I have an Air Dog II 4G 165 lift pump which contains a fuel filter and water separator, and a factory fuel filter with an integrated water separator, on my truck. The lift pump is an aftermarket component I added to help extend the life of my fuel pump (CP4, which I’ve since replaced with a CP3) and provide additional filtration and water separation, especially since I’m using an in-bed fuel tank.
On our way home from Indiana last month, I received a DIC notification for “Change Fuel Filter” and noticed a sudden loss in power while passing someone on the highway. The issue went away after a couple miles, and at the next stop I noticed that my lift pump motor was making additional noise. I figured we picked up some bad fuel at one of the stops, but went ahead and drove home since the filters seemed to do their job and catch the contaminants, at the expense of fuel pressure/ capacity. When we arrived home I changed the auxiliary filter on the lift pump and noticed that it helped, but did not entirely solve the issue with the pump motor noise. So I went ahead and ordered a replacement factory fuel filter (fuel flows into the water separator -> lift pump fuel filter -> factory fuel filter) as well as a new water separator. When I replaced the water separator, the lift pump returned to a normal volume – even though I had drained the water out of it, I guess it was clogged. Since I was working on the truck anyway, I opted to go ahead and replace the factory filter. I installed it and then the truck hesitated to start. That is a symptom of getting air in the fuel system, so I tried to bleed out the air, but the issue kept returning after 1-2 starts. I ended up buying another factory fuel filter (since they come with the seals) and replacing it again, thinking that was the issue… but it did not fix it. After that didn’t check out, I pulled the O-ring from the bleeder screw, and found a very small sliver missing from it. I bought a five pack of those bleeder screws, including the O-rings, for $15 from the auto parts store down the street, and that worked. I’m keeping one of the others in the truck as a spare from now on.
I ended up cutting the old filters open on my bandsaw and found dirt in the water separator and AirDog fuel filter, but the factory filter was clean. My best guess is that one of the diesel holding tanks at one of the stations we stopped at ruptured and had soil contamination. I’m not sure where we picked it up, because we topped off the 51 gallon transfer tank at several stops, and fed the main tank from that, to keep us from having to stop for fuel at any inconvenient time. With 87 gallons of fuel capacity, accumulated from 15 or 25 gallons at a time, it could have come from any number of sources.