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Author Topic:   no fuel pressure when hot
eenfield
Dirt Maniac

Total posts: 116
posted July 04, 2005 08:34 PM  
A car I have been working on has got me stumped. When you first start it up it runs good and has fuel pressure (about 6-6 1/2lbs. But after you let let it run for a while, or until it gets hot the fuel pressure slowly goes to zero. If you start it cold, let it build pressure, then shut it down, then it will drop to zero again. (I have seen them hold pressure for days)

Heres what I have, and what I have done. The line is brand new Aeroquip -8 from a fitting in the bottom of the tank forward to the fuel pump. More -8 out to the regulator, and -8 to the carb. The regulator is a Holley 4 1/2 to 9 psi model. The pump is a new Carter 120gph/7-8 1/2 psi mechanical pump.

I have cleaned all the lines, the fuel filter, the carb, and replaced the fuel pump with another new one. I have tried adjusting the reg up and down, with only down showing any affect. I have tried using another gauge to no avail.

I will try bypassing the reg and seeing what that does. I am also thinking about feeding it fuel from another source.

Any suggestions you guys come offer up would be greatly appriciated!

-Eric-

racer17j
Dirt Forum Champ
Total posts: 5390
posted July 04, 2005 10:31 PM  
have your fuel filter in right?

eenfield
Dirt Maniac

Total posts: 116
posted July 05, 2005 06:02 PM  
Yes I have my filter in correctly...(I double checked when cleaning).

How close is too close? It is about 2 1/2-3" from the exhaust under the car and only at one point. In the engine bay it is about 4" from the headers and tolerable to hold. I kinda checked that. How would that explain the lack of pressure even when cold, or the loss of pressure when you shut it down. Both pumps that I installed were new and supposed to be 7 - 8 1/2lb. pumps.

I did notice a little fitting on the new pump that looks looks like it could take a 1/4" hose. The old pump has a hole in the casting, but no nipple. What could this be for???

racer17j
Dirt Forum Champ
Total posts: 5390
posted July 06, 2005 04:31 PM  
I agree. I had one on a street truck. No matter what i did the truck would run 220 but besides the point. It had headers with a 358 and the dude put on an electric fuel pump when it warmed up the second day i had it was vapor locking on me get it do it then take off a gas line and see if it works un hook it from the carb. Mine would go shhh and then be fine the pump was up on the frame rail called the people that made it they said no put in the back by the tank did that away from the exhaust like 6" atleast still did put a mechanical pump on it. Works good to this day.

eenfield
Dirt Maniac

Total posts: 116
posted July 09, 2005 11:56 AM  
I have checked everything but the fuel pump eccentric. Will check that today.

I wouldnt think that it is hot enough for vapor lock, because at its closest point to the exhaust I can still grab it and hold it. It is only warm to the touch.

That also does not explain why a 7 - 8 1/2lb. pump is only making 6 lbs. even with no regulator, while still cold. Arrrggg!

19J
Dirt Freak

Total posts: 370
posted July 10, 2005 08:35 PM  
I could grab mine too. And if you dont have a regulator then it sounds like you just plain have a weak pump. I bought a brand new one thinking that was it. Worked for a lil while then was junk had to put the old one back on the i switched.

Freddie
Dirt Newbie

Total posts: 2
posted July 16, 2005 01:48 AM  
Had the same problem.
Turned out to be bad needle and seat in carb.

eenfield
Dirt Maniac

Total posts: 116
posted July 16, 2005 12:29 PM  
Heres what I found... Thinking all that was left was the fuel pump eccentric (wrong) I just installed a electric pump, as the owner wanted one anyway. Plumbed it in, wired it up kicked the tire, and lit the fire. Had all the pressure I would ever want. Drove it a little bit got out and looked at the gauge...1psi, hmmmmm. Got back and noticed (finally) that the fuel lines, fittings and regulator were hotter than Hades! I checked with the infrared, and old style thermometer and got an average of 140* on the regulator. Highest was 180!!! So, to test it out I took wet rags and rapped it up, no problem.

The heat from the header, combined with the heat from the radiator fan just absolutely cooks the passenger side of the car in the corner where the heater box was. Heck you cant even touch the hood lift bracket (and that is with no hood!) Burgers anyone?

Anyway it is not my problem any more. The owner made me mad so I just turned over the car unfinished.

Thank you for all your help, and suggestions!

-Eric-

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