Hey all,

Still dealing with fuel delivery issues on my F-150.

New pumps front and rear tank, new sending unit on the rear tank. Still has OEM sending unit for front tank.

Front pump is the second I've installed since I've purchased the vehicle. The most recent one died on me completely, but had always been the reliable tank. Rear pump has never worked properly, new or old units. We've had great weather and I've been doing more diag in my free time.

I thought I might have an electrical issue causing the fuel pump(s) to get improper voltage. In my attempt to get the rear pump operational, I bypassed the PCM, Relay, Interia Switch, and tank selector with a direct battery connection. With battery voltage applied directly to the (rear) pump, I get appropriate readings on fuel pressure (55 KOEO and 40-45 KOER). When the pump is connected through its normal circuit it will reach the correct KOER pressure, but KOEO requires cycling the key many times to reach the correct pressure.

The fuel pressure readings are nice and steady regardless of throttle and within spec - for a while, until the truck is warmed up and been running. Then they fall off under heavy throttle and completely dies out under WOT. Eventually it will struggle with even a light throttle and after that, it dies completely.

I do not have a clogged fuel filter - its been replaced twice in 1,000 miles. It isn't any of the electrical connections between the pump and the battery. I feel like the only possibilities are, the pump is junk, OR I have a restriction somewhere between where the rear tank and the front tank join. Perhaps a fault fuel pressure regulator? I did not see any fuel come out of it unplugging the vacuum line. I don't want to buy yet another pump only for a fuel line to be the culprit, but really, how can I tell? Should I just go down to the front tank only? Bosch pump up front and a spectra in the rear (had to buy it to get the sending unit which was unsalvagable). The previous pump on the rear also failed in almost exactly the same way and it was a Precision branded pump from O'Reilly. Neither rear pump has been able to drive the trunk more than 5 miles out of the box.

 

You have to monitor the voltage to the pump(s) in question as you drive to verify a bad pump when it stops running.Is the pump wiring and connections in good shape? .You have tried some pretty junky pumps which I wouldn't trust.

A restriction in the line? I doubt it. There's enough pressure to feed fuel down the line.

Don't waste your money on a pressure regulator. If its not leaking, it's ok. The regulator actually keeps the pressure from going too high resulting in a rich running engine, not low pressure..

 

It's probably a bad pump then because the sending unit is new. I know that Spectra doesn't make quality pumps which is why I ordered a Bosch pump for the front tank, but I also needed a sending unit and I could only get both pump and sending unit through Spectra. Wires on the old unit were corroded in two and poorly soldered back together but of course that didn't fix it. The connector coming from the tank selector switch looks okay - hard to tell from the ground but either way I didn't see a replacement plug available except through Bronco graveyard - not going to waste my time there.

I'm not sure how I'm supposed to drive the vehicle down the road with a mess of wires hanging by the drive shaft and exhaust pipe but regardless I'm not going to replace the pump again so it doesn't matter. I'm going to eat the loss on the sending unit, drain the tank, and call it a day. Thanks for the input.



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