Weird Fuel pressure issue…

[G744]

Another thing not mentioned so far is the tank venting.

As fuel goes out, air has to go in. Make sure the cap is set to "vent".

Otherwise your pumps can't overcome the vacuum created.

DG

 

[Mullaney]

Here’s what I used…

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That's interesting @DaneGer21 ... I didn't know that POR15 had a tank sealer.

The 1929 Model A that I have needed that problem solved. The sealer that son and I used is still as clean as it was the day we did that piece of work... It gets inspected regularly because - to be honest - I expected it to crack and there would be a tank full of chips and crumbs after a few weeks.

The tank itself in my case was loaded with rust. POR ate away most of the loose stuff, then the steam jenny blew out even more and the heat was a big plus. It got the tank too hot to handle bare handed and the water dried up. The sealer was rolled around on all sides of the tank and it seems to be holding.

 

[DaneGer21]

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That's interesting @DaneGer21 ... I didn't know that POR15 had a tank sealer.

The 1929 Model A that I have needed that problem solved. The sealer that son and I used is still as clean as it was the day we did that piece of work... It gets inspected regularly because - to be honest - I expected it to crack and there would be a tank full of chips and crumbs after a few weeks.

The tank itself in my case was loaded with rust. POR ate away most of the loose stuff, then the steam jenny blew out even more and the heat was a big plus. It got the tank too hot to handle bare handed and the water dried up. The sealer was rolled around on all sides of the tank and it seems to be holding.

POR does have a Rust remover line of product as well

 

[DaneGer21]

I contacted Seco, I have a rebuild kit headed to the house.

 

[GopherHill]

Regarding tank liners, after cleaning the crud and loose rust. Then the tank gets acid etched so the liner will stay on. Tank must be removed so you can roll it around both for acid and sealer.
For large tanks, may not be worth it.
Yrmv

 

[DaneGer21]

Regarding tank liners, after cleaning the crud and loose rust. Then the tank gets acid etched so the liner will stay on. Tank must be removed so you can roll it around both for acid and sealer.
For large tanks, may not be worth it.
Yrmv

Tank was removed. Filled and rinsed probably a dozen times. Then Acid washed(Muriatic). Air/heat dried. Shop vac’d any dust. Then lined, and rolled on garage floor.

Cleaning process took about a week. Liner was done in one evening. Liner left to dry for 2wks.

 

[Floridianson]

Well glad you got it figured. You did throw us off with saying new filters so some of us dig right in with other things that could be wrong and it was just filters / tank sealer. Guess the first post about what is wrong should be change all filters and see if that is the problem. Yea the stuff you put in the tank took out the filter but live and learn. But if you would have changed the new filter that you just put in there out you would have found the problem sooner. Myself I always had at least three filter changes sitting in the shop and always took at least one filter change in the truck I was driving just in case I had a problem on the road. Yes I learned my lesson the first time when broke down with bad filter and no extra in the truck and good thing my wrecker was just a couple of miles away. Would seem like a good little trip in any MV have a least enough filters on board to change out twice and if there is a problem and it is just filters you might just make it to where you are going instead on the side of the road. Once again glad your up and running again or figured the real problem.

 

[DaneGer21]

So my problem as Floridianson mentioned was the same as yours. I also updated all my lines to DOT 1/2 nylon, had new filters installed. I put new o rings from hardware store in my boost pump while replacing the main boost pump shaft seal which was dumping fuel in the crankcase. Fuel pressure would be be normal but once she hit 1900 to 2000 rpm it dropped to zero and stayed at zero until stopped and restarted. It would idle perfectly fine with zero fuel pressure. But any power demands caused stalling. I could hear the same Airtex I installed change pitch as the truck sat stalled and regained fuel prime after several seconds. Could have been pushing all the fuel pressure back to the tank in reverse? Who knows!

Basically the boost pump was not sealing at the internal check valve. A proper AMBAC kit installed on a better condition used booster fixed the issue. I also eliminated the AIRTEX at the same time and went back to a proper in tank military fuel pump. My Airtex never made more than 2 or 3 psi. Could have been plugged with junk or just a bad unit. But it is my feeling that they don’t flow nearly as well as the rotary vane pump. Lots of people use them without issue though so I don’t think it was the cause of my problems.

the boost pumps check valve assembly is pretty critical to proper running. There is a compressed fiber washer that seals the check valve to the piston plug, there’s also an O ring at the piston plug itself. My attempts to use hardware store fiber gaskets and o rings just wouldn’t seal properly. The check valve will appear hard and brittle because it is a phenolic resin type valve check, red in color like Bakelite. They’re usually in good shape.

