Intermittent fuel problem.

[DScoville]

I am having an intermittent fuel delivery problem. It started yesterday morning as I was driving on the highway pulling a 34' fifth wheel. The truck works fine at around 10% throttle or less. As soon as you give it any more throttle it stumbles and almost dies. The rail pressure drops immediately to 2000 lbs. I changed the fuel filter with no change. Then I shut the truck down for about 15 minutes, restarted and it worked fine for the rest of the day. Now today after driving for an hour it started doing it again. There is a P0629 code. I don't have a guage on the low pressure side of the fuel system. Any help would be greatly appreciated. I am currently in Fargo ND.

 

[cerberusiam]

P0629 High Voltage Detected At The Fuel Lift Pump

Are you still running the LP in the factory location? How old is the LP?

 

[Prairie Dog]

It will do that if starving for fuel, like if your filter is clogged but with that code and the fact that you have a FASS system, I would check out the relay that came with the kit - it's probably failing. The relay is the only thing that is connected to the stock wiring that went to the LP and can throw a code like that with the FASS.

 

[DScoville]

The FASS pump I am using is the direct replacement kit and didn't come with a relay. It just plugged in to the stock plug. Since I originally posted this morning I have been driving the truck and this problem has happened twice. Both times I just turned the key off momentarily and then restarted and it worked great after that. Where is the stock fuel pump relay located? I checked in the power center under the hood and didn't see it there.

 

[DScoville]

Also, the pump is a year old with about 180,000 miles on it.

 

[cerberusiam]

Not positive but I suspect your pump is toast. The code is likely for high voltage draw at the LP, that would mean the pump is drawing too much voltage and is going bad.

 

[Prairie Dog]

P0629 "Fuel Pump Relay Circuit High, or Fuel Lift Pump Control Circuit High"
So it's either looking for a known resistance or current draw and yours is out of spec. Without a doubt your pump has failed and I would call FASS - they'll probably replace it.

 

[DScoville]

Thanks for the info guys, as soon as I get out of snow country I'll switch to my spare pump.