Fuel pressure relief valve

[oddshot]

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Nice job.

Clean. Green.

 

[Jeepsinker]

I appreciate that. I put a good bit of time and thought into keeping it clean looking, even relocating the return lines back behind the filter setup.

 

[rustystud]

View attachment Scan0031.pdfView attachment Scan0032.pdfView attachment Scan0033.pdfView attachment Scan0034.pdfView attachment Scan0035.pdfView attachment Scan0036.pdfSomething "Floridianson" said has been bugging me. So I went back to the TM's and tried to figure this out. The overflow valve on the pumps keeps pressure in the Hydraulic Head and allows air to escape. It also allows a small flow of fuel to keep the "HH" cool. It is not designed to prevent a fast over-pressurization of the injection pump. OK then, why does the diagram in TM 9-2815-210-35 have no pressure relief on the fuel filters like the later engines do ? After reading some more I came across this little tidbit about the fuel supply pumps used on the different models of injection pumps. Codes "A", and "F" pumps have a relief valve built into the fuel supply pump housing, while codes "B", "C" , "D", "E" and "G" pumps have no pressure relief valve in the fuel supply pump. So the military had a generic fuel pump housing built with it's own pressure valve built into it so that no matter which injection pump is used there will be no over pressurization of the fuel system. As a weird side note, the code "A" pumps where designed to be able to work with automatic transmissions. So somewhere there is or was a Multifuel engine vehicle with an automatic transmission.

 

[rustystud]

I don't remember which TM I pulled this out of, but I found it exceedingly helpful to understand what was going on.
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It even has a balloon on our particular subject here. Indicated as a fuel filter bypass. That shouldn't open until 60 or 70 psi.

I posted that a number of times already. It is from TM 9-2815-204-35 . It is used on LDS and LD engines. Also it is used on all later model multifuels.

 

[Jeepsinker]

That was very helpful rusty. And it gives me my answer. I need to retain the Prv on my LDT, but when I swap in my LDS I can remove it from the system without too much fear of I'll effect, if I read that all right. Pretty sure my LDS has a code F pump.
And, the Ford XM 656 8x8 trucks had the multifuel with an early Allison automatic. So the code A pump only came on the LDS465-2, and maybe the LDS 465-4 that we have all only seen one of... I really wanted that motor.

 

[Jeepsinker]

So I've driven my truck around with the Prv set as it is for two days now and it is running just fine. No stumbling, lack of power, or higher rpm fuel starvation signs. I still intend to shim the valve with one more tiny washer to bump the pressure up a bit more, but it is acceptable as it is until it gets up above 40 degrees outside again.

Rusty, I also spent yesterday cutting down, blasting, priming, and painting my heater box, as well as cleaning my heater core and cutting new gaskets for the box from cardboard to seal the line inlet. You weren't kidding, making the box smaller really did increase the heat output a lot! Very nice today!

 

[rustystud]

So I've driven my truck around with the Prv set as it is for two days now and it is running just fine. No stumbling, lack of power, or higher rpm fuel starvation signs. I still intend to shim the valve with one more tiny washer to bump the pressure up a bit more, but it is acceptable as it is until it gets up above 40 degrees outside again.

Rusty, I also spent yesterday cutting down, blasting, priming, and painting my heater box, as well as cleaning my heater core and cutting new gaskets for the box from cardboard to seal the line inlet. You weren't kidding, making the box smaller really did increase the heat output a lot! Very nice today!

I'm glad your truck is working fine, and with heat too ! That information about the Ford 8X8 trucks is really interesting ! I had never heard of a Multifuel with a automatic transmission. Now does anyone know where I could buy a Ford XM 656 8X8 truck ? LOL !!! Probably worth more then my total net worth ! Still, wouldn't that be so COOL to have one !!!
As far as the code "F" pump. It would work just fine without the PRV installed as it already has a 60psi relief built in.
I think I'll try your 2 micron filter set-up too Jeepsinker. It is more versatile with more filters available. I posted this before but AMBAC recommended a 2 micron filter. Since I never found a 2 micron filter I just went with the 5 micron. Thanks for sending me the link to the website !

 

[Floridianson]

Thanks Lino now I don't have to do any testing. 60 to 70 lbs makes sence. Rusty don't rember seeing your post about it but glad it's come to light again.

Jeepsinker I might leave that Filter bypass valve in the system. Was just wondering if there ever was a blockage could a to high of a pressure push fuel past the boost pump seal and into the IP/motor

 

[Jeepsinker]

Rusty, all you should have to do is change your final filter housing out for a Napa 4770 base and then drill and tap a hole in the top for a bleed screw. If you could find the base that I used for my final it would be even better, but I have had no luck tracking down so much as a part number for it, and only found one for sale used on a big truck parts site... With no part number listed. All I can tell you about it is that they came on International S1800 trucks with the 9.0l engine, and on some Caterpillar C12 engines.