So last night I pulled apart my original boost pump that I removed from the truck. There was NO fiber washer/gasket inside between the plug and valve, or anywhere for that matter. Im guessing those disintegrate over time? The o-ring on the piston plug was there and intact.

Today is in the upper 30’s so hopefully I’ll get time to reinstall it, because the next few days drop back down and then stay near 0.

And with nearly a foot of snow on the ground, I’d like to see how it does!…or just play haha

 

[DaneGer21]

So last night I pulled apart my original boost pump that I removed from the truck. There was NO fiber washer/gasket inside between the plug and valve, or anywhere for that matter. Im guessing those disintegrate over time? The o-ring on the piston plug was there and intact.

Today is in the upper 30’s so hopefully I’ll get time to reinstall it, because the next few days drop back down and then stay near 0.

And with nearly a foot of snow on the ground, I’d like to see how it does!…or just play haha

Got a chance about 15mins ago to put the newly “rebuilt” boost pump on, I used AMBAC kt9062 like mentioned above. I was given two fiber washers in my pack.

Did I get lucky? Or is there another one hiding somewhere?? Haha

Getting ready to fire the truck up in a few minutes.

 

[DaneGer21]

Negative. Still lost pressure after a few minutes of running. It would stay running while idling with zero pressure and die with the slightest throttle increase.

Inline pump took about 45secs to regain prime. During this time it took to prime, I also had the bleeder on top of my secondaries open waiting for the fuel. As soon as I heard the pump gain its prime, fuel was to me in about 2secs flats. Truck immediately fired up like normal at this point.

Why am I losing prime, or what is causing me to lose prime?
ugh…

 

[Gunfreak25]

Your boost pump is still suspect. Mine was badly scored from junk fuel at the two plate halves that sandwich together. When I put the kit on my new used pump that is when the problem was fixed. You should also check the overflow valve on the side of the hydraulic head. If stuck open there will be a big pressure drop. But being as though it’s loosing prime it makes me suspect the fuel I getting pushed back to the tank via the main supply line. I also put my military pump back in when I did the booster so it was not a definitive this or that fixed the problem per say.

In my opinion that check valve on the boost pump plug could be welded closed entirely. I don’t see the purpose behind such a fragile assembly other than to allow fuel to flow freely though the boost pump when the motor isn’t running.

may I ask what sealant you used on the booster plate when you reassembled? It is a labyrinth type machined sealing surface and any sealant used must be extremely thin.

 

[DaneGer21]

Your boost pump is still suspect. Mine was badly scored from junk fuel at the two plate halves that sandwich together. When I put the kit on my new used pump that is when the problem was fixed. You should also check the overflow valve on the side of the hydraulic head. If stuck open there will be a big pressure drop. But being as though it’s loosing prime it makes me suspect the fuel I getting pushed back to the tank via the main supply line. I also put my military pump back in when I did the booster so it was not a definitive this or that fixed the problem per say.

In my opinion that check valve on the boost pump plug could be welded closed entirely. I don’t see the purpose behind such a fragile assembly other than to allow fuel to flow freely though the boost pump when the motor isn’t running.

may I ask what sealant you used on the booster plate when you reassembled? It is a labyrinth type machined sealing surface and any sealant used must be extremely thin.

Well I installed the AMBAC kit and unfortunately it didn’t help. I’ll check all three valves again. Hard for me to believe that two boost pumps have the same issues, possible, but hard to imagine both are bad.

I used a normal fuel resistant gasket type sealer. I barely even put a film on. I watched the Tactical Repair video of his boost pump “rebuild”.

This is starting to hurt my head. How does it run PERFECT then BAM no fuel pressure, stalls, and takes about a minute to regain prime. Mind boggling

 

[smoke]

Hi Dane. I read and reread whole post. Are you working on a m35a2 or m35a3? Also is it a a3 tank or a2 fuel tank. Reason asking because if a a2 tank and you bypassed in tank pump with a external pump. What are you using for power source for pump? I'm think of three reasons if it a a2 tank. One the external pump can pull through the in tank pump until pump gets overheated from pulling through the old pump ( To much resistion going through old pump). Second thought was the rubber hose in the in tank assembly is sucking shut or collasping after some run time do to been old and wore out. If you replace it did you use the specific kind. It should be submergible type. Three reason If you used the old wire harness that went to the in tank pump. It only come with a 3 amp fuse in it. You could have a bad connect there or a bad ground cause the pump to shut off. If it a a3 tanks only thing I can thinks of is the pickup tube cracked somewhere on tube and it suck air after it runs for awhile. Is the tank completely fuel to the brim? If not I full it up to top and see if it runs long than a couple mins. If does than you know its something in the tank causing the problem. Just my thoughts.

