Resolved Fuel pressure high at 52 new FPR same thing

afjLX · Dec 29, 2024

Found The supply line is kinked where it goes from metal to plastic in the engine bay. So where do I get the the plastic tube from to replace it??

unkinked the line and I’m still seeing 50psi.
maybe internal damage to the plastic line is still causing restriction? I will replace and go from there I guess.

afjLX · Dec 29, 2024

Well, i unkinked the line and still showing 50psi. Maybe internal damage in the plastic line still causing issues? I will replace the line first and go from there I guess.

Noobz347 · Dec 29, 2024

Look at the entire length of your return line and ensure it's not pinched someplace.

afjLX · Dec 29, 2024

Noobz347 said:
Look at the entire length of your return line and ensure it's not pinched someplace.

Yeah I did that and don’t see any damage anywhere. Also looked at the hoses near the fuel tank and no kinks. I just removed the schrader valve at the fuel line and noticed what looks like teflon tape on it. I thought Teflon tape was bad for fuel lines as it could break down and clog up fuel systems?

Noobz347 · Dec 29, 2024

afjLX said:
Yeah I did that and don’t see any damage anywhere. Also looked at the hoses near the fuel tank and no kinks. I just removed the schrader valve at the fuel line and noticed what looks like teflon tape on it. I thought Teflon tape was bad for fuel lines as it could break down and clog up fuel systems?

For s and grins, disconnect the return line and run a length of hose into a fuel can.

Observe your fuel pressure while this new temp line is connected.

afjLX · Dec 29, 2024

Noobz347 said:
For s and grins, disconnect the return line and run a length of hose into a fuel can.

Observe your fuel pressure while this new temp line is connected.

Ok, so I just did this. Disconnected the fuel line at the return line bottom of engine bay where it goes into plastic hose from the fuel rail. Pressure was about 30psi and I was able to adjust it up to 40psi. So we are assuming now there is a clog on the return line downstream towards the tank. Would this be a valid test with it being wide open right at the fuel rail? The path of least resistance is just dumping into the bucket at that point. Should flow be that easy back into the tank? I am definitely leaning towards the cloggged return line.

Noobz347 · Dec 29, 2024

afjLX said:
Ok, so I just did this. Disconnected the fuel line at the return line bottom of engine bay where it goes into plastic hose from the fuel rail. Pressure was about 30psi and I was able to adjust it up to 40psi. So we are assuming now there is a clog on the return line downstream towards the tank. Would this be a valid test with it being wide open right at the fuel rail? The path of least resistance is just dumping into the bucket at that point. Should flow be that easy back into the tank? I am definitely leaning towards the cloggged return line.

So long as your temp return line is [after] the fuel regulator then yes... You have a restriction in your return line someplace.

AeroCoupe · Dec 29, 2024

Drop the tank. I’ve seen the lines kinked or pinched when someone doesn’t pay attention putting the tank back in.

afjLX · Dec 29, 2024

AeroCoupe said:
Drop the tank. I’ve seen the lines kinked or pinched when someone doesn’t pay attention putting the tank back in.

I just inspected the lines at the fuel tank and no kinks seen. I will have to look at the hard lines again closely and see if I missed anything. I may disconnect the line at the fuel rail and at the tank and see if I can get air through it.

afjLX · Jan 1, 2025

So I disconnected the return line at the fuel rail and dropped the tank and disconnected it at the pump. I inspected the fuel line closely from the engine to the tank and there is zero damage to the line. I blew 120psi of compressed air through the disconnected line and it blew through the no issues. Pulled the fuel pump and checked the return line and it was clear. I did end up pulling off the little rubber backflow duckbill cap/valve off the return line as it looked warped on the tip. I figured I could replace it later and test flow with it off. I reinstalled the pump, tank, and reconnected the lines. Hooked up my pressure gauge and it still reads 50psi. Zero adjustment with the regulator. So now I’m wondering could I have a clog at the injectors and testing it by dumping the fuel at the supply line disconnected was just the path of least resistance, thus allowing me to adjust the FPR.
One thing I will do first. Replace the shrader valve at the supply line test port. It looks old and kinda beat up. I also want to get another pressure gauge for a sanity check. Do this first before I go replacing injectors. Thoughts?

