The truck will not start, I checked the voltage at the relay and fuse and it has 12 volts. I dropped the tank and unhooked the fuel pump and sending ...

The truck will not start, I checked the voltage at the relay and fuse and it has 12 volts. I dropped the tank and unhooked the fuel pump and sending unit connectors and I only have 5 volts when the key is on. The truck was in a minor front end accident (body damage only). I also checked all of the ground wires and they are good. I also put a new fuel pump relay in. When I turn the truck on the pump will not turn on and prime and the voltage always stays at 5 volts if the key is on. Any idea guys?

I'm not exactly sure without looking at a wiring diagram how the system is set up (does the pump feed come directly from the relay, or is it run through the PCM). If it's run directly from the relay I would trace the feed wire and see if it has any signs of obvious damage or corrosion. It sounds like the feed line has a high resistance to it for some reason.

ASTE25 wrote:I'm not exactly sure without looking at a wiring diagram how the system is set up (does the pump feed come directly from the relay, or is it run through the PCM). If it's run directly from the relay I would trace the feed wire and see if it has any signs of obvious damage or corrosion. It sounds like the feed line has a high resistance to it for some reason.

Ditto on that. I don't have a wiring diagram on that but I would also look for a damaged or corroded ground, especially if it grounds right to the frame. Check it with an ohmmeter. It can look good but still have high resistance. Just fixed a Ford where the owner checked it with a test light and thought it was OK but the resistance was too high and the pump wouldn't run.

Hi guys, thanks for the reply. I have checked the grounds with an ohmmeter and they are good. I have researched this problem on google and have found a lot of trucks with the same problem, but no one has posted a solution. I am going to jump the fuel pump with 12 volts and see what happens.

I'd say it would have to be a wiring problem if the pump tests out ok.

The thing that bugs me is the fact that you get 5 volts. That sounds like it could be a reference voltage from the VCM. I'm almost wondering if it's the security system shutting off your fuel pump. Don't have the factory info but just for the heck of it if you have another key try it and see if it starts. If you've got the chip in the key sometimes it wears out and won't make contact. Could also be in the switch. Do you notice any warning on the dash like a 'security' warning that wasn't there before ? You can bypass some of the passlock systems with a close tolerance resistor but I wouldn't dare advise that without knowing exactly which system you're dealing with.

Thanks everyone for your responces. I have found out that I was checking the wrong wire connector. The 4 prong connector is for the fuel pump and sending unit. The gray wire on that 4 prong is the power for the fuel pump. I was checking the 3 prong connector. I am going to do some further test and will respond with what I find. Thanks again guys.