Wanted to get some opinions from the group on a problem I've been running into.

This is on the truck in my signature. My Airdog puts out around 22psi at idle, I haven't touched the regulator on it in at least year. Usually, this 22psi at idle works out to be around 18-19psi while cruising, then maybe drops back to 15-16 under heavy acceleration. Every once in a while, it will go on a kick where the idle pressure is the same, but the cruising pressure drops. Sometimes it will run 15 cruising and 10 under heavy load, other times a little higher. It seems to drop for a few days like that, then comes back to normal. When it was low, I tried changing fuel filters thinking maybe I had some bad fuel, but nothing changed. It would just come back in a few days.

I'm in one of those drop periods right now, but it has stayed lower than normal for a while (a couple weeks so far). Normal cruising with RPM between 1500-2000 runs right around 16psi, acceleration drops to 13-14psi. This last round seemed to happen right after a fuel-up. Starting to wonder if there is some larger debris in the tank that is partially blocking the intake screen on the pickup. And that when this happens before, it just eventually dislodges. Wasn't crazy about having to raise the bed (or drop the tank) to go on a fishing expedition, which is why I figured I'd ask here first.

What else could be my root cause? I was thinking debris, a bad spring in the regulator, or maybe an electrical problem not allowing sufficient power at load. It's all wired in using the Airdog harness and it hasn't been touched since install many years ago. Open to any other ideas I need to chase down.

 

That pressure sounds somewhat high. Where it drops too is a bit more normal. Running with the pressure too high risks damaging the diaphragm in the VP44, hopefully this isn't the case with your truck.

I had intermittent pressure issues with my DDRP pump, that I eventually tracked down to an air leak at my pre-filter. My pump was sucking air at times and slowly dropping my pressure over time, but would come back up too. It eventually became a large air leak that started making the engine run funny and later airbound the injection system. How I found it was when I tried to purge the air, the prefilter started dripping diesel fuel. Once I fixed that, the pressure came back and I was able to get the engine running again, and the pressure has been solid since.

 

Your 22 psi fuel pressure is fine. I've been running the same for the past 10 years. The window of fuel pressure desirability is always maintaining between 15-20 psi, but a couple psi either way is fine. And...there is no damageable diaphragm in the VP due to high pressures so the internet rumor is false.

That said, I would look at your fuel pressure gauge long before I'd mess with the Airdog because most fuel pressure gauges wont last on these trucks due to the hydrodynamic fluid pulses generated by the VP. Especially depending on the type and brand of gauge and how it was installed.

Also, I installed a T fitting that allowed me to retain one of the stock schrader valve fuel pressure test port fittings in the fuel pressure gauge line. I have a Vulcan fuel pressure test gauge which I can confirm my in cab pressures whenever I want.

 

Well, since your system is old - check your electrical contacts. Maybe they corroded over time.
If a dab of dielectrical grease and 10 minutes of your time does not solve the problem at least you can rule out one potential issue...

 

Thanks guys! I forgot to click the subscribe button when I posted and just made it back around to see the replies.

As for the 22psi at idle, that's just an artifact of turning up the pressure just a bit over the years when it would drop. I originally started around 19psi, then when my cruising pressure would drop I would adjust the regulator up just a bit to bring that pressure up. I just never went back to turn it down.

The fuel pressure gauge is a DiPricol mechanical. It's tapped into the fitting at the VP44 with a grease gun hose, up to a 4-way block where my idiot light sender is tapped in, then I have a needle valve on the line to the gauge. It's open just enough that I get movement on the needle when RPM changes. Since the idle pressure has stayed the same, I figured it wasn't a gauge issue, but I could be wrong.

It's oil change time, so I'll check all the electrical connections when I climb under this week.

 

Its likely the gauge. Confirm your in-cab gauge with a test gauge you can rent (borrow) at your local parts store before messing with anything, especially opening the fuel system...

 

Floating this one back to the top.

After this post last year, I had checked all the connections and made sure they were clean and that I had good connections up to the relay and to the motor. No change in pressure. I swapped out my mechanical DiPricol for a electric Isspro earlier this year and the readings were exactly the same, so it wasn't a gauge issue. I was content to leave it as is, then last week my idle pressure dropped from 22 to 17 and my cruising pressure dropped to 13-14, with acceleration falling below 10psi. So I climbed under last night (after not driving for a week) and tinkered with the regulator. I backed the regulator screw out (counting the turns), then back in to the original position. Then turned it in tighter and backed it out again to the original position. When I restarted, my pressure at idle was 27-28. So I backed it off a 1/2 turn and it dropped back to 22-23. I took it for a drive and now it holds the pressure much better. At cruise, I was still running 19-20. I'm going to back the regulator off a little more to get the idle pressure down to 20psi and leave it.

But what exactly does this indicate? Was the regulator stuck and adjusting it in/out loosened it up? Or is there another problem I should be on the lookout for? I didn't pull the regulator completely out to look at the spring and ball since I'm sitting at a full tank. I had just tried adjusting in/out based on another post I had come across a while back when looking into this.

 

Sounds like it. You may have loosed a bit of debris or cleared the regulating bits. My Isspro guage bounces around a bit but my FASS has been at 22 psi idle down to 15 at hard throttle for a long time now.

 

Thanks! Any issues with idle psi at 22psi? I'm sitting at 22-23 right now (because I haven't went back under there to dial it down a bit more). So far, it's kept my pressure over 15psi at all time, even under hard acceleration.

 

No issues...
I've been running that same fuel pressure for the last decade.

 

None that I can tell, it was set there when I installed it and I never have touched it....