Fuel Pumps??

[Steelman1]

I have a 1990 F150 XLT Lariat with a 4.9 IL6 EFI system. It has dual fuel tanks. The truck has been running good except for a minor low speed miss when running around 20 mph. My son borrowed the truck a couple of days ago and ran both tanks out of gas. Since then I have not been able to get the truck to run properly. I changed the in-line fuel filter, put about 4 gallon of gas in each tank and poured a pint and a half of seafoam in each tank. The truck will idle perfectly so I let it run until the gas was gone from both tanks. Twice I was able to get the truck on the road and drive about a half mile with no problems and then it started cutting out again. I did a pressure check on the fuel line at the test port and I'm not getting anything. You can remove the little valve from the port and hold your finger over it and turn the switch on and get very little gas. It just seems odd that both pumps could have gone at the same time. My truck does not have the in line high pressure pump and low pressure pumps in the tank. It only has the pumps in the tanks. I'm removing the bed now so I can get in and check voltage on the pumps and also pull the pumps and check the filters. Any help will be appreciated.

 

[blacksnapon]

Looks like you're on the right track. You should have pressure at the valve with the key on (it shuts off after 20 seconds or so).

 

[Steelman1]

What should the voltage be at the connector on the fuel pump? I have the connector off of the fuel pump. I have a black wire on the outside with 0 voltage, next is a yellow wire with a green stripe 7.82 volts, next is a black wire with a white stripe 6.63 volts and the last wire is orange with 0 volts. blacksnapon the pumps will prime for about 20 seconds when the key is turned on. The front and back tank switch appears to be working correctly since each pump will prime when selected with the switch on.

 

[Steelman1]

Checked the voltage at the fuel pump connector while wife cranked the truck and got 12 volts. Replaced the fuel pump with a new pump, same problem. So now I have a new in tank filter, new pump and new in-line filter and still no pressure at the fuel line check point.

 

[blacksnapon]

You're either sucking air, or theres a blockage in the line.

 

[dustybumpers]

Check for spark too, My 90 distributor started to go up, and it would shut the fuel pump off because it thought the truck wasn't running.