Engine/Transmission (1998.5 - 2002) APPS killing the VP-44?

[ThrottleJockey]

Iv'e searched the APPS subject and came up with a question.



Is it possible that the bad information the pump 'sees' from the APPS and the subsequent mistiming pulses inside the VP-44 lead to it's premature death?

 

[nps]

The ECM sees the APPS, not the VP44. While there could be some interaction, I would bet that the ECM filters any noise that may come through before commanding the VP44. Otherwise your foot could be contributing to the problem too.

 

[Gary - K7GLD]

Iv'e searched the APPS subject and came up with a question.



Is it possible that the bad information the pump 'sees' from the APPS and the subsequent mistiming pulses inside the VP-44 lead to it's premature death?

I've been trying to figure out what external sensor/control conditions might create or mimic the P0216 VP-44 error code as well - but as much past info and experience we have in this group as to VP-44 failure and replacement, a well detailed analysis and presentation of the total electronics in and around the VP operation are sadly absent.



It does seem that the VAST majority of times that code gets set, the outright failure of the VP-44 is either there or well on it's way - but sometimes, as in my case, you get the code with few if any related operating issues. Then you are left playing guessing games as to whether you are seeing an actual VP failure - or just an isolated glitch.



One that might just cost you a couple of thousand bucks!

 

[ARoss]

I recently replaced my VP and prior to throwing the death code I was having APPS problems. I nursed the truck with the CEL illuminated for a couple of months. Each time I checked the code it was the APPS voltage too low. Finally after trying everything (normal reset and resetting the voltage of the unit) I was forced to purchase a replacement. I think I may have had the replacement on for a week when I threw the death code for the first time.



I, personally, believe the APPS contributed to the demise of my VP. The symptoms were most obviously affecting my fueling. I think that prolonged malfunction can affect the VP's performance. Again, that's just my opinion! I'm sure one of the guys from II, or the like, might be able to clarify this issue ... I'd be interested to find out the facts.

 

[ThrottleJockey]

Oh yeah, nps, I see what you mean... .



... But I didn't mean noise. I was refering to CORRECT signals from the ECM at the WRONG time screwing up the pump, mistiming, etc.



Like Gary said, a crazy mix of signals from one or more FAULTY (APPS) sensors tring to fire off the electronic solenoid in the VP-44 and the cam ring not agreeing with the timing parameters or something weird like that.



I had the same set of events occur like ARoss did. Like a domino effect.

 

[nps]

I had the same set of events occur like ARoss did. Like a domino effect.

Maybe the better question is "Can a dying VP44 cause the ECM to throw APPS codes?"



Agree it is a coincidence. But all the APPS does is feed a voltage to the ECM. No different than lifting your foot off and then tromping down, or other spastic reactions to the accelerator pedal. You could replace the APPS with a potentiometer and drive by the dial if you were inclined to do so.



Could be. Don't know. Doesn't seem obvious.

 

[ThrottleJockey]

Ohh, okay. I get it. I got 'er bass ackwards!



Thanks nps. That would suck if one part of our trucks was murdering another.





But it's just me. :-laf

 

[ARoss]

Maybe the better question is "Can a dying VP44 cause the ECM to throw APPS codes?"



Agree it is a coincidence. But all the APPS does is feed a voltage to the ECM. No different than lifting your foot off and then tromping down, or other spastic reactions to the accelerator pedal. You could replace the APPS with a potentiometer and drive by the dial if you were inclined to do so.



Could be. Don't know. Doesn't seem obvious.

nps, I see what you're saying but wouldn't it adversely affect the VP if you were constantly exposing it to "spastic reactions"? Not trying to start something, just curious.

 

[nps]

nps, I see what you're saying but wouldn't it adversely affect the VP if you were constantly exposing it to "spastic reactions"? Not trying to start something, just curious.

Don't know - guess I would hope that the ECM programmer would have put some sanity limits into the program to suppress any wild inputs from any of the sensors. We know they throw codes, but other than that what else is done?



One way to tell if your APPS was really bad is to throw it back into your truck and see if it sets the code and CEL.



Like I said - don't know if the APPS could take out the VP or not. But like ThrottleJockey said, it would suck if true.

 

[ThrottleJockey]

Good call nps,



It wasn't my APPS at all. I cleaned the IAT and the MAP sensors.



Drives like a new truck.

 

[2-ND TIME]

apps signals to the vp

I did the adjust voltage of the apps to the PCM the other aaa week and the apps was putting out 70 % voltage to the ecm. I adjusted it to 98 % I lost 2% tightening it. but what a difference in the way it fuels the engine. It still bucks even down hill as well. It is undriveable up to 1700 rpm. When I punched it yesterday it actually had power at 2700 !! I replaced the ECM some years ago and it didn't do any thing different for filter the signals to it, so suspect that it isn't there for that the capacitor in the alternator and the batteries should do that. If you are having problems it is probably more then noise. The electronics are likely poor quality and leading to early demise, the quality of the parts in the vp would likely be degraded by water and contamination of the fuel. Always buy clean fuel.

 

[WardJ]

The electronics are likely poor quality and leading to early demise, the quality of the parts in the vp would likely be degraded by water and contamination of the fuel. Always buy clean fuel.

OK. . I'll bite. How do I ensure I'm buying clean fuel?