Working on my old '95 F150 with the 4.9L that is going to be my daughter's first vehicle. I had diagnosed it as having a bad fuel pump a few years ago. It sat, and we finally got around to replacing both the tank and the pump last week. Hooked everything up and the pump never primes. I can feel the relay clicking, I have 12V through the fuse, 12V in and out of the inertia switch, and 12V into the tank selector switch. This truck only has one tank (rear) and there is 12V coming out of the switch on the Br/W wire. I do NOT have 12V at the Br/W wire at the pump connection. Is it a straight run through the firewall and along the frame rail for that wire between the tank selector switch and the fuel pump connector or is there some other connection point I might be missing?

Also, I went ahead and used jumper cables to put 12V on the pump directly, and I can hear it pumping. But still no fuel at the fuel rail on my gauge. After sitting for 2 years, is there something i should do to clean the lines from the tank through the filter and into the engine? A friend mentioned I could remove the filter and spary carb cleaner through the line, followed by compressed air. Any thoughts or other methods?

Thanks,
-Chris

 

Did you replace the filter?

Did the plug for the old pump fit your new pump? Or did you have to replace it with the supplied plug?

 

Brain glitch on my part - I did not replace the fuel filter before trying to fire the pump up (it's on the list).

The new pump's electrical connector fit the connector that was already in the truck - no re-wiring or splicing required.

Thanks,
-Chris

 

Verify the connector is correctly pinned. Not the first time that has happened.

 

If I remember correctly, even thou your truck only has 1 fuel tank, the main cab harness is still set up for dual tanks. Instead of a fuel selector switch, you have a jumper plug. The jumper plug would be behind the left side of the instrument bezel, where the fuel selector switch would live. Easy to check for corrosion or broken wires.

 

It has only a rear tank but the switch has 6 wires and no jumpers. I think it might have a break in the wire between the tank selector switch and where the wires come out of the firewall into the engine. I'm having a hard time figuring out if I'm checking continuity on the correct wire.

Here is the tank selector switch. I'm working with the Br/W wire that supplies 12V to the rear tank pump.



Here's the inside of the truck by brake pedal. I think wire #13 is Br/W but I don't have continuity between the wire on the switch and this wire.



Here's the engine firewall - other side of the plug in previous picture.




Am I barking up the wrong tree by checking these wires for continuity to the Br/W wire on the switch? These wire bundles are so tight I don't really see where a failure would occur on that wire in that short run so it makes me think I'm not checking the correct wire.

Thanks,
-Chris

 

You're definitely on the right path and you're doing more diagnosing than most people can do, so I'm giving you respect for that.
Yes, you should be focused on the brown and white wire that you pointed out (#789). Usually, wire breaks happen at the wire terminal, so inspect those carefully. Pull on the wire with about 5 pounds and see if the wire insulation stretches, as this will be an indication of a broken wire conductor underneath the insulation.

Was this originally a 2-tank truck?
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Thanks! At least now I know I'm on the right trail. I guess it's possible it was a 2 tank truck, but I don't see any evidence of a front tank existing previously, and the bed only has one fuel door.

Hopefully I can get back out to work on it today and post my findings.

Thanks again,
-Chris

 

Well, I believe I have isolated the 12V issue, but am not sure what the best path moving forward is. I unbolted the firewall wiring connector. Checked continuity on the Br/W wire at the tank selector switch down to the hole on the inside connector, and continuity is good. Checked continuity on the Br/W wire through the engine side connector to its pin, and continuity is good. So it seems that the continuity issue has to be in the mating of C205F hole and C205M pin on #13.



I cannot imagine replacing one or both of these given the tight space and how many short wires there are. Is it easier than I am imagining? Or should I just run a new wire from the tank selector switch through a new firewall bushing and splice it into the Br/W wire downstream? The shade tree mechanic in me leans to just running a new single wire, but since it'll by my daughter driving it daily, I don't know if I'm missing some risk in that method.

Thanks,
-Chris

 

You've done a lot of good trouble shooting. Are you sure the problem is the in the connector? Seems odd. Unless the pins are bent, it should be giving good continuity. Can you reconnect the connector and then pierce the insulation with straight pins to check the continuity between the connectors?

 

It seemed REALLY odd to me that the 2 connectors is where the break would be, too. It's raining here now, but I'll go verify my last test one more time once there's a break in the weather. I did widen the pin on the male lead of the connector by putting a razor blade in between the 3 sides of it to try to expand its contact with the female connector. I'll post back later today.

Thanks,
-Chris

 

Well, I feel dumb. I re-verified the wiring for the tank selector switch and somehow I had my tanks switched. Br/W wire is 12V for the front tank and R wire is 12V for the rear tank. At the firewall connector, the R wire turns into a different Br/W wire, that does run to the rear tank. So I have verified I have continuity from the tank selector switch R wire all the way to the fuel pump connector on the truck. I did not verify the wire at the fuel pump, but I would guess I am not looking at a 12V power issue, and it's either a ground wire issue or something in the PCM maybe? I'm going to test the ground wire at the pump and then reconnect the battery to start over, now that I know which wire is which. Argh, thank you for making me doubt my results and double check it, Proto!

 

OK, I verified the ground wire at the truck connector to the fuel pump; I do have continuity from the negative battery post to the black ground wire for the pump. Recommendation for where I go from here? Am I hooking up the battery again and seeing if I have 12V at the various connections when turning the key? Or is there something else to check first that I've missed?

Thanks again,
-Chris

 

Look at the inertia switch. I changed out a fuel pump because of that switch. Mine was the wire that plugs into the switch had corroded in the plug. Cleaned it up, and all was fine.

Was driving the truck to work everyday, and all was fine. Cranked it up to go home, and it quit before I could get it in gear to move, and there I sat, waiting on a roll back. Changed both pumps, and it still wouldn't crank. Was showing 12V to the pumps before and after the change, but the corrosion wouldn't let enough current through to run them.

Both pumps needed changing anyway, as the in-tank fuel sender didn't work, and both pumps were getting loud. Didn't want it to quit where it did though.

 

Well, definite progress today. I got my test light out to check for power at the various locations, and I found that my tank selector switch has to be set to the front tank. This sends power out on the red wire, and the darn pump started running. My fuel pressure gauge never moved off of 0. I installed the new fuel filter, and sprayed starter fluid into the air intake. It started up and died. Starter fluid again, held the throttle down part way, and the truck stayed running on its own. As soon as I let off the throttle, it dies. It will start if you press the gas pedal and let it crank for a few seconds. My fuel pressure gauge never moved off of 0 during any of this, so I am ordering a new gauge tonight and tossing the broken one.

Now I'm on to figuring out why it will not stay running unless the gas pedal is pressed. I'll be searching the forum for any common causes I can find, but feel free to throw any knowledge my way here.

This one has been a lesson in double checking results and trust, but verify, if you think you know something!