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connor_warren59
Samba Member
Joined: March 05, 2010
Posts: 110
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 Posted: Mon Jun 30, 2025 5:33 pm Post subject: Fuel Pressure Issue |
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Hey all. I’ve got a 1982 Vanagon running a 2006 Subaru EJ253 and I’m having an issue that has me somewhat stumped.
My van isn’t maintaining fuel pressure. I swapped out the fuel pump and filter with my spares (both new). I also rebuilt my aftermarket bypass fuel pressure regulator with a new diaphragm and new seals.
I don’t know if I maybe have contaminated fuel. I backwashed my filter with fuel and immediately see an improvement in pressure on the next startup, then in the span of like a minute I go from 60psi down to about 20psi. The subsequent start up I see about 40 psi initially and then again a decrease to about 20 psi in a short matter of time.
Weird thing is I have like 100 miles on this fuel from my last fill up, so I’m not sure why it’s suddenly causing problems. I took a big sample of fuel from the tank and saw no real contamination.
Any thoughts or suggestions would be appreciated. My fuel tank is probably around 20 years old at this point, so not brand new but also not the original. |
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crazyvwvanman
Samba Member
Joined: January 28, 2008
Posts: 10366
Location: Orbiting San Diego
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| Posted: Mon Jun 30, 2025 6:09 pm Post subject: Re: Fuel Pressure Issue |
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You skipped an important test.
It is the fuel delivery test!
You unhook the return line before the tank.
You jumper the pump to run with engine off.
While watching the pressure gauge you then measure the quantity of RETURNED fuel in 30 seconds.
Pressure isn't enough, it also takes fuel volume.
On our vans the fuel pump runs 100% whenever the engine is turning.
Far more fuel is pumped than is needed by the engine at idle.
Most of the pumped fuel is RETURNED to the tank.
As engine load increases less fuel is returned to the tank as the engine uses more of it.
At maximum engine load, climbing a hill at high rpm, some fuel is still returned but much less.
So the point of the delivery test is to make sure that a lot of fuel is being pumped and most of it is being returned, all while pressure is held at spec by the pressure regulator.
Then you can know that even under max load the system can provide more than enough fuel, at the required pressure.
Mark |
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connor_warren59
Samba Member
Joined: March 05, 2010
Posts: 110
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| Posted: Tue Jul 01, 2025 9:12 am Post subject: Re: Fuel Pressure Issue |
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| I’m wondering if it could be something getting in the way/blocking the screen on the fuel pickup tube in the tank. I need to refresh the seals on my tank anyways so I’ll spend some time on it and report back in about a week |
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1988M5
Samba Member
Joined: January 23, 2016
Posts: 843
Location: Tucson, AZ
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| Posted: Tue Jul 01, 2025 9:43 am Post subject: Re: Fuel Pressure Issue |
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| crazyvwvanman wrote: |
You skipped an important test.
It is the fuel delivery test!
You unhook the return line before the tank.
You jumper the pump to run with engine off.
While watching the pressure gauge you then measure the quantity of RETURNED fuel in 30 seconds.
Pressure isn't enough, it also takes fuel volume.
On our vans the fuel pump runs 100% whenever the engine is turning.
Far more fuel is pumped than is needed by the engine at idle.
Most of the pumped fuel is RETURNED to the tank.
As engine load increases less fuel is returned to the tank as the engine uses more of it.
At maximum engine load, climbing a hill at high rpm, some fuel is still returned but much less.
So the point of the delivery test is to make sure that a lot of fuel is being pumped and most of it is being returned, all while pressure is held at spec by the pressure regulator.
Then you can know that even under max load the system can provide more than enough fuel, at the required pressure.
Mark |
Mark,
You didn't read what he wrote, he has low fuel pressure. That needs to be addressed before worrying about the volume. Cool AI stuff about the flow/volume though. This is the Samba and not some silly Google forum for answers, treat it with respect and proper information. List the feed pressure expected at idle (high vacuum), and also the pressure expected at WOT or no vacuum. A dead head reading would be cool too. The flow through volume (cc's or mili liters) would be nice also in both scenarios.
BK
PS to the OP, 86 or replace the filter to take it out of the equation of your current problem.
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs. |
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zerotofifty
Samba Member
Joined: December 27, 2003
Posts: 3750
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| Posted: Tue Jul 01, 2025 9:56 am Post subject: Re: Fuel Pressure Issue |
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| connor_warren59 wrote: |
Hey all. I’ve got a 1982 Vanagon running a 2006 Subaru EJ253 and I’m having an issue that has me somewhat stumped.
My van isn’t maintaining fuel pressure. I swapped out the fuel pump and filter with my spares (both new). I also rebuilt my aftermarket bypass fuel pressure regulator with a new diaphragm and new seals.
