dsberman94
Well-known member
sounds like theres a check ball valve that should be there and isn't or its not working properly. i've never torn an hfcm apart but that just what it sounds like.
Cleaned HFCM, now losing FP
- Thread starter 6speedsd
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swinky
New member
Sounds like cavitation.
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6speedsd
New member
I agree...it really does. But why would it be? Sucking air from some where that I can't friggen find?
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CyrusLoewen
New member
When the fuel pump shuts off on mine the pressure drops instantly almost so I don't think that is a big issue. My fuel pressure also fluctuates all the time... I might have part of the same problem or maybe that's just how some of them are.
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6speedsd
New member
Yea I get that. I know pressure drops immediately. But if I immediately recycle the key, it's like I'm trying to reprime the system...it starts at a low pressure and sloooowly comes back up. Usually doesn't even build to full pressure before the pump shuts off again.
I could look over the slight fluctuation at idle, but if I go 20% pedal, I shouldn't have a pressure drop from 60 to down in the 40's! That's not enough of a load to cause that much of a drop even on a weak pump. And pressure will drop 8-10 psi by just revving the damn thing in park.
Again, I could buy the part about some of them being like that....if mine had always been like that! Lol. This didn't start until I pulled the manifold off the HFCM and cleaned it. I had ZERO issues holding pressure before that. With the regulator set on 60psi, wot runs it wouldn't drop lower than maybe 57-58.
Go figure...a little PM work causes me nothing but headaches. I'm getting air sucked into the fuel somewhere underneath.
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I could look over the slight fluctuation at idle, but if I go 20% pedal, I shouldn't have a pressure drop from 60 to down in the 40's! That's not enough of a load to cause that much of a drop even on a weak pump. And pressure will drop 8-10 psi by just revving the damn thing in park.
Again, I could buy the part about some of them being like that....if mine had always been like that! Lol. This didn't start until I pulled the manifold off the HFCM and cleaned it. I had ZERO issues holding pressure before that. With the regulator set on 60psi, wot runs it wouldn't drop lower than maybe 57-58.
Go figure...a little PM work causes me nothing but headaches. I'm getting air sucked into the fuel somewhere underneath.
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CyrusLoewen
New member
Is there a seal or oring in that cover by the hose nipples? Could it be misplaced? Or broken somehow?
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CyrusLoewen
New member
If it's an oring on the top of the hfcm manifold it could seal when there is no pressure but could let air into the system when a suction is pulled. I don't know just shooting possibilities.
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yeah, you're on it with the air being pulled in. What a PIA for what should be simple PM. Try running the truck and spraying WD or something around the hose coupling connections on the suction side to see if its pulls the fluid in. Is your filter correct or possibly damaged? just throwing thoughts out there..
6speedsd
New member
The only Oring is the actual manifold gasket. It's new on my original hfcm. The other one I got never had the manifold taken off, so I doubt that's the issue.
Motorcraft filters, brand new as of yesterday. Not damaged...I thoroughly inspected the orings on them before install.
I thought maybe it was sucking air around the feed/suction side before the pump...that's why I ran a new hose off the feed side of the hfcm into a jug of fuel and bypassed that fitting.
I'm going to try what is did the other day again. Feed the pump from a jug of fuel, and discharge from the pump into another clear jug. That'll for sure tell me 100% this issue is hfcm related. I did it a couple days ago, but only through one pump cycle. Might do it this time and let the pump run several times. If for whatever reason it's not pumping air in the fuel, then I'll bypass the tank and that suction side fitting by running line up and into the bed of the truck to a 5gal can of fuel, and take it for a ride up the street.
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Motorcraft filters, brand new as of yesterday. Not damaged...I thoroughly inspected the orings on them before install.
I thought maybe it was sucking air around the feed/suction side before the pump...that's why I ran a new hose off the feed side of the hfcm into a jug of fuel and bypassed that fitting.
I'm going to try what is did the other day again. Feed the pump from a jug of fuel, and discharge from the pump into another clear jug. That'll for sure tell me 100% this issue is hfcm related. I did it a couple days ago, but only through one pump cycle. Might do it this time and let the pump run several times. If for whatever reason it's not pumping air in the fuel, then I'll bypass the tank and that suction side fitting by running line up and into the bed of the truck to a 5gal can of fuel, and take it for a ride up the street.
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6speedsd
New member
Ok, here is what I did. As you can see, the only factor in this is the hfcm itself.
And this is the result.
https://youtu.be/2aS_s86L0aI
It's obviously introducing air somewhere, somehow, inside that hfcm. Wondering if the new pump I got was bad out of the box.
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And this is the result.
https://youtu.be/2aS_s86L0aI
It's obviously introducing air somewhere, somehow, inside that hfcm. Wondering if the new pump I got was bad out of the box.
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sootie
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there have got to be good used HFCM's kicking around....slap one on and see how she goes?
6speedsd
New member
I got a used one locally with a bad pump. So yes, the new pump is common to both. However.....my original pump does the exact same thing....
I'm about ready to just slap a new complete hfcm assembly on it. Can get one for right at $300. Even if I put a good used one on there, I still have to worry about the condition of the pump.
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I'm about ready to just slap a new complete hfcm assembly on it. Can get one for right at $300. Even if I put a good used one on there, I still have to worry about the condition of the pump.
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6speedsd
New member
Would it be worth doing this test again with the returns looped together? Or would that not prove anything at all?
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6speedsd
New member
Did it anyways.....
Made it worse....
https://youtu.be/gKSEaXn59Jc
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Made it worse....
https://youtu.be/gKSEaXn59Jc
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6speedsd
New member
This is just sitting in park idling. Have a Marshall mechanical gauge under the hood that does the same thing.
https://youtu.be/aCHknljwV_s
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https://youtu.be/aCHknljwV_s
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6speedsd
New member
Quick trip up the road. This was at 20-21% pedal. Sorry it's so blurry. Went from 62-63psi idling to low 50's at that light pedal. More pedal drops it even faster of course....it never did any of this before the issue started.
https://youtu.be/vnfQuwrfnGY
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https://youtu.be/vnfQuwrfnGY
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Ok, here is what I did. As you can see, the only factor in this is the hfcm itself.
Anything else happen when you damaged the stock fastener and replaced it with the slotted screw? did you have to repair threads or dig something out that may have damaged the HFCM case? Its definitely sucking air.. just trying to consider everything.
6speedsd
New member
Yeah I had to retap my original for stripped threads. However, the used one I tried is causing the same issues.
After taking that pic, and the initial videos, I took the other hfcm, my new filter, and my original pump, and put it on the truck. Just for chits and grins. Exact same scenario. Doesnt matter what combination of pumps, housings, filters, caps, etc you try....always ends up with air in the fuel.
This is the part that I don't get. I could see getting a bad pump out of the box, but for it to immediately act like my old pump did? That's a hell of a coincidence you know. But what else could it be honestly? There is only so many ways to get air in the fuel in that hfcm!
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After taking that pic, and the initial videos, I took the other hfcm, my new filter, and my original pump, and put it on the truck. Just for chits and grins. Exact same scenario. Doesnt matter what combination of pumps, housings, filters, caps, etc you try....always ends up with air in the fuel.
This is the part that I don't get. I could see getting a bad pump out of the box, but for it to immediately act like my old pump did? That's a hell of a coincidence you know. But what else could it be honestly? There is only so many ways to get air in the fuel in that hfcm!
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