot Software Cylinder



The Airtex on Amazon sourced from Autoplicity in the ad shows the Racor part number on the cap.

Automotive tire Screenshot Font Rim Circle
 
#34 ·
I would define a regulated input as a closed system with no fuel return, such as we use with a compressed air circuit. Pi**ing points.

A long time ago, ~2002 with the 7.3L, I put one of our test data acquisition computers in my 7.3L to measure the fuel pressure at the back of the 7.3L with the stock system and a "regulated return". From that data, there was no pressure drop at the back of the heads with the stock system compared to the front of the heads, and there was more pressure variation in the head's fuel rails with a flow-through system. Discussing that with an engineer who worked on diesel fuel systems; his explanation was diesel fuel entrained air release due to the turbulence in the rails and the spit-back from the injectors as the plunger was moving and before the check valve closed. It seemed to be a reasonable explanation. But whatever the cause, there was more variation in the fuel rail. The test was done with one head left stock and the other with the return flow setup, so there was no variation due to operating conditions, temperature, or demand.

I'm not inclined to do that.

No matter the system, volume input is always important, I agree.
 
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