Do 5.0 fuel pumps vary speed by voltage?


Active Member
Jul 25, 2003
Springfield, MO
Just when I thought I had my GT fixed, now it has low fuel pressure :nonono: I have a 255 LPH In-Tank BBK fuel pump (1 year old, but has less than 5 hours of run time on it). The car is full of gas, pressure goes from 10psi initially and rises to around 22ish. Does the pressure with the 5.0 fuel pumps vary w/ voltage like some pumps I read about in the probst book? Could it be just a bad connection/bad wiring? I have it hooked through a toggle for now; the pump turns on fine, just i'm getting low pressure. The filter was also changed a year ago, but again, only has minimal run-time on it. Sound like I need a new pump?
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yes, flow rates change with voltage. i think the pump's rate is based upon an assumption of 12.6 volts.

check voltage at your toggle for a quick check. i switch could have built up resistance (esp in the summer, when stuff like that always craps out). if not, id look elsewhere.

good luck.
The pump pressure will drop with a reduction in input voltage. There is no circuitry that does this in a stock 5.0 Mustang.

The wiring inside the tank can cause problems. The installation kit for most pumps have you splicing the wires that feed the pump. I cut the old wires off and soldered new ones with new connectors. Check the quality of the ground at the black ground wire. The contact should be clean & shiny, and the wire should show no evidence of overheating.

See for a wiring diagram for your car's fuel pump.
Two ways that you can approach this. One, use a Kenne-Bell "Boost-a-Pump" that increases fuel pump voltage. Two, use a Jacob's Electronics "Accu-volt" voltage regulator for your pump...there are two models, a 14v and a 16v. I'm running a 14v unit wired up for my ignition, computer, and fuel pump.