Old as dirt,but still above it

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JamesSam

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Sam
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1987
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Silverado V10
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5.7 L 350 v8
That third fuel hose is just a vent, not a fuel return. For years pumps had two lines, fuel in, pressure out. The back side of the pump diaphragm was vented with a small hole in the case. This was how you cold tell the pump diaphragm was worn out, the pump leaked a little fuel.

Zoom ahead, EPA wants all possible fuel contained, So they added a hose barb and sent the vent back to the tank. You can just "T" the vent lines at the selector valve and use a 3 port valve.

Bucket's referral for a pump like what was installed on my, older 1974 350, no vent hose, just a breather in the case.

For anyone who thinks, "when I pulled the vent line I got fuel" here is why: The back of the pump diaphragm pulls tiny, vacuum then tiny pressure back and forth. This will make fuel or vapor draw in and out and gravity holds some. Pull the vent line and yes, some fuel comes out.
Would this work on my 1987 TBI? I am excited because this sounds so simple. Still I will have further questions. Maybe DM me?
 

Turbo4whl

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Wayne
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1974
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Jimmy
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350
Would this work on my 1987 TBI? I am excited because this sounds so simple. Still I will have further questions. Maybe DM me?
No, my reply was for @BETO 54 , he has a carburetor. I now see your truck is fuel injected. This has a fuel return. I did quote you because you asked @bucket the question. I will PM you.
 

bucket

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That third fuel hose is just a vent, not a fuel return. For years pumps had two lines, fuel in, pressure out. The back side of the pump diaphragm was vented with a small hole in the case. This was how you cold tell the pump diaphragm was worn out, the pump leaked a little fuel.

Zoom ahead, EPA wants all possible fuel contained, So they added a hose barb and sent the vent back to the tank. You can just "T" the vent lines at the selector valve and use a 3 port valve.

Bucket's referral for a pump like what was installed on my, older 1974 350, no vent hose, just a breather in the case.

For anyone who thinks, "when I pulled the vent line I got fuel" here is why: The back of the pump diaphragm pulls tiny, vacuum then tiny pressure back and forth. This will make fuel or vapor draw in and out and gravity holds some. Pull the vent line and yes, some fuel comes out.

Yes, that's what I was referring to @JamesSam
 

Long Rider

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La Grande Oregon
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Jim
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1979
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C10
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350
Welcome aboard. I have no idea how to solve your mystery. I don't admit that to just anyone.
 

Turbo4whl

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@JamesSam

Your TBI will work in a "limp home" if needed without the return line. The early TBI did not run as much fuel pressure as newer units. With out the return you will run at max pressure since regulator will have no release port. You need a fuel return with the TBI. Carburetor engines do not need a fuel return.

Here is a old chat on GMT400. Some of the guys there are knuckleheads. @HotWheelsBurban knows who I'm referring too.

TBI return line (click)
 

HotWheelsBurban

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R2500 Suburban
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@JamesSam

Your TBI will work in a "limp home" if needed without the return line. The early TBI did not run as much fuel pressure as newer units. With out the return you will run at max pressure since regulator will have no release port. You need a fuel return with the TBI. Carburetor engines do not need a fuel return.

Here is a old chat on GMT400. Some of the guys there are knuckleheads. @HotWheelsBurban knows who I'm referring too.

TBI return line (click)
Yeah we got a bunch of old cranky mechanics on there....
 

bucket

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So. After chatting with @Turbo4whl he mentioned it wouldn't work with TBI on my 1987. Are you saying it would work?

Not at all, Wayne is correct. I didn't realize you were asking about a TBI rig earlier.

@Turbo4whl do you know what the max pressure rating is for that manual 6-port valve?
 

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