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240 Fuel flowing back into tank after shutdown

BeaverMeat

Active member
Joined
Aug 8, 2020
Location
Vancouver Island
Don?t know if it?s the return line or what but, when it shuts down I can hear fuel flowing back into the tank.

Pressure regulator, pump or check valve?
 
Gee, that is an interesting piece of information.

What?

It’s just the regular ‘81 vintage type external fuel pump. Or the was it the pressure regulator? Still learning the ins-and-outs of this thing.

Perhaps it’s normal and I never noticed it before? The return line emptying out? I thought the whole system should be pressured.
 
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What?

It’s just the regular ‘81 vintage type external fuel pump. Or the was it the pressure regulator? Still learning the ins-and-outs of this thing.

Perhaps it’s normal and I never noticed it before? The return line emptying out? I thought the whole system should be pressured.

81 K-jet cars had a pulse damper mounted on the bracket underneath next to the main (external) pump. The (control) pressure regulator was mounted under the intake
 
Well. This is a 5.0L swapped car where the Diesel fuel components were swapped for gas ones. I’ll check if there is even a check valve.

Other cause could be a faulty regulator/vacuum leak.

I’m starting think this may actually be the problem with my misfire issues
 
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It's normal to have fuel emptying to the tank after shutdown. The check valve slows down the decay of fuel pressure for easier hot starting. But it's normal for the system to empty out after shutdown. it just should take awhile like about 20 minutes to a half hour. It's called the rest pressure in a kjet system.
 
It's normal to have fuel emptying to the tank after shutdown. The check valve slows down the decay of fuel pressure for easier hot starting. But it's normal for the system to empty out after shutdown. it just should take awhile like about 20 minutes to a half hour. It's called the rest pressure in a kjet system.

Yup. It flows back immediately after shutdown and there is zero pressure in the line.
 
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Think about this for a minute guys.

The check valve is on the pressure side, the outlet of the pump.
The fuel pressure regulator determines how much fuel is returned to the tank, after fuel has run thru the rail.
There's no restriction on the return line to the tank once fuel leaves the regulator, never was, shouldn't be in this setup.
There's no way to have pressure in the return line without a restriction.

If the PRESSURE side is losing pressure, that's a different story. A quick check of fuel pressure with the engine running, then shut it off, see what happens will tell you if there's an issue on the pressure side.
 
Just to clarify what I wrote. The fuel pressure decay after shut down is slowed down by the check valve in the fuel pump. This is happening in the area between the fuel pump and the fuel pressure regulator. However, as Gary wrote, the fuel system after the regulator has now restriction so it will empty out quickly after shutdown.
 
I did the complete Fox 5.0 pulsing idle/3000rpm+ check list and ran the codes. Got a code 67 and 95.

67 is the neutral safety switch (which isn’t connected). Code 95 which is “fuel pump secondary circuit” fuel pump error. Meaning the relay didn’t kick-in the pump when the ECU told it to do so.

The car uses the Ford pump relay to run the Volvo duel pumps. So... I don’t know if it’s the swap that throws the code or of the ECU is doing it’s job.

The car primes as it should... I can hear the line pump. Perhaps my tank pump isn’t working and is throwing the code.
 
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