Weird Fuel pressure issue…

DaneGer21

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Ok here’s my setup…

Lift pump - Airtex E8131 (commonly used!replacement)

When I turn on the main power, my pump kicks on like normal, and fuel pressure from the lift pump climbs to 6-8psi.

Then, when I start the truck, the lift pump pressure drops to 0-2psi, all while the secondary is reading 40psi at idle.


Would your opinion be that the lift pump is faulty/junk?

Would you think that the lift pump cannot keep up? It’s supposedly rated at 35GPH which is right on the money.

Or, is this normal? I’ve never noticed until now.

I’m having what I believe a fuel starvation issue while driving in higher speeds/rpm’s and wasn’t sure if it’s related or not. (For example, I can drive 100% fine, sounds good, runs good, plenty of power, go up through the gears and cruise at 45mph. After about 30secs it starts getting choked up for 3-5secs then just stalls. I coast to a stop, leave the main power on, and after about 30secs it’ll fire up. And so on, again and again.

Not sure if this issue is related to the pump pressure, or my other theory is that the wix water/fuel filter only flows a max of 12-15 GPH, which is low compared to the flows rates of 30+GPH, and “could” be choking fuel flow.

***(fuel tank was acid washed and resealed. Airtex pump was installed, it is a recommended replacement, my original was junk. All new 1/2” DOT plastic lines up to the booster pump. All new brass compression fittings. All 3 new fuel filters. Wix 24770 primary filter head, original primary setup was junk. And then a spin on Wix 33405 water/fuel separator as the new primary.)***

After all the above cleaning and replacements I only have 9miles on the truck, while having these issues. It will sit and idle beautifully, and run up through the gears beautifully, but seems like fuel flow doesn’t keep up.

Since the entire fuel system is practically BRAND new, I highly doubt plugged filters. And I’ve only run fresh diesel from the pump, with a small amount of additives.(so no nasty/oily fuels)

Thanks
 
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davidb56

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the pressure drop is normal since the IP pump is sucking the fuel on the discharge side of the Airtex pump. My deuce will run fine even without a tank pump. I ran it for 6 months that way before installing a external tank pump like yours. The water filter would be my guess as the culprit at this point as 12 GPH may be on the restrictive side (a guess again) You can get water bound fuel straight from the pump too. my truck barely gets 5 miles per gallon here in the mountains. So a 12GPH filter would really be borderline for me. Other variables would affect my MPG/GPH too.
 

DaneGer21

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Believe it was member Gunfreak thread had trouble like that. His was the IP booster pump. The over pressure valve on the secondary if it opens can cause a loss of fuel pressure if it opens when running also.
Ok I visually seen a pressure drop on my “secondary fuel gauge”. It will intermittently jump from 30-40 at idle to 0 randomly. It’ll come back randomly then go away again and again. I think this might be my starvation issue.

Should I look at the over pressure valve or the booster pump first? Probably the valve because of how easy it is.

Any other ideas? Thanks!
 

DaneGer21

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Hey, put two of those puppies in parallel output. Can't be to hard to do.
Are you thinking my lift pump may be the issue? Maybe it’s malfunctioning/dying? I know it’s the recommended replacement so I assume itcan handle the task, especially according to its specs.

Also, like mentioned above about my water/fuel seperator being restrictive, this also seems to be a recommended filter from Eastern with the spin on primary filter kit, they use a Napa 3405, and I use the WiX cross of 33405.

So either my lift pump is dying and being restrictive.

A valve is sticking open somewhere.

Booster pump is dying.
 

Floridianson

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I would think that a pressure drop when the motor starts on your in line pump would be normal. Would seem like the inline pump since it has restriction from filter / lines and booster pump it will build pressure. Now engine starts and booster kicks in and restrictions become much less and in line pump is just about flowing free and would show lower pressure. Your problem sure sounds like Gunfreak's problem with the IP booster pump. As for the over pressure valve on the secondary fillter and return line from IP is easy enough to check. The over pressure valve on the one I had was I removed the cap bolt head and under that was spring and the tappered valve that sits in a seat.
 
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DaneGer21

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Here’s what I’ve found…

First, I removed the relief valve on the secondary filters, I shimmed it and able to get pressure up to 60 at idle. But it still lost pressure shortly after. I removed the shim because the valve seemed to be responding correctly.

Next, I changed my primary filter. It held 40psi-60psi for about 4miles, and dropped out again.

