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Old 08-09-2004, 12:51 PM   #1
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Clogged fuel return line?????......

Installed a new fuel pressure regulator diaphragm/spring yesterday to got my car running again. Origiinal diaphragm died was letting fuel leak into the plenum. However, my fuel pressure is now reading 70psi?!

I removed the AFPR assembly and reinstalled it. Still the same. I'm now checking for a clogged fuel return line.

I have removed the FPR, disconnected the flexible fuel return line from the plenum hard line and have tried blowing compressed air thru the plenum line and out the FPR return port. The air will not blow thru the line. The pressure is just building up and slipping past the tip of the air hose.

Shouldn't the air be able to blow straight thru?
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Old 08-10-2004, 09:30 PM   #2
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im not sure if i understand how you blew air through the line, but yes, the return line from the FPR to the tank should flow freely. don't try to force air backwards through the FPR. i would check the rubber line first, then with the gas cap off & with the fuel level low in the tank, see if you can blow through the metal line into the tank, it shouldn't take alot of pressure. if you find a problem check the return lines to see if they are pinched off or crushed. also i have seen a few cars with the return line clogged up with rust.

you said you have an AFPR, is the adjustment screw run down?
or is it a stock FPR?


remember, when working with the fuel system, no open flames or smoking.
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Old 08-11-2004, 09:50 AM   #3
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Quote:
Originally posted by DENN_SHAH
im not sure if i understand how you blew air through the line, but yes, the return line from the FPR to the tank should flow freely. don't try to force air backwards through the FPR. i would check the rubber line first, then with the gas cap off & with the fuel level low in the tank, see if you can blow through the metal line into the tank, it shouldn't take alot of pressure. if you find a problem check the return lines to see if they are pinched off or crushed. also i have seen a few cars with the return line clogged up with rust.

you said you have an AFPR, is the adjustment screw run down?
or is it a stock FPR?
I was trying to force air backwards thru the FPR thinking this could clear the line if it were clogged. Apparently the FPR is desigened to only let the fuel travel in one direction toward the fuel tank. I thought it might be designed that way, but I wasn't sure.

Anyway, the reason I'm focusing on the fuel rail is because I wasn't getting any fuel out the return line when I energized the fuel pump to pressurize the system.

With the rubber line disconnected, and the system pressurized, my test gauge held at 60psi and NO fuel came out the open return line. Some fuel should pour out.

The adjuster screw on the AFPR is backed all the way out.

Quote:
remember, when working with the fuel system, no open flames or smoking.
Believe me, I'm no rookie at this. I've been working on cars for 20+ years. I think most people assume everyone on TGO is 16 yrs. old and tinkering on their first car.
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Old 08-11-2004, 09:49 PM   #4
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when you had the rubber hose disconnected, did you have it disconnected where it hooks up to the return line on the car or disconnected where it hooks to the hard line from the fuel rail?
if you have no flow from the hard line & its not closed off then there is something up with your FPR, maybe the spring is out of postion.
with everything working right you should get a pretty good flow
from the return side.

i have seen some seasoned techs do some things that were not too bright at times, i have done a few myself over the years .
so, i remind others,.. even when its not needed, my boss can tell you about that, it drives him sometimes,... but like i tell him,... thats a part of my job too

Last edited by DENN_SHAH; 08-11-2004 at 09:51 PM.
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Old 08-12-2004, 12:11 AM   #5
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Re: Clogged fuel return line?????......

Quote:
Originally posted by BretD 88GTA
Installed a new fuel pressure regulator diaphragm/spring yesterday to got my car running again. Origiinal diaphragm died was letting fuel leak into the plenum. However, my fuel pressure is now reading 70psi?!

I removed the AFPR assembly and reinstalled it. Still the same. I'm now checking for a clogged fuel return line.

I have removed the FPR, disconnected the flexible fuel return line from the plenum hard line and have tried blowing compressed air thru the plenum line and out the FPR return port. The air will not blow thru the line. The pressure is just building up and slipping past the tip of the air hose.

Shouldn't the air be able to blow straight thru?
I assume the engine starts. You're concerned with the fuel system not working properly.

The FPR will flow in both directions that's why the fuel pump requires a check valve to prevent back flow.

The fact that you have 70psi at the fuel pressure port and no flow out of the passenger side fuel rail hardline indicates a clog immeadiately after, or downstream of port.

Aternately applying air pressure to each hardline should dislodge the clog, if so a thorough cleaning of the complete fuel system is desirable as the substance that's clogging the system has to come from somewhere and since it's a closed loop system it must be coming from the gas tank. I know that's not what you want to hear, the gas tank is a **** to take out, but you're car is 16+ years old.

That crud is also getting into your injectors, if they get severely clogged no amount of cleaning will get them to flow the same again, at least not for high performance. You know what happens if fuel flow goes lean when you're doing 6000+ rpm.
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Old 08-12-2004, 12:52 AM   #6
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Update:
Tonight I tried forcing air from the FPR port out the fuel rail return line. The air pressure held NO air flow.

So, I pulled the fuel rail, took it apart and found the problem. The return port on the FPR, as well about 1/4" of the return line, was blocked solid. It was kind of an off-white powdery substance, but it was packed pretty good. The rest of the return line looks clean. I also blew air thru it and the fuel rail just to be sure.

My air pressure test was the right thing to do. The return from the FPR is simply an open line, so blowing air backwards thru it is fine provided the FPR cover and diaphragm are removed.

Now I just need to pick up a new set of O-rings for the fuel rail and put it all back together. A new fuel filter will be going on as well.
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Old 11-05-2013, 08:09 PM   #7
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Re: Clogged fuel return line?????......

the return line of my fuel tank is blocked solid I have the tank out and tried getting air through the return side of the tank with no joy its so blocked when in the car the rubber hose blows of WHAT CAN I DO
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Old 11-06-2013, 08:44 AM   #8
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Re: Clogged fuel return line?????......

John, you can clean it up or replace it.
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Old 11-06-2013, 08:44 AM
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