dukelubas

So I've been having some hesitation when I accelerate. For instance, when I'm merging onto the highway and giving it about 75% throttle, it hesitates a few times through the RPM band; just a split second hesitation as if I eased up on the pedal. This seems to be a common problem from my searches. I ordered an isolator for my APPS just in case that's the problem, but it hasn't arrived yet.

So I bought a set of Autometer fuel pressure gauges (LP and rail) to see if I can diagnose it. I have an Airdog II 165 that I installed late last year. I installed the fuel pressure probe in the service port on the Airdog. When I turn the key, I can see the gauge try to reset itself (hardly noticeable, but it does move) and it lights up with the headlights as it should, but it hasn't moved off zero. I drove to work (50 miles) and nothing. Fuel rail pressure gauge is working.

Now the other weird thing that's been happening is I don't hear the Airdog prime when I turn the key to "on" but don't start. I don't really hear it at all when the truck is running (it used to have a definite noticeable sound before) It has been doing this (or not doing this) ever since I changed the fuel filter last week. It was about 20,000 miles on the original filter and I swapped in another new filter from Airdog. After the swap, I turned the key and heard nothing. I started the truck and it ran for 15 seconds then shut off for lack of fuel. I checked the fuse to the Airdog and it had MELTED but not blown. So I changed the fuse and tried it again and this time I heard it prime. Started the truck and it ran fine.

So now I don't know what to make of the gauge reading. I can't believe the truck could possibly run without a working lift pump right? Do I believe the gauge? Can I diagnose the gauge somehow? I'll check voltage at the Airdog to make sure it's got power and I'll check my grounds, but other than that, I have no idea where else to look.

dukelubas

Nevermind, problem fixed. Gauge was fine after all. It was the AD that wasn't running right. It's running now and pressure is holding between 19 and 23 PSI depending on throttle position.

Vots

What did you find wrong with the AD?

dukelubas

I'm not sure exactly.

About a week ago, I changed the fuel filter on the AD with a filter from AD. It wouldn't prime or turn on after I tried bumping the ignition. I checked the fuse and it had melted but did not appear to blow. I replaced it and bumped the ignition a few times and it started to prime. Since then I had noticed I hadn't heard it run. I didn't think you could drive the truck without a working lift pump. It appears that you could. My gauge was reading correctly. It was actually 0 PSI because the CP3 was drawing all the fuel so it was in reality a negative fuel pressure. So I checked the fuse again and it appeared to be ok when it was plugged in but when I pulled it out you could see it too was starting to melt. So I replaced it and bumped the ignition a few times and the AD started to prime. It's been priming and running consistently now since then (a few days). The gauge now reads between 19 and 23 PSI depending on throttle position and the truck is noticeably quicker and smoother idling. I knew something was up with the AD. I'm just hoping it was some debris that worked it's way through the gerotor and it's fine now. I followed AD's instructions when changing the filter. I thought it was odd not to pre-fill the filter, but I followed the instructions to a "T".