Weird Fuel pressure issue…

DaneGer21

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Ditto. Did you bypass the old dead in tank pump or is it still in there?
I removed the original dead pump initially when installed my in line pump, so it has been out for awhile. I had made a custom fuel pick up inside the tank, all that is still good.

I updated an old post, but here it is again…


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.
 
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DaneGer21

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I’m questioning going out to the garage to fire up the truck tonight, not because I don’t think it’ll start, it’s because it’s only -1 outside at only 7:36pm, AND my truck did NOT come with a heater when I bought it HAHA.(Which reminds me, I need to find a cheap one lol)
I stayed out of the garage, I kept warm in the man cave tonight lol, way to cold out!
 

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Gunfreak25

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Excellent! When I was having the similar issue you were, you'll remember I said I wasn't sure if the proper OEM in tank pump or the boost pump being replaced was the cure since I did both at the same time. Now after seeing your post, I'm almost sure it was that airtex I had on it. And I had it pulling from a gutted pickup not through the old pump or anything.

The Bradley's use a similar pump as the m35 but it makes 10 to 12 psi. Wish I could find one but they've become scarce and stupid expensive.
 

DaneGer21

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Excellent! When I was having the similar issue you were, you'll remember I said I wasn't sure if the proper OEM in tank pump or the boost pump being replaced was the cure since I did both at the same time. Now after seeing your post, I'm almost sure it was that airtex I had on it. And I had it pulling from a gutted pickup not through the old pump or anything.

The Bradley's use a similar pump as the m35 but it makes 10 to 12 psi. Wish I could find one but they've become scarce and stupid expensive.
Yeah my Airtex was pulling through a “custom” pickup screen, very open and non restrictive. If the product was changed like the spec sheet I have found, this is definitely an issue. The “older” e8131’s wouldn’t be an issue like must threads out there if they did in fact flow upwards of 35GPH, but the new spec at 20GPH just won’t cut it!
 

Jeepsinker

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Sooner or later we won't be able to make these boost pump repairs or find good used ones. At that point we'll be looking at using FASS type inline pumps that provide at least 40psi @ 35 gph+. Luckily there are some available in 24 volt configuration that aren't too pricey.

I am glad you found your problem eventually. Sorry I couldn't be of more help but stuff like this is hard to diagnose from the other side of the planet and 14 hours time difference.😄
 

rustystud

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Sooner or later we won't be able to make these boost pump repairs or find good used ones. At that point we'll be looking at using FASS type inline pumps that provide at least 40psi @ 35 gph+. Luckily there are some available in 24 volt configuration that aren't too pricey.

I am glad you found your problem eventually. Sorry I couldn't be of more help but stuff like this is hard to diagnose from the other side of the planet and 14 hours time difference.😄
Olympus still sells the original pump. Pricey though !!! The Airtex type pumps really don't supply enough "volume" of fuel. Yes they can provide enough pressure when there not taxed, but if you need more fuel they fall flat. MRAP pumps will work, as will several from armored units out there.
As I said years ago, the booster units are often overlooked. The seals are almost always dried out. You can use other seals as long as they fit the bore to seal it to the check valve.
Glad you found the problem though !
 

Gunfreak25

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Olympus still sells the original pump. Pricey though !!! The Airtex type pumps really don't supply enough "volume" of fuel. Yes they can provide enough pressure when there not taxed, but if you need more fuel they fall flat. MRAP pumps will work, as will several from armored units out there.
As I said years ago, the booster units are often overlooked. The seals are almost always dried out. You can use other seals as long as they fit the bore to seal it to the check valve.
Glad you found the problem though !
What's the purpose of the check valve? So far as I can surmise it really just allows fuel flow through the boost pump when the engine is off. Once started, higher pressure goes to the filters and effectively closes the little check valve. I though about welding a plug in the removable threaded check valve plug to eliminate the check valve back when I was having issues. Fuel could still flow through the boost pump but albeit slower, through the gears and such when not running.
 

Jeepsinker

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Olympus still sells the original pump. Pricey though !!! The Airtex type pumps really don't supply enough "volume" of fuel. Yes they can provide enough pressure when there not taxed, but if you need more fuel they fall flat. MRAP pumps will work, as will several from armored units out there.
As I said years ago, the booster units are often overlooked. The seals are almost always dried out. You can use other seals as long as they fit the bore to seal it to the check valve.
Glad you found the problem though !
Good to see you on here Rusty. I was mainly talking about the hard parts like the rotors and plates/ body. Just like any gear type oil pump, they all wear out eventually. I know I'm not telling you anything you don't know there. Just seems like it'll be a wise option to convert to a high performance electric diesel lift pump when the mechanical pumps aren't easy or feasible to repair or replace anymore.
 

rustystud

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Good to see you on here Rusty. I was mainly talking about the hard parts like the rotors and plates/ body. Just like any gear type oil pump, they all wear out eventually. I know I'm not telling you anything you don't know there. Just seems like it'll be a wise option to convert to a high performance electric diesel lift pump when the mechanical pumps aren't easy or feasible to repair or replace anymore.
Oh, your talking about the "boost pump" . Yeah that will start to be a problem down the road. Of course the whole engine will start to be a problem in coming up years. Injection pumps, oil pumps, gaskets, you name it. Repowering these riggs will be a new job for some people in the up-coming years. At "International Harvester Co." they had the same problem with a lot of their medium trucks. The DT466 went in a lot of trucks in the 80's .
 

rustystud

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What's the purpose of the check valve? So far as I can surmise it really just allows fuel flow through the boost pump when the engine is off. Once started, higher pressure goes to the filters and effectively closes the little check valve. I though about welding a plug in the removable threaded check valve plug to eliminate the check valve back when I was having issues. Fuel could still flow through the boost pump but albeit slower, through the gears and such when not running.
If you welded up the hole you could potentially blow up the booster pump ( blow out the seals and leak out the housing) . It needs that escape route if pressure gets to high like at freeway speeds.
 

Floridianson

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GunFreak page 24 line K right hand side LDS 465 trouble shooting manual. If you are talking about the booster pump pressure valve then it needs to be correct. You will see it starts to open at 60 psi then return pressure back to inlet side of booster pump. Now if you are talking about the system over pressure valve then that to needs to be correct. Closed when running good only open at system over pressure. Then we need the overflow valve working correct to go alone with the booster pump to develop / maintain fuel pressure at rpm. You did the right thing in this case, you rebuilt the booster if I remember.
 
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Floridianson

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Broke out the trusty TM's. Guess you have to also know if you have a mix and match booster pump. Troubleshooting manual shows the first LDS had no over pressure valve in the secondary fuel filter block. Looks like they put it in the booster pump. Then they put the over pressure in the fuel filter secondary block on the LDT's so point is need to know what booster pump you have and with mix and match. As for over pressure in system not controled one would think the old flex lines or Head O ring or booster pump would take the brunt and fail. New DOT Synflex yea they can hold a lot of pressure if lines and fittings are installed correct.
 
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