 

[smoke]

Hi Dane. I saw your ad in wanted section for a in tank pump after posting last message. I almost guarantee you have problem pulling fuel through the old pump with the new pump. If you want to use your new pump. I would take out the old in tank pump and attach line to just the pickup screen and attach pick up screen so that stay at the bottom of the housing ( meaning staying at bottom of the tank.) Than you would have a straight shot from the bottom of tank to your new pump. If that don't work, I say your new pump is not enough to feed the injection pump at higher demand situation.

 

[DaneGer21]

Hi Dane. I saw your ad in wanted section for a in tank pump after posting last message. I almost guarantee you have problem pulling fuel through the old pump with the new pump. If you want to use your new pump. I would take out the old in tank pump and attach line to just the pickup screen and attach pick up screen so that stay at the bottom of the housing ( meaning staying at bottom of the tank.) Than you would have a straight shot from the bottom of tank to your new pump. If that don't work, I say your new pump is not enough to feed the injection pump at higher demand situation.

I am now thinking the pump may be the issue. I have found two sources for info on the Airtex E8131. A 2016 publication on their site states 10-14 psi and 35GPH. Now their site with an updated 2022 publication states 9-14psi and 20GPH.

hmmm.

I have a new Carter pump coming to try out. 6-8psi and 50gph. It also has larger 3/8” in/out compared to 1/4” on the Airtex. I will also be making some adjustments to the screen pick up

 

[DaneGer21]

First update, new pump is in, holding pressure at 50 while idle…fingers crossed…

January 25, 2022

youtube.com

Final Update…

 

[NY Tom]

Damn curious if this will be resolved.

 

[DaneGer21]

Damn curious if this will be resolved.

As of last night it was running great, even at 10 degrees outside haha By the time I let it warm up, then cruising around our farm field’s, to taking it around the block, it was a solid 35-40mins of run time, never once a hiccup. The longest it would ever run good before, was about 1-4 mins then stall, no matter how hard or easy I drove it.

I’ll fire it up again this evening, but as of now it’s good!

 

[Mullaney]

As of last night it was running great, even at 10 degrees outside haha By the time I let it warm up, then cruising around our farm field’s, to taking it around the block, it was a solid 35-40mins of run time, never once a hiccup. The longest it would ever run good before, was about 1-4 mins then stall, no matter how hard or easy I drove it.

I’ll fire it up again this evening, but as of now it’s good!

.
And maybe a short summary of what really solved the problem when you post your next update tonight?

 

[DaneGer21]

Here’s a summary…

I’ll begin by saying my truck was stalling about every 1mins-4mins. I noticed on my secondary fuel pressure gauge that I was losing fuel pressure causing it to stall. To me the truck was starving for fuel. I had changed filters a handful of times with no luck. I decided to empty the tank because I noticed some debris floating. To my surprise the tank liner was failing and chipping/pealing away. I thought ah ha, it just continues to plug my primary, filter after filter. Or so I thought. Since the tank was empty i decided to flush it again, acid washing the liner out and going from there, with no liner. After all this and a round of ALL new filters the truck still acted the same. I checked and cleaned all relief valving on the truck with no change, it continued to lose pressure and stall. I even had an in line filter BEFORE my in line pump, which I had changed also, so it’s not possible my pump was okuggedI even rebuilt the booster pump.

I decided the next possible issue was the aftermarket fuel pump I installed, an Airtex E8131. It had been recommended by many so that’s what I went with. Problem is majority of info you find states a flow rate of 35GPH, but, I found a 2022 copyright that stated 20GPH. This would absolutely cause an issue starving for fuel.

So I then decided to look for a new fuel pump. I came across and ordered a Carter 4600hp, although 12v(no biggie) it has a psi of 4.5-8’ish, and 50GPH flow and 3/8” npt inlet/outlet. I installed that pump, gave it correct voltage, and all has been fine so far.

Here is my current fuel setup…

Tank -> pick up tube -> wix 33248(prefilter) -> carter 4600hp pump -> wix filter head 24770 with wix 33405(water/fuel sep.) -> booster pump -> wix 3512(final) -> wix 3512(final) -> HH

All new 1/2” DOT plastic lines, and all new brass fittings up to the booster pump.