Fuel Pump
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Joined: May 2002
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Fuel Pump
Hi all - Excellent forum! I've got a 93 F150 4.9 which may have a bad fuel pump, but want some opinions before I drop the tank. The truck has a bucking after engaging the clutch in the lower gears, and bogs down quit a bit when trying to accellerate on the highway.
I gave it a tune up, (new plugs, wires, rotor, dist cap, air and gas filter, oil change) and although there is more power overall, the issue is still there. So, I hooked a fuel pressure gauge up to the rail and turned the key on. The gauge went up to 35, but when the key is turned off, it drops immediatly down to 0. I pinched the return line, and tried again, but no change.
Then, I noticed that the pump would stay on at koeo, and not shut off after 2 seconds. I finally traced that to a wire which someone (maybe me awhile back, don't remember) put between the test port and ground. I removed that and the pump would then only run for 2 sec, but the pressure only goes to about 5 psi and when the pump shuts off, it drops to 0. So, hardwiring the pump I guess at least gives it the pressure to start.
Any thoughts or tips on how to be sure it's a fuel pump before buying one and dropping the tank are appreciated...
Thanks!
I gave it a tune up, (new plugs, wires, rotor, dist cap, air and gas filter, oil change) and although there is more power overall, the issue is still there. So, I hooked a fuel pressure gauge up to the rail and turned the key on. The gauge went up to 35, but when the key is turned off, it drops immediatly down to 0. I pinched the return line, and tried again, but no change.
Then, I noticed that the pump would stay on at koeo, and not shut off after 2 seconds. I finally traced that to a wire which someone (maybe me awhile back, don't remember) put between the test port and ground. I removed that and the pump would then only run for 2 sec, but the pressure only goes to about 5 psi and when the pump shuts off, it drops to 0. So, hardwiring the pump I guess at least gives it the pressure to start.
Any thoughts or tips on how to be sure it's a fuel pump before buying one and dropping the tank are appreciated...
Thanks!
Fleet Owner
Joined: Aug 2005
Posts: 23,668
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From: Easton,Ks
As you may know the 1993 had a lot of defective Fuel Pressure Regulators that would take out the check valves in the Fuel Pumps. Ford had a recall on the Pressure Regulator and would install a fix by putting in check valves in the supply lines from each tank.
On a 4.9 with the test connector ground and the key on you should have about 54 psi at the fuel rail and should hold for a little while and then after you turn the key off it should slowly drop.
I would not know if you have a bad Fuel Pressure Regulator or Check Valve in the Pump(s).
You can try pulling off the vacuum line to Regulator with it running and if fuel comes out of the vacuum connection the regulator is bad.
On a 4.9 with the test connector ground and the key on you should have about 54 psi at the fuel rail and should hold for a little while and then after you turn the key off it should slowly drop.
I would not know if you have a bad Fuel Pressure Regulator or Check Valve in the Pump(s).
You can try pulling off the vacuum line to Regulator with it running and if fuel comes out of the vacuum connection the regulator is bad.
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Thanks subford... I wasn't aware of that. This truck only has one tank. I was thinking it wasn't the regulator since pinching off the return line didn't change the results of the pressure test. I did pull the vac line off the regulator and didn't see any fuel. But, I do have a new regulator for it, so maybe I will go ahead and swap that out too, if that may be what is damaging the fuel pump. The original fuel pump was replaced about 6 years ago.
