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furgo
Samba Member
Joined: September 06, 2016
Posts: 944
Location: Southern Germany
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 Posted: Mon May 07, 2018 5:57 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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| busdaddy wrote: |
| A bus will run with 0 fuel pressure via gravity feed and manifold vacuum, it'll idle but dies when you step on the gas. The injectors still "fire", they just don't provide much fuel and the spray pattern is likely bad too. |
| raygreenwood wrote: |
| [...]. They will open and admit fuel all the way down to near 0 pressure. |
Perfect, that makes it clear, thanks!
| raygreenwood wrote: |
However...understand that with an operative pressure range of about 36-42 psi....every 1 psi of pressure is worth 2.94% to 2.38% of total fuel delivery.
So being 2-3 psi off can be significant. |
In this particular case case we're talking about no running at all (unfortunately), rather than running poorly, but nevertheless a good point.
| busdaddy wrote: |
| Have you tried priming it through a port on the S boot when you know it's going to be hard to start?, that'll decide if it's lean or has flooded itself while sitting. A trigger sprayer for household cleaners makes an excellent primer bottle. |
Yes, that will be the next step, but before I want to check the injector solenoids and the injector pulses to rule out the electrical side of things.
In any case, my fuel pressure question has been answered. I'll keep diagnosing elsewhere.
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'79 Westy, P22 interior, FI 2.0 l Federal, GE engine (hydraulic lifters)
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JaimeH 
Samba Member
Joined: April 24, 2012
Posts: 265
Location: Canterbury, NH
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| Posted: Tue Sep 11, 2018 1:37 pm Post subject: Re: Testing FI Fuel Pressure FAQ |
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Does the fuel pressure normaly fluctuate like this with the engine running? The pressure is steady with the engine stopped and the pump running with the AFM jumped.
Link
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1978 Transporter 2.0 FI, BA6
Special Thanks to Razor's Customs, Boscawen, NH |
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Urglegrew
Samba Member
Joined: February 21, 2014
Posts: 76
Location: Bay Area California
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| Posted: Tue Jan 07, 2020 9:38 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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| Quote: |
"If you pinch shut the return fuel line SLOWLY FOR ONLY A FEW SECONDS(when you are by the starter), the pressure should climb to about 4 bars or 59 psi and that will show you that the fuel pump relief valve is indeed working correctly, but your regulator is "toast". If the pressure does not rise, there is a problem with the fuel delivery system."
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If I get a spike/59 psi (my neighbor when testing said mine went up to almost 100 or so?) when pinching the hose behind the fuel pressure reg my fuel pump relief valve works but this shows that my regulator is toast? Or my regulator is toast if the pressure doesn't rise when I do this?
| Quote: |
| "If the fuel pressure is too high, you need to shuff off the engine and remove the fuel return line from the regulator and direct it into a gas can. Run the pressure test agin and if the pressure is OK, there is something blocking the return line. Low pressure compressed air or a non-sparking wire might help clean it out. The gas pumping around the fuel rail is also what keeps the fuel pump cool." |
Does this mean if I get too high of fuel pressure when I pinch the return line, or just overall when idling? |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51112
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Tue Jan 07, 2020 10:50 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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| Urglegrew wrote: |
| Quote: |
"If you pinch shut the return fuel line SLOWLY FOR ONLY A FEW SECONDS(when you are by the starter), the pressure should climb to about 4 bars or 59 psi and that will show you that the fuel pump relief valve is indeed working correctly, but your regulator is "toast". If the pressure does not rise, there is a problem with the fuel delivery system."
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If I get a spike/59 psi (my neighbor when testing said mine went up to almost 100 or so?) when pinching the hose behind the fuel pressure reg my fuel pump relief valve works but this shows that my regulator is toast? Or my regulator is toast if the pressure doesn't rise when I do this?
| Quote: |
| "If the fuel pressure is too high, you need to shuff off the engine and remove the fuel return line from the regulator and direct it into a gas can. Run the pressure test agin and if the pressure is OK, there is something blocking the return line. Low pressure compressed air or a non-sparking wire might help clean it out. The gas pumping around the fuel rail is also what keeps the fuel pump cool." |
Does this mean if I get too high of fuel pressure when I pinch the return line, or just overall when idling? |
If you got 100psi the relief valve in the pump has issues, or it's a pump from some other car that makes too much pressure or flow. If the pressure is ~30 un pinched the regulator is working.
The second quote describes what to test if the normal idling un pinched pressure is too high.
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SGKent
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Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Tue Jan 07, 2020 2:10 pm Post subject: Re: Testing FI Fuel Pressure FAQ |
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I would think that the pressure in the hose between the return nipple and the FPR will equal whatever the fuel pump will put out which is about 100 PSI. When the hose is open the pressure between the pump and FPR should be about 32 - 36 - there is a chart. But once the return is sealed then the pressure will equal whatever the pump will do. I haven't tried seeing how high and hard I can push the pump, its sort of a destructive test pushing anything to its limit to see what it can do. All it tells you is what it did this time. Don't try it in a submarine.
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sblu
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Joined: April 08, 2019
Posts: 95
Location: Austin, TX
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| Posted: Sun Dec 03, 2023 9:47 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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folks, its been quite a journey, but i've managed to replace all the fuel lines on the bus including solenoid valve + bypass as well as a one-way valve on the output of the fuel pressure valve. I tested the connections for the solenoid valve + bypass with 100PSI air to ensure no leaks. Now that everything is back in, I'd like to look for leaks throughout the entire system. Is there a clever way to have the fuel pump only on (to reduce any fire possibility) while i go about doing this?
Once the fuel lines are all intact, i can test the pressure as laid out in this thread, with the engine idling if needed.
thanks!
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1978 Westfalia Champagne Edition Project |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51112
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Dec 03, 2023 10:05 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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Disconnect the green wire points from the ignition coil and cram something into the throat of the AFM so the flap is off it's stop, pump will run when the key is on.
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Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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my59
Samba Member
Joined: August 13, 2003
Posts: 3789
Location: connecting the dots
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| Posted: Sun Dec 03, 2023 3:06 pm Post subject: Re: Testing FI Fuel Pressure FAQ |
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Adding a fuel rated shut off valve at the "C" hose location makes fuel filter changes less messy.
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my59: Well son, my grandfather died before I got to drive it, so does that answer your question?
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Other:'12 Jetta, '77 Benz 300D, and a 74 MG Midget. |
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Good Old Dusty
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Joined: September 17, 2016
Posts: 16
Location: British Columbia
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| Posted: Mon Jan 15, 2024 10:55 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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Thank you T-Cash for your excellent post on testing fuel pressure testing from September 2017. I have one question for the community. In the 1978 FI system there is a T connection in the metal fuel rail between the #3 and #4 injectors. The T connection has a 7 mm bolt in it. The bolt is unscrewed to allow for the attachment of a fuel pressure test gauge. What is the type of fitting, i.e. screw thread size and thread type required to screw into the T connection?
Thanks for your feedback. |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51112
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Jan 15, 2024 11:04 am Post subject: Re: Testing FI Fuel Pressure FAQ |
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Usually you clamp a length of 7.5mm or 5/16" fuel hose to it.
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Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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