Noobz347 · Jan 1, 2025

How big is your fuel pump?

afjLX · Jan 1, 2025

Update 2

Gonna drop down to a walbro 190. Too much volume for my setup possibly? (Ttickflow heads, e303 cam, cobra intake). Will report back after.

afjLX · Jan 1, 2025

Noobz347 said:
How big is your fuel pump?

Walbro 255

So I’m just now finding out there is a walbro 255 low pressure and a walbro 255 high pressure. The LP is rated at 50psi while the HP is rated at 80psi. I’m wondering if I somehow was sent a HP pump by mistake?

Noobz347 · Jan 1, 2025

afjLX said:
Walbro 255

So I’m just now finding out there is a walbro 255 low pressure and a walbro 255 high pressure. The LP is rated at 50psi while the HP is rated at 80psi. I’m wondering if I somehow was sent a HP pump by mistake?

That [should] not make a difference.

I run a 255L HP for my Kenne Bell. 42 lb injectors, stock fuel regulator, lines and rails.

The only difference between the high pressure and low pressure pumps is that the high pressure resists fuel volume reduction at higher pressures.
At stock pressures, there's not real difference.

You're just not using enough fuel to justify the fuel pump and I think it is overrunning your return line.

I might try a smaller pump or running a fatter return line.

afjLX · Jan 1, 2025

Noobz347 said:
That [should] not make a difference.

I run a 255L HP for my Kenne Bell. 42 lb injectors, stock fuel regulator, lines and rails.

The only difference between the high pressure and low pressure pumps is that the high pressure resists fuel volume reduction at higher pressures.
At stock pressures, there's not real difference.

You're just not using enough fuel to justify the fuel pump and I think it is overrunning your return line.

I might try a smaller pump or running a fatter return line.

I have trick flow heads, cobra intake , e303 cam, and 24lb injectors. But no forced induction. I’ve been wondering if the pump is too big for my application. Maybe go down to 190? If I go bigger line how big should I go? Probably easier to just swap out the fuel pump for a smaller unit.

Noobz347 · Jan 1, 2025

afjLX said:
I have trick flow heads, cobra intake , e303 cam, and 24lb injectors. But no forced induction. I’ve been wondering if the pump is too big for my application. Maybe go down to 190? If I go bigger line how big should I go? Probably easier to just swap out the fuel pump for a smaller unit.

I agree.

If you take the other route though, I would go one size larger or even run a braided return line.

Both, require dropping the tank so, pick your poison.

afjLX · Jan 1, 2025

Noobz347 said:
I agree.

If you take the other route though, I would go one size larger or even run a braided return line.

Both, require dropping the tank so, pick your poison.

Reading the specs on the walbro 190, I’ve only seen them rated at 50psi. So maybe this is my issue? The 255 HP rated at 80psi is too much for my return lines.

Noobz347 · Jan 1, 2025

afjLX said:
Reading the specs on the walbro 190, I’ve only seen them rated at 50psi. So maybe this is my issue? The 255 HP rated at 80psi is too much for my return lines.

That's now how it works.

Both pumps: a 255L low pressure and a 255L high pressure will move the same amount of fuel through the same line at the same voltage and pressure.

Where they differ is when you start running them at higher pressures.

Under the same circumstances, the high pressure pump will out flow the lower pressure pump at 50 psi and even more at 80 psi.

At stock pressures, they will be the same (within tolerance).

afjLX · Jan 1, 2025

Noobz347 said:
That's now how it works.

Both pumps: a 255L low pressure and a 255L high pressure will move the same amount of fuel through the same line at the same voltage and pressure.

Where they differ is when you start running them at higher pressures.

Under the same circumstances, the high pressure pump will out flow the lower pressure pump at 50 psi and even more at 80 psi.

At stock pressures, they will be the same (within tolerance).

So then I should be able to set the fuel pressure with the 255 to 40psi?

Noobz347 · Jan 2, 2025

afjLX said:
So then I should be able to set the fuel pressure with the 255 to 40psi?

Unfortunately, no.

In my theory, your engine combo and injectors are not using enough fuel for your return line to accommodate a 255L pump. HP, LP, doesn't matter.

Your solution of a 190L I think is a good one. You need to reduce the volume you're sending to the rails because you're bypassing [too much] fuel at the regulator.

What's your engine combo? NM - I see it: Trickflow and E-303.

That's my theory and I'm sticking to it. A smaller pump should fix this.

Resolved Fuel pressure high at 52 new FPR same thing

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