Archived APPS Issue?

[Midnite]

My truck suddenly has very little power, almost like it went into limp mode. The moment it first started the check engine light came on, so as soon as I stopped I checked for codes with the key-on-off-on-off-on method, and it showed only P1693--no others.

I've cleaned my IAT and MAP sensors just for the heck of it, but that fixed nothing. Could the problem be my APPS? I wouldn't have thought so because it seems like most people who've posted about their APPS problems also indicate they had other codes set besides P1693. I'm just not sure what else to check.

If it makes a difference, in the morning when the engine is cold it'll act like it has normal power, but then start to intermittantly cut out like I'm only giving it 1/8th throttle maybe. By the time the engine is warm, it's not intermittant at all--it's a gutless pig.

Anyone have any ideas?

Thanks,
Mike

 

[HBarlow]

When the APPS fails it is as if the accelerator pedal is only intermittently connected or suddenly disconnected from the engine. The engine igores your foot on the pedal.

I replaced five or six of them on my '01 in 325k miles. Several of them simply failed suddenly and completely without prior symptom. One or two others would quit but could be temporarily restored by "exercising the pedal" ie repeated repetitions of pressing rapidly to the floor and release. This allowed me to limp it into town once or twice.

Your description doesn't sound like an APPS problem.

 

[DavidC]

Start with the easy stuff and disconnect the comp and put it back to stock. This does not mean simply turning it off. You need to disconnect everything except the hot and ground.



Dave

 

[Midnite]

Okay, I finally got a chance to disconnect the MAP and data