I have a 1988 f350 with a <a href="http://motorhaven.autoanything.com/">460 </a><a href="http://motorhaven.autoanything.com/">fuel injection</a>, and today after driving it in the morning, would not start. When I first trun the key I can here the pump in the tank start for about 1 second which is normal, but when i trun the key off i do not here anything. normally i would here a sound like a pump winding down over a 3 second period, and the soud would fade away.

I don't think the hi pressure pump is running. I hooked a voltmeter to it and did not see any voltage. Where does this voltage come from? the computer? how does rail pressure tell this pump when to turn on? I have replace the fuel pump relays allready.

I check presure on the rail, zipo. This happened about two weeks ago, but truck strated after some time.

So would like some info and help on troubleshooting, have all the tools.

thanks

 

Did you try to switch to the other tank? The chances both pumps going out are slim, unless you had some really dirty gasoline. I would check the inertia switch, you could bypass it just to see if it is bad, if all else fails run a jumper wire from the battery strait to the fuel pump. If the fuel pump is running, it might be a bad fuel pressure regulator or a clogged filter. I have heard that if one fuel pump goes bad, the other pump may not work correctly and may pump fuel into the other tank. Not sure about this one but keep an eye on both fuel tank gauges, it could be pumping fuel into the other tank instead of going to the engine.

 

Hello, I only have one tank. Where is the inertia switch? I didn't think trucks had them. does the high pressure pump run all the time? thanks

 

The pump should only run for about 5 seconds when you turn the key. The pump should run all the time when the engine is running. The engines crank sensor triggers it to run. The inertia switch is located on the drivers side of the fire wall to the left of the brake pedal.

 

mgm5555, It sounds like your inertia switch is fine. If the pump is running for a second or so when the key is turned on then the inertia switch hasn't been tripped. (FYI, If I remember right the inertia switch is behind the driver side kick panel).

If you checked for voltage at the pump without the truck running, then it's normal to not have power. The pump will only run continuously when the engine is running. This is because the computer knows if the engine is running or not.

The power for the pump is actually coming through the fuel pump relay which is fed via the main power distribution block under the hood. The computer sends a low voltage signal to the relay to open or close it depending on whether or not the engine is running.

Regardless, it sounds like your pump is bad, but try changing your fuel filter first just to cover your less expensive bases first. After that, put a pressure gague on the rail and cycle the key several times. (Turn key on, pause untill pump stops, key off, repeat). The goal here is to try and see how fast the pump builds full pressure, if it builds pressure at all. It should only take about two cycles to reach around 30 psi if the fuel pressure is starting at 0.

If the fuel pump checks out, you can check the regualtor by pulling the vaccum hose off and then checking fuel pressure while running. If the regulator is working, you should see around 40 psi with vaccum removed.

Hope this helps, and good luck!!!

 

Ok I replaced the fuel filter and the truck runs again. this was an intermittant problem so not a 100% sure its the filter, but the old one took some pressure to push the fuel though so hopefully this is it. Thanks everyone.

greg