Noticed this condition a few times lately and its got me puzzled. Truck is experiencing a slight hesitation with acceleration when the truck is cold and not up to full operating temp. Almost like it’s a dead pedal for a split second at low rpms. Doesn't happen all the time and never after it’s warm. Scanned for codes and there wasn't any. Fuel pressure is good. (15-18 PSI). Low mileage truck (94K). VP44 is factory original. Wondered if it was Quad related, maybe the warm up mode feature I have enabled kicking in the power but it’s not. Any thoughts? 

White smoke?

No white smoke 

I'd be watching the pump honestly, sounds very much like a sticking timing piston.  

 

I'd just keep an eye on things until you have a code or more to go on.

Yeah that was my suspicion too. Thanks man. 

Re-visiting this as its happening a bit more frequently. Still mostly when the engine is cold and not up to full operating temp. Starting to think the hesitation/dead pedal I've been experiencing could be a failing TPS. Still not seeing any of the expected codes 121, 0122, 222 and 223 and there's no surging/ bucking. I guess the only way to properly diagnose its the TPS is to check the voltage drop while running?  Anyone else have 1st hand experience with diagnosing a faulty APPS/TPS?

Snap On diagnostics screen can show a dead spot. Had this happen when cold just like you and when it showed, we changed out to the Timbo APPS right then no more problems until year later when the VP gave me one hard start when already warmed up. Drove another couple thousand miles and got the VP changed. Should be carrying a Timbo APPS under the seat as they are the most reliable for the long haul.

Edited November 20, 20222 yr by JAG1

Thanks. I was leaning to picking up a Timbo. Install will be next on my list and I’m sure a new VP is in my future. 

Quick update....replaced the APPS with a Timbo and then everything seemed fine and then after a couple days the problem resurfaced briefly also only when the truck was cold. Still no CEL/codes present. I think through process of elimination that the VP is failing as was suggested earlier in this thread.  Still seems a little unusual to me to fail with low miles (97K) but the truck still is 20+ years old and $hit brakes down.  

100k miles isn't that low add to that 20+ years and I wouldn't be shocked to see the vp die.

Yeah probably need to just suck it up and get it swapped and be done with it. 

1 hour ago, Hutch24v said:

Still seems a little unusual to me to fail with low miles (97K) but the truck still is 20+ years old

 

My truck is also an '02.  The original VP44 set the P0216 code at 64,000 miles.  Drove it that way for another year (learned how to get around the limp mode).  VP44 replacement and lift pump relocation to tank was performed under warranty at 87,000 miles.  The re-manufactured VP44 installed then has now logged 283,000 miles - no 2-stroke oil and maximum lift pump pressure ever observed is 12 psi, and that's at idle.  The re-located in-tank lift pump ran for over 150,000 miles (over 11 years) at 6 psi idle and 3 psi wide open throttle.  I changed location of the in-tank lift pump to a frame mount lift for easier access in case of failure.  The in-tank lift pump never failed.

 

I think there is a wide range of quality control with re-builders.  The professional VP44 re-builders not only use new PSG' and fully test the pumps, but also use updated internal parts. 

 

- John

Great history there John. I just had a conv with DAP on the right replacement pump. The big question is if I plan to wiretap the new one with the Quad and the warranty I go with. Leaning to leave it alone and just increase injector size and run normal canbus fueling tunes. I know what’s on my Xmas list this year! 

I would opt for no wiretap and more injector.  It is so easy to tune some 7 x .010's or 7 x .011's to run nice without wiretap.

 

When the warranty is up on the pump throw some wiretap on it up top and enjoy.

Yeah. I have a set of 7x.09s from DAP on hand I’m going to install. Figure that will be within my limits of my trans rated at 450 HP. 

well within assuming you don't max wiretap.   

 

 

Also running 7 x 0.010 injectors on a stock HX35W turbo no issues. Typically run level 3 but very capable of running wire tap levels too. Final ratio will determine if EGTs get out of control. I'm running 245s (30.t inch] on 3.55 gears which makes 3.69 final ratio.

 

Just fun fact I just had my boost gauge plug blow out of the manifold and other than low power, ZERO boost and still drivable. Final ratio really changes EGTs even with no boost.