I don’t know if I maybe have contaminated fuel. I backwashed my filter with fuel and immediately see an improvement in pressure on the next startup, then in the span of like a minute I go from 60psi down to about 20psi. The subsequent start up I see about 40 psi initially and then again a decrease to about 20 psi in a short matter of time.
Weird thing is I have like 100 miles on this fuel from my last fill up, so I’m not sure why it’s suddenly causing problems. I took a big sample of fuel from the tank and saw no real contamination.
Any thoughts or suggestions would be appreciated. My fuel tank is probably around 20 years old at this point, so not brand new but also not the original. |
well if back wash of the filter gives a temporary improvement, that does suggest contamination.
How does the backwashed gasoline look contamination wise? Or cutting open the filter BEFORE backwash may show you the contamination as confirmation. Or simply ( well it aint so simply) remove the tank, and see whats inside. It maybe dirty, rusty.
You may also connect the pump inlet to a different gasoline container, such as a jerry can, which is known clean, and run a pressure test using a known clean fuel source. If the problem then occurs, then the issue aint a contaminated gas tank nor gas tank mesh clog.
_________________
Sorry About That Chief.
Give Peace a Chance.
Words to live by. |
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 18720
Location: Retired South Florida
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| Posted: Tue Jul 01, 2025 10:00 am Post subject: Re: Fuel Pressure Issue |
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| Is the alternator charging? Have you measured the voltage at the pump when the pressure begins to drop? Low voltage can cause the same symptom. |
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crazyvwvanman
Samba Member
Joined: January 28, 2008
Posts: 10366
Location: Orbiting San Diego
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| Posted: Tue Jul 01, 2025 10:12 am Post subject: Re: Fuel Pressure Issue |
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I read what he wrote just fine. He said he went a lot of trouble before doing the easy and needed volume delivery test which would have steered him more directly to what the actual problem is.
Of course it sounds most likely to be some kind of blockage.
The delivery test is done with the engine off and provides helpful clues that become more opaque when the engine is running and using some of the fuel.
If the pressure is low but little or nothing is coming out the return then you wouldn't need to bother swapping or rebuilding the pressure regulator.
Diagnosing rather than swapping can save time and money, even for the samba folks.
If the pump is running normally I'd next hook up a fuel can to supply the pump so as to bypass the fuel tank and see if that solves the pressure and/or volume issue.
Mark
| 1988M5 wrote: |
Mark,
You didn't read what he wrote, he has low fuel pressure. That needs to be addressed before worrying about the volume...... |
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vanagonjr
Samba Member
Joined: October 07, 2010
Posts: 3622
Location: Dartmouth, Mass.
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| Posted: Tue Jul 01, 2025 10:21 am Post subject: Re: Fuel Pressure Issue |
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[quote="crazyvwvanman"]I read what he wrote just fine. He said he went a lot of trouble before doing the easy and needed volume delivery test which would have steered him more directly to what the actual problem is.
Of course it sounds most likely to be some kind of blockage.
The delivery test is done with the engine off and provides helpful clues that become more opaque when the engine is running and using some of the fuel.
If the pressure is low but little or nothing is coming out the return then you wouldn't need to bother swapping or rebuilding the pressure regulator.
Diagnosing rather that swapping can save time and money, even for the samba folks.
Mark
[quote="1988M5"]
Mark, good info as usual!
Maybe I should ensure I have a container (even a 16oz ice tea in a glass bottle in the fridge) on long trips and a fuel pressure gauge for on the road diagnosis.
_________________
John - 86 Wolfsburg Westfalia "Weekender"
Flint reversed 1.8T W/Passat 5-Speed
LiMBO (late model bus club) www.limbobus.org
LiMBO is on Facebook too! https://www.facebook.com/groups/
FAQ thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=525798 |
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vanagonjr
Samba Member
Joined: October 07, 2010
Posts: 3622
Location: Dartmouth, Mass.
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| Posted: Tue Jul 01, 2025 10:21 am Post subject: Re: Fuel Pressure Issue |
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[quote="vanagonjr"]
| crazyvwvanman wrote: |
I read what he wrote just fine. He said he went a lot of trouble before doing the easy and needed volume delivery test which would have steered him more directly to what the actual problem is.
Of course it sounds most likely to be some kind of blockage.
The delivery test is done with the engine off and provides helpful clues that become more opaque when the engine is running and using some of the fuel.
If the pressure is low but little or nothing is coming out the return then you wouldn't need to bother swapping or rebuilding the pressure regulator.
Diagnosing rather that swapping can save time and money, even for the samba folks.
Mark
|
Mark, good info as usual!
Maybe I should ensure I have a container (even a 16oz ice tea in a glass bottle in the fridge) on long trips and a fuel pressure gauge for on the road diagnosis.