After that, I left the primary filter in place, and removed the fuel line going into the booster pump. I used a 5gal jug and a stopwatch. It took 8mins 7secs to fill. Which breaks down if my math is correct, is roughly 37GPH. So plenty there it seems.

Should I dig into the booster next? What would/could cause intermittent fuel pressure loss/issues?

Thanks
 

DaneGer21

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This evening I phoned a friend for a booster pump and picked it up by dinner. Spent the last 40mins swapping them out.

I also put a very small shim back in the relief valve, it is holding steady at 48-50psi at ldle, I’ll leave that be for now.

I’ll let it get up to temp to check for leaks but so far so good. Unfortunately it’s getting late and it’s raining so a test drive will have to wait for daylight…because worst case, I don’t wanna be stuck out at night HAHA!!!
 

DaneGer21

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Well no luck. With the truck in the driveway I raised the rpm’s to 1800 and let it run versus taking to the streets. It ran beautifully for 4-5mins, then I watched the gauge on the secondaries start to bounce around and eventually went to 0psi. The trucks exhaust note changed as the fuel flow changed. After about 1mins @0psi the truck stalled out.

I left the main power on, crawled under to my primary and loosened the drain on the filter. I heard a big air release when I did. At the same time I heard my lift pump changed tones and within 3secs fuel came out of the filter drain.

It’s almost like the primary filter keeps plugging up and being sucked dry before it can refill.

I again removed the fuel line to the booster. I ran the same flow test. This time 5gals took 8mins45secs, roughly 34GPH. I grabbed another jug and did another 5gals, it jumped to 10mins30secs, roughly 28GPH.
 
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DaneGer21

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Found my issue I’m pretty sure. Weather it’s my fault, or a subpar product who knows. What I do know, is that I acid washed the fuel tank, throughly cleaned with a shop vac, let dry, and then used a product called POR15. I thought I did a pretty darn good job. I did not seal the whole inside by rotating it. I did rotate to hit all the actual tank seams and the bottom 6” where most left over fuel would sit.

Well tonight I decided to pump the rest of the fuel out of the tank, and take a peek inside. To my surprise there was some debris inside. I seen a few flakes, and then it hit me. The tank sealer is failing, ALREADY!!! I only seen 1-2 small flakes but then I reached in with an extendable magnet to scratch on the walls/bottom. It was coming off wet and disintegrating into the fuel. So that’s why I felt like I burned through a filter first thing. There’s tons of particles in the fuel.

Now what? Strip it back down with acid and clean it all back out? Then run it as is?

I thought I was doing a good thing by adding some extra protection to the bottom of the tank, ugh. What a kick in the….
 
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Gunfreak25

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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.
 

DaneGer21

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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.
Thanks for this info. I’ll definitely take a look since I now have a spare on the bench.
 

DaneGer21

Well-known member
486
794
93
Location
Creston, Ohio
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.
Also, do you know which TM would include this info or break down? Thanks!
 

Mullaney

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Found my issue I’m pretty sure. Weather it’s my fault, or a subpar product who knows. What I do know, is that I acid washed the fuel tank, throughly cleaned with a shop vac, let dry, and then used a product called POR15. I thought I did a pretty darn good job. I did not seal the whole inside by rotating it. I did rotate to hit all the actual tank seams and the bottom 6” where most left over fuel would sit.

Well tonight I decided to pump the rest of the fuel out of the tank, and take a peek inside. To my surprise there was some debris inside. I seen a few flakes, and then it hit me. The tank sealer is failing, ALREADY!!! I only seen 1-2 small flakes but then I reached in with an extendable magnet to scratch on the walls/bottom. It was coming off wet and disintegrating into the fuel. So that’s why I felt like I burned through a filter first thing. There’s tons of particles in the fuel.

Now what? Strip it back down with acid and clean it all back out? Then run it as is?

I thought I was doing a good thing by adding some extra protection to the bottom of the tank, ugh. What a kick in the….
.
There is a post somewhere on this site where somebody had found a sealer for fuel tanks. POR15 (as I understood it) was or is a rust remover. The second part after you remove all the rust you can is a sealer. I think the sealer was called Kreem possibly?
 

Gunfreak25

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They’re getting harder to find since AMBAC doesn’t make the kit anymore. South Eastern Equipment company or “seco” has them still on eBay or you can call order too. Nice folks, good parts.

I don’t recall the TM even mentioning rebuild for this part, even for the injection pump TM. But it’s super basic. Feel free to give me a call and I can help. I’ll send you my number
 
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