Yep. This is a long post. But this is a subject I've been thinking about for a long time and I've explored it pretty thoroughly. My conclusion is that AirDog and FASS units are a solution searching for a problem and they can cause more headaches they can cure. No "miracle product" can replace proper operation and maintenance. And given the fact that the fuel system is by far the most expensive and tamper-sensitive system on a diesel vehicle, I really question why anyone would want to massively modify and "upgrade" it to increase factory performance. If the design is so good and superior to the factory system, why aren't we seeing them on new trucks and why aren't they making COMPLETE KITS to redsign the entire supply system. There are supply-pump "kits" but I'm talking about a remove-the-old-and-install-the-new system from the pickup in the fuel tank to the inlet of the injection pump for each application. There's plenty of sales potential there. They're DEFINITELY overkill for a near-stock 24-valve, because when its all said and done, putting one of them on a 24-valve pretty much negates ALL of their advantages. The extra filtration isn't required if you buy good fuel and if you install a regulator to keep the supply pressure where it's supposed to be, the big flow increase goes back to the tank and puts more air and heat in the fuel. And going the "more is better" route with fuel pressure is plain dumb on a 24-valve. According to a Dodge TSB from way back, even 30 psi at startup can damage the pump. How? is what the 25-30 psi guys say. The entire housing is full of fuel and if the pump stops in the wrong location at shutdown and the housing is completely full of 30 psi at startup, it's possible that there's no room for the pump to "stroke" and it could sieze. Which is why in a factory system the transfer pump really is doing nothing. If you install one, I'd keep the fuel pressure at 20 psi. The overflow valve is around 15 psi. That's all that's necessary to keep the pump literallly full to overflowing, and excessive flow to make additional pressure pushes more fuel through the return. That heats the fuel. Hot fuel costs power and economy and it's hard on parts. If you put an AirDog or FASS on and then have to install a regulator to keep the pressure at factory spec, which is the SMART thing to do, you've just paid $500-$700 in part alone just to replace one filter with two. Two filters located under the truck. That brings me to my favorite FASS/AirDog "advantage - it really is an advantage and they tell you so - the mounting location. If it's all done VERY well and the wiring is done VERY well and properly routed, protected and secured it would MAYBE be worth it to me for a HIGHWAY truck. On a truck that sees dirt, mud, snow, salt etc. I wouldn't want one. And I sure wouldn't want to compromise my fuel system with a bunch of extra wiring, fuel plumbing, connections, clamps, fittings etc to end up back where I started with a good factory-style lift pump - 18 psi. There's lots of horror stories about factory transfer pump failures taking out VP44s and there's been a LOT of money made fixing "problems" that really weren't there in the first place with big transfer pumps anddual filters. But I suspect that a LOT of the problems and failures are due to poor service and maintenance, crappy fuel, cheap filters, not changing the filter often enough or even changing it too often. More on that later. Not to mention running trucks out of fuel and/or trying to start the engine after a filter change or run-empty situation without bleeding the system properly first. In fact, I think that the biggest problem VP44s have is usually found at the other end of the throttle cable. Because it really is possible to "improve" or "maintain" something to the point of ruin. My cousin bought a '99 24-valve, worked the heck using it for daily driving, pulling big trailers, farm use, commercial firewood cutting and tree shearing and fence building. He's not big on "maintenance". He changed oil, greased it once in a while and kept an eye on things but mostly he just drove it and didn't mess with it any more than he had to. How long did that VP44 last? Around 350,000 miles. To be honest I think a LOT of fuel system problems in general and maybe on VP44s in particular are due to the owner messing around with the fuel system TOO MUCH. With a cannister-style filter like on our trucks, you either want to THOROUGHLY clean all around that filter cap or you WILL get dirt and debris in the cannister when you're changing the filter. How much per time depends on how neat you are. How much OVER time depends on how often you change fuel filters. And a LOT of guys change their filters WAY too often because they think it's helping their engine. If it's not done properly, it can HURT the engine. I recently changed the fuel filter on my '94 for the first time in over a year and over 25,000 miles and it was still running fine. Buy good fuel, buy good filters, install a pressure gauge to keep an eye on things and then don't don't touch the fuel system until your fuel pressure drops a few psi. THEN open the system AFTER cleaning it well, drain the water from the housing and wash out the housing if there's any debris accumated from previous filter service, install a new filter, bleed the system thoroughly by the book to minimize cranking and then let the gauge tell you when it's time to change it again. And buy good fuel. I'm a diesel mechanic, and I've seen the performance losses from dirty filters. I had a tractor one that picked up 90 HP from a simple filter change. But I also know that opening a fuel system any more than necessary is just asking for trouble AND that cool, clean fuel at the PROPER pressure is much better for the fuel system than hot, clean fuel at way too MUCH pressure. So that's my take on the 24-valve fuel system debate(s). Take it for what it's worth.
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