I have a lifted 1996 F350 7.5L gas truck thats CC/LB. Last couple months it had a hard time starting. I thought it was a battery issue. I then hooked up my 1007 7.3L to it and after 30 min charge it start up. Then it would run great till the battery dies. I thought it'd be a great idea last week to see if the alternator was bad so i unhooked the negative to the battery. The truck then turned off so the alternator was bad. i replaced that and charged the battery. ThenI tried starting it up again, the solenoid would click but won't turn over so I got a new starter. Now the truck turns over but doesn't start. I have electricity to the spark plugs. Also some of the pos yellow and red vacuum lines broke so i replaces those and tried again. Same results so I thought i may have switched the vacuum lines around, and then I switch them around, same result as before. So, idk where to look from there. Any suggestions? I need this truck asap. Is this common for these gas trucks?

 

Have you checked the fpr? Are you getting duel to the fuel rail?

 

Fuel pumps coming on?

 

It could just be a series of coincidences that things are failing, but I guess the first thing I'd do is give it a shot of starting fluid, if it fires then you know it's fuel related. If it doesn't fire then you know it's something with the electrical.

I would suggest you go back over every wire you touched when you changed the Alternator and starter, maybe you crossed a wire or forgot a ground somewhere.

 

If it ran last week should the fuel pump still go on? And where is it located? On the engine? In the tank? On the frame? All I hear is the starter, so maybe the fuel pump is bad.

Also Im thinking of undoing everything that i did and redo it to make sure its right.

 

Turn you r key to the run position do jot try to start it and stick your head out the door and see if you hear a whine coming from the fuel tank. That's where the fuel pumps are on these beasts. You should have two tanks one pump in each. If you do not hear a whining noise fuel pump isn't coming on. Check for blown fuse. Try switching tanks and see if you get the same result.

 

Each tank has it's own high-pressure fuel pump. The pump will run for ~1 second when cycling the key from the Off to Run position. Once the engine fires the PIP signal from the distributor triggers the computer to keep the fuel pump relay energized.

If you do not hear the pump run when cycling the key from Off to Run (not start) then you need to troubleshoot the fuel supply. If the pump does run then you need to troubleshoot the ignition circuit.

Start with the basics.....fuel, spark, air

 

So heres the update. I do not hear the fuel pumps turing on (or any sort of humming) for both tanks. So theres no power to the pumps and all the fuses are fine. So I'm thinking there must be something between the fuse and the pumps?

 

Inertia switch behind the passenger side kick panel.

 

Fuel pump relays could be bad but for both to go bad at the same time? Not likely.

 

There is only one fuel pump relay....


The circuit is the same for 5.0 & 7.5L engine trucks...

 

It was a starter relay. Simple $25 fix.