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Fuel lines: transitioning from hardline to flex?
#801632 February 17th 2023 8:22 pm
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BVRPLZR Offline OP
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I'm looking to swap out the bendy section of steel fuel line that attaches to my throttle body (TBI)

They're just unbelievably annoying to work with any time I have to mess with the top of the engine, and I would love to have the lines be flex from the transmission to where they connect to the throttle body.

Trying to decide between
  • AN compression fittings to transition to and from hard line, with PTFE AN in between.
  • Cut the hard-line and slip nylon tubing over it with a couple of clamps on each end


Has anyone had successes or failures with either of these methods?
They're not super different in price for me as I have access to either style of tubing where I work, so I'd just have to buy fittings.

Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #801639 February 18th 2023 11:54 am
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I know on the Dodge TBI, the fuel pressure is 14psi. There are rubber lines, but the clamps are specialized and have rolled edges.

Any mechanical fuel pump would be OK with rubber fuel line and clamps, but I'd still lat east use the special clamps if you don't go with the upgraded line.

Engine fire in a Van would get interesting real quick.


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Re: Fuel lines: transitioning from hardline to flex?
Wedgy #801681 February 20th 2023 9:20 pm
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BVRPLZR Offline OP
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I am keeping that fact in mind! haha definitely wanna do this one correctly

I'm leaning heavily towards AN line

Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #801696 February 21st 2023 8:51 am
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I 'll post a pic later I ran braided line and AN fittings tank to TBI. They make adapters to connect to the TBI. It will come down to how far you want to go. Trying to connect to old hard lines is iffy. Consider going at least all the way filter on the supply and maybe taking a chance on the return. If you ever decide to replace the tank you can always finish the rest later. I can't remember but I thought there where connections at the frame rail to go up to the engine.

Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #802509 March 26th 2023 4:40 am
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You can use regular parts store "brake line" for fuel lines. TBI fuel pressure is only around 15. I've run clamps and hose before, but usually only on each side of the filter, so I can take the whole thing off and put it in a vise or whatever to get the connectors off the filter without destroying them.

AN line would probably be overkill but also unlikely to ever wear out, so if you have access to it you may as well. Just cover it with something anywhere it might rub.


1994 G20
2002 Express, sitting dead
1988 G20 conversion, stored
Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #802536 March 27th 2023 9:58 am
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BVRPLZR Offline OP
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So I decided to just splice in some steel fuel line from the parts store and re-route it around the ignition coil.

I did this after talking with some people and the general consensus was that GM used hardline there for a reason and an engine fire in a van would be totally catastrophic and difficult to put out.

I used a tubing bender from harbor freight to get the radius and a double flare kit from the parts store to make my connection to the old hardline, where I used a flare union.


I had a small weeping leak at the fitting where the fuel pressure gauge goes so I took it all apart, cleaned it, and put it back together using Permatex #2 (this stuff is fantastic) and let it cure for a week and now I have zero leaks. Obviously it's something that i'll probably monitor regularly for a while just to be safe, but it worked out really well.

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Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #802537 March 27th 2023 10:00 am
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The first pic is of the old fuel lines with the distributor removed because otherwise it's pretty hard to see where I routed the new lines.

The 2nd and 3rd pics are of the new lines.

Nothing special, and the harbor freight bender (any the person bending the tubing, me lol) wasn't perfect, but it got the job done.

Attached Files
cut1.png (978.37 KB, 22 downloads)
cut2.jpg (238.36 KB, 23 downloads)
cut3.jpg (313.57 KB, 22 downloads)
Re: Fuel lines: transitioning from hardline to flex?
BVRPLZR #804639 June 25th 2023 4:34 am
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One of my Suburbans prior to me had the trans cooler lines replaced with hose all the way from somewhere underneath and run through a bracket on the right front of the motor on the way to the radiator. Eventually one of them rubbed through about 80 miles from home, and I had to un-plumb the add-on trans cooler to come up with enough pieces to patch it together on the side of the road. So yes good call on the hard line.


1994 G20
2002 Express, sitting dead
1988 G20 conversion, stored

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