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Discussion Starter · #1 · (Edited)
Whenever you have a low power problem you need to test the performance of the mechanical fuel pump. First of all you need a pressure tap installed in the fuel pump's outlet line. You can drill an 1/8" NPT brass "T" through its length with a 3/8" (.375") drill bit then cut the fuel pump's outlet line where you want the pressure tap located.

Before soldering the "T" in place thoroughly clean the line with a ScotchBrite pad to remove any crud, apply a good soldering flux on the line, slip the drilled brass "T" in place, then using a propane torch heat the brass "T" until you can flow 1/16" rosin core solder into the T/line connections.

After you install the "T" connect a hose and gauge to the "T" then tape the gauge to your windshield where you can easily see it. Mechanical fuel pumps often produce 5 to 6 psi at idle but under a heavy load they can fail to produce enough pressure because of their two check valves not fully closing.

With the gauge mounted to your windshield you can see what the fuel pump is doing under all driving conditions. When you see a fuel pressure drop under a heavy load/wide open throttle the fuel pump isn't keeping up with your engine's demands.

Here's a picture of my brass "T" pressure tap in my Holley's fuel line. With the "T" in place I just heated the "T" until I could flow 1/16" rosin core solder into each end.

Over the last decade I have read many complaints about new mechanical fuel pumps failing and I know why. They are using Chinese check valves that fail to fully close so the pumps have very erratic outputs.

An added note: With the birth of electronic fuel injection in the early 80's all attention shifted to the electric fuel injection and the electric fuel pumps that supplied them with fuel. At that time mechanical fuel pumps were still being used by most of the cars and pickups but by 2000 most cars and pickups were using electronic fuel injection so the manufacture of mechanical fuel pump check valves was shifted to China and that's where the trouble began; failing fuel pumps. Although most fuel pumps are still being assembled in America many of their parts come from China. Mechanical fuel pumps used to go 150,000 to 200,000 miles before giving up but now days 7,000 to 10,000 miles is common because of their lousy check valves. They may produce 5-6 psi at idle but under power their operation becomes very erratic. It's best to switch to electric fuel pumps to save yourself the hassle of dealing with the mechanical pumps.


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