1993 Ford Ranger Pick-up Won't Start - Fuel System

Question: engine just quit while driving. Fuel pump wasn't working, so I wired 12 volts directly to it and it worked fine, i replaced it anyway. I bypassed the inertia switch and replaced the fuel pump relay and checked the fuses. I have continuous 12 volts to the relay and another 12 volts when I turn the key on, but coming out of the relay i only have 6 volts, also only 6 volts on the fuel pump. Any ideas, I'm stumped!

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Technican: Is the voltage the same(6v) coming out of both relays (try the new and old)?

Owner: yes, voltage is 6 volts from both relays. Additional information: the truck had been driven without a fuel cap for about 2 weeks; and the battery was not holding a charge. I have replaced the battery and the fuel cap to no avail. Is it possible that the relay needs more than 12 volts to make it kick power to the fuel pump? is there some selenoid that isn't working?

Technican: Does the 12 volts into the relay remain 12 when the output drops to six? Have you tried reinstalling the inertia switch? Higlight, Edit, Copy, and Paste this link into your Address bar to see a diagram of the fuel circuit. Click the 'engine wiring' diagram (to enlarge) for for your engine/year...) autozone.com/servlet/UiBroker?ForwardPage=az/cds/en_us/0900823d/80/0b/a9/c7/0900823d800ba9c7.jsp

Owner: it does remain at 12 volts, and we have checked and bypassed the inertia switch, no change. could it be the pcm? I have a scan tool, and it cannot make a connection with the computer.

Technican: What do you have for a scan tool? Connect a jumper wire from the 12v constant into the relay and the output from the relay to pump. This will check the power supply to the relay and the whole circuit from the relay to the pump. When you hot wired the pump did the truck run ok? Does the check/service engine light come on when you turn the key on (as it normally does)?

Technican: Also which engine do you have? Don't overlook all fuses. By the way, you were taking voltage readings with engine cranking?

Owner: this is a 4.0 L V6. When I jump the keyed power to the pump line, it runs the pump, but even with that shorted out, the engine will turn over but won't start, and I can hear the pump running. And no, the engine light does not come on when the key is turned. I am taking voltage readings without the engine turned over but with they key on. My scan tool is an OBD II device. Do you know where the computer is on this truck, it is not against the firewall in the engine compartment. I am thinking that teh computer is bad because it won't start with teh pump wired directly and running, the engine light does not come on, and the comptuer won't recognize the scan tool. what do you think?

Technican: Remove the passengers side kick panel (next to where a passengers foot would rest) to find the computer. Assuming the check engine light did work before it appears you have lost power to the computer or the computer is dead. Check the fuses in the power distribution box. THere should be a 30amp fuse for the computer (pcm, ecm, ecu, there are various names used).

Owner: It isn't the fuses, I checked them again. I am just going to take it to the dealer. THanks for your time anyway.

Technican: Alright, if you haven't taken it in yet check all grounds on the engine and firewall. It's always a good idea to make sure the problem is diagnosed before replacing parts. This saves money.

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