 

[rustystud]

Rusty, all you should have to do is change your final filter housing out for a Napa 4770 base and then drill and tap a hole in the top for a bleed screw. If you could find the base that I used for my final it would be even better, but I have had no luck tracking down so much as a part number for it, and only found one for sale used on a big truck parts site... With no part number listed. All I can tell you about it is that they came on International S1800 trucks with the 9.0l engine, and on some Caterpillar C12 engines.

Thanks Jeepsinker. I'll try and get ahold of some friends at IHC and see if they can get a part number for me.

 

[Jeepsinker]

If you are successful let me know or post it here. There are only two filter heads on the S1800, the head with primer pump which I believe is a 7/8"-16? And there is the one that I used, which obviously has no primer and is 1"-14.

 

[Floridianson]

Hay Rusty something is got me thinking. In you post with the pics you show the relief valve and talk about no hole in one model. I believe the boost pump and it's relief valve are different from the overflow valve in the Head. The overflow valve in the Head would need the hole so as to push the air and fuel around. Maybe I miss understood you post.
When the first Mulitfuel motor came out in service did the truck have a in tank fuel pump?

 

[rustystud]

Hay Rusty something is got me thinking. In you post with the pics you show the relief valve and talk about no hole in one model. I believe the boost pump and it's relief valve are different from the overflow valve in the Head. The overflow valve in the Head would need the hole so as to push the air and fuel around. Maybe I miss understood you post.
When the first Mulitfuel motor came out in service did the truck have a in tank fuel pump?

From what I have found out there where 3 different overflow valves used. There main purpose was to allow air to escape the Hydraulic Head. The secondary purpose was to help cool the "HH" . Depending if the pump used a relief valve on the fuel boost pump determined the size of the orifice. So the overflow valves all had a hole, just different sizes. I was wrong when I said there was no hole in the later design, it was just a different size. That's why I said in the previous post your comments got me thinking and I needed to research this more. As far as I can tell, all the Multifuel engines came with an in-tank fuel pump.

 

[Jeepsinker]

So just an update on this... the past week or two I've noticed that my truck is noticeably lacking power. Idles fine, doesn't sound rough or stumble on acceleration. It just acts like I have partially clogged fuel filters all the time. I installed an oil pressure gauge today plumbed into the final fuel filter head (I had a harbor freight gauge there for a while but it failed in short order) so I've found that I still have 25 psi at idle, and only 50 psi at max rpm under load. I feel that the low pressure has damaged the hh over the last few months that I've been running it like this. I changed all the fuel filters, air filter, in tank pump is working great. Anyway, there are still several other things that could be causing this, but low fuel pressure damaging the hh is most plausible at this time.

 

[rustystud]

So just an update on this... the past week or two I've noticed that my truck is noticeably lacking power. Idles fine, doesn't sound rough or stumble on acceleration. It just acts like I have partially clogged fuel filters all the time. I installed an oil pressure gauge today plumbed into the final fuel filter head (I had a harbor freight gauge there for a while but it failed in short order) so I've found that I still have 25 psi at idle, and only 50 psi at max rpm under load. I feel that the low pressure has damaged the hh over the last few months that I've been running it like this. I changed all the fuel filters, air filter, in tank pump is working great. Anyway, there are still several other things that could be causing this, but low fuel pressure damaging the hh is most plausible at this time.

Have you checked your boost pump pressure ? Check it right at the pump. The lower pressure should not effect the Hydraulic Head. After all if that was true then just idling the engines would damage them. As long as there is fuel flowing to them they should be OK.

 

[Jeepsinker]

No I have not. I did have a very dirty fuel system for a long time ( rusty tank and filter housings). I figured I would eventually have to put an hh on it because of that anyhow. Then again, it may just be injectors getting weak again, or low compression getting bad on a couple of cylinders.

 

[rustystud]

Garrett, I just bought a relief valve today that should help everyone who goes to a spin-on filter system. It is made by "Hy-Lok" and the part number is RV1MF-4N-S316 . It has a "crack pressure" that is totally adjustable from 10psi to 300psi . The pressure is also externally adjustable so you can play with it to get just the right pressure. It is a little spendy at $140.00 but well worth it. I plan on installing it this weekend.

 

[Jeepsinker]

That looks promising, much more so than the prv 70.

 

[rustystud]

I calibrated the crack pressure to open at 70psi . I ran the truck after installing and found I got 45psi at idle, 800 rpm (previous pressure was 40psi) and 65psi at 1500 rpm (previous pressure was 55psi) . At full throttle the pressure was 70psi . This valve is far superior to the PRV valve I had installed. Sorry I let you down on this Garrett. I should have researched more relief valves instead of choosing from the first ones I had seen.

 

[Jeepsinker]

Oh it's alright buddy, just stop calling me Jared. I'm no sandwich eating child molester. My name is Garrett