Hi all, I'm new to the forums. I recently acquired a 1991 F150 from a friend that couldn't get it to start up. He explained to me that he drove it home from work and went to start it the next day and it would turn over, but not fire. I had it towed to my house and have discovered that it is getting spark, there is voltage going to the pump (about 9V), and when you crank it over, no fuel comes out ( I disconnected the fuel line @ the fuel filter). He mentioned that he only uses the front tank because in runs rough when he uses the rear. If the pump is getting voltage, that would lead me to believe that the relays and grounds are fine, no? Any help would be appreciated, thanks in advance.

 

I'd say with that your looking at fuel pumps. It sounded like the rear is going and your front pump is gone. I'm fighting the same thing in my truck. Just my $.02

 

Sounds like you are not getting any power to the fuel pumps. You are also using the wrong testing device, set that meter aside and use a test light and you will see that the 9V is zero volts.

You need to pull the codes, post them and start from there.

 

That is a possiblity, but when the ignition was off, there was zero volts, as soon as the ignition was turned on, it jumped to 9V.

Should I put the test light at the plug for the fuel pump? there are four prongs there, which ones to test? I've also heard of an inertia switch that can shut down the fuel, is this a possibility? If so, where is that located to reset it?

 

Does not mean you have voltage there unless your battery is discharged
Yes and then at the inertia switch. See diagram below.
Yes
Not sure on a 1991, maybe in the passenger side kick panel.


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Thanks for the info man, I'll try that and get back to you.

 

i think on a 91 the inertia switch is above the steering column under the dash.

92 up it is the pass. kick panel.

 

One other thing you might want to check is the TPS (Throttle Position Sensor). If it fails so that it looks like WOT, the injectors won't turn on during start. That's not a bug, it's an undocumented (or at least hard to find) feature, as we say in the automation world. If you have no fuel pressure, yeah fuel pump/FPR. If you have pressure, and spark, but no cranky, I'd target the TPS.

 

Sorry it has taken so long to update, the truck is at my Father's house which is about 20 miles away. I checked the inertia switch with a test light and it is getting power when turning the ignition switch on. I also checked the output of the switch and when turning the ignition on, you can hear the relay click, and then the test light goes on for a second or so, and goes off. It stays on when cranking the engine, so I don't think there are any problems before the inertia switch. I then checked for power at the fuel pump harness, there was none. I'm pretty sure I had a good ground for the test light, but it didn't light in any condition. This leads me to believe that it's probably the fuel tank selector switch. That's the ony thing it could be, right?

 

Yes that or wiring and connectors.

 

you made sure that the inertia switch was not tripped, didn't you? does it even sound like the fuel pumps are trying to work?

 

yes, I made sure the switch was not tripped. In fact I even violently shook it to make it pop out, and then retested the output with a light. The light didn't show until I pushed the little red button back in. So the switch is was definitely working, but just in case, I jumpered it, and nothing changed.

As far as the pump not working.... no, neither pumps are working, but I am unsure of the condition of the rear pump. As I mentioned, it may not have been working from the get go. But the front which was previously working, is completely dead.

I thinkthe next thing to do is pull the selecor switch and test to confirm that there is power going to and from the switch to the front tank pump.

 

that is the next step i would take. let us know what happens

 

Well, I got the truck running over the weekend. Ended up being the fuel tank selector switch. I jumpered the wire for the front fuel tank and she fired right up. Unbelievable. I want to thank all of you for your help. Thanks again!

 

thanks for posting the outcome.