Fuel Pressure Loss?
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Fuel Pressure Loss?
I am using a mechanical gauge to measure fuel pressure on a stock fuel pump on a BB. I have tried both the oil filled and the non-oil filled and get the same reading problem. When cold and at idle it will read 6-8 lbs. As the engine, fuel pump etc heat up the pressure measurement drops to almost zero.
I do have a problem with the running of the engine. When fully warm and been run somewhat hard, stop and at idle it idles rough. Still runs fine, accelerates and does not fade out just a rough idle, which may tie into the falling pressure. The pump is not that old nor is the rod.
Has anyone else experienced this?.
I do have a problem with the running of the engine. When fully warm and been run somewhat hard, stop and at idle it idles rough. Still runs fine, accelerates and does not fade out just a rough idle, which may tie into the falling pressure. The pump is not that old nor is the rod.
Has anyone else experienced this?.
Thread Starter
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
What is making me lean toward the pump is this problem happens on two different Q-Jets and also on a Edelbrock carb. It seems the pump loses pressure when totally hot maybe due to the expansion of the parts inside?? Do you plan on a stock pump or something of higher volumn and go with a pressure regulator?
The other thing is I am not sure of is with an aftermarket pump ie. Edelbrock, Holley etc, how do you plumb the return line to the tank since mine has a line for that?
The other thing is I am not sure of is with an aftermarket pump ie. Edelbrock, Holley etc, how do you plumb the return line to the tank since mine has a line for that?
Drifting
Joined: May 2008
Posts: 1,647
Likes: 5
From: Roseville CA
I had this problem on my 71, but it was running out of fuel. It was a combination on the filter getting plugged and the fuel line getting kinked. I think as it ran, crap from the line would get sucked into the filter. It was one of the metal mesh filters and the crap was like sand. I think once it stopped the crap would fall out of the filter.
The other problem was the rubber line between the hard line on the frame and the pump. It had a good bend in it and when it got hot, it would bend more and pinch closed. After replacing the rubber line with the factory type S shaped one, draining some of the crap out of the tank, and replacing the filter, it's been fine.
The other problem was the rubber line between the hard line on the frame and the pump. It had a good bend in it and when it got hot, it would bend more and pinch closed. After replacing the rubber line with the factory type S shaped one, draining some of the crap out of the tank, and replacing the filter, it's been fine.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
For cars I don't drive much, I'll usually go with a Mallory electric 140 rear mounted pump/filter, and regulator/gauge at the engine. Never had any fuel delivery problems with this set up. Like this, as can fill the carb bowls before starting, and fires right up. Also have a dash switch, to stall out on empty carb bowls when parking. My car has a return line, so just put an orfice fitting in the regulator, and trickle a little fuel back to the tank, for a cool supply.