_________________
John - 86 Wolfsburg Westfalia "Weekender"
Flint reversed 1.8T W/Passat 5-Speed
LiMBO (late model bus club) www.limbobus.org
LiMBO is on Facebook too! https://www.facebook.com/groups/
FAQ thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=525798 |
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Van den Broke
Samba Member
Joined: May 20, 2012
Posts: 207
Location: Victoria, Canada
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| Posted: Tue Jul 01, 2025 3:52 pm Post subject: Re: Fuel PressureIssue |
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How are you monitoring fuel pressure while driving?
I installed a mechanical gauge temporarily in an off topic car a little while ago. Very useful diagnostic tool:
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connor_warren59
Samba Member
Joined: March 05, 2010
Posts: 110
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| Posted: Tue Jul 01, 2025 7:18 pm Post subject: Re: Fuel Pressure Issue |
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| zerotofifty wrote: |
| connor_warren59 wrote: |
Hey all. I’ve got a 1982 Vanagon running a 2006 Subaru EJ253 and I’m having an issue that has me somewhat stumped.
My van isn’t maintaining fuel pressure. I swapped out the fuel pump and filter with my spares (both new). I also rebuilt my aftermarket bypass fuel pressure regulator with a new diaphragm and new seals.
I don’t know if I maybe have contaminated fuel. I backwashed my filter with fuel and immediately see an improvement in pressure on the next startup, then in the span of like a minute I go from 60psi down to about 20psi. The subsequent start up I see about 40 psi initially and then again a decrease to about 20 psi in a short matter of time.
Weird thing is I have like 100 miles on this fuel from my last fill up, so I’m not sure why it’s suddenly causing problems. I took a big sample of fuel from the tank and saw no real contamination.
Any thoughts or suggestions would be appreciated. My fuel tank is probably around 20 years old at this point, so not brand new but also not the original. |
well if back wash of the filter gives a temporary improvement, that does suggest contamination.
How does the backwashed gasoline look contamination wise? Or cutting open the filter BEFORE backwash may show you the contamination as confirmation. Or simply ( well it aint so simply) remove the tank, and see whats inside. It maybe dirty, rusty.
You may also connect the pump inlet to a different gasoline container, such as a jerry can, which is known clean, and run a pressure test using a known clean fuel source. If the problem then occurs, then the issue aint a contaminated gas tank nor gas tank mesh clog. |
Thanks for the thoughtful response.
The fuel coming out of the filter looks fine, I don’t see any obvious contamination. But I have been wanting to cut it open to confirm.
I like your idea of just using a Jerry can with fresh gas. I feel silly for not doing that sooner. I’ll be giving that a go here once I get off work. |
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connor_warren59
Samba Member
Joined: March 05, 2010
Posts: 110
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| Posted: Tue Jul 01, 2025 7:20 pm Post subject: Re: Fuel Pressure Issue |
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| MarkWard wrote: |
| Is the alternator charging? Have you measured the voltage at the pump when the pressure begins to drop? Low voltage can cause the same symptom. |
Alternator is charging, and I’m getting 14V at the pump without any sort of voltage drop/fluctuation, but the pressure still drops. |
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connor_warren59
Samba Member
Joined: March 05, 2010
Posts: 110
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| Posted: Tue Jul 01, 2025 7:25 pm Post subject: Re: Fuel PressureIssue |
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| Van den Broke wrote: |
How are you monitoring fuel pressure while driving?
I installed a mechanical gauge temporarily in an off topic car a little while ago. Very useful diagnostic tool:
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Oh im not even driving. I’m just idling when this is happening. My fuel pressure regulator has a gauge on it at least so I can monitor what’s happening, I think if I was to drive I’d probably make it a block or two before it fell on its face and I’d be stuck pushing it home. |
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Van den Broke
Samba Member
Joined: May 20, 2012
Posts: 207
Location: Victoria, Canada
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| Posted: Tue Jul 01, 2025 7:37 pm Post subject: Re: Fuel Pressure Issue |
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| Maybe try putting a stock fuel pressure regulator on the engine. |
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dobryan
Samba Member
Joined: March 24, 2006
Posts: 17130
Location: Brookeville, MD
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MarkWard
Samba Member
Joined: February 09, 2005
Posts: 18720
Location: Retired South Florida
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| Posted: Wed Jul 02, 2025 5:43 am Post subject: Re: Fuel Pressure Issue |
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When I needed a van movable, I rigged a small fuel jug under the van with a shock cord. The supply and return went into the pour spout. Worked great. Have used it a few times to isolate fuel supply issues.
If the pump is starving for fuel, I’d expect it to be making more noise as it starves. Try crimping temporarily the return to see what max pressure is when it’s ok and dropping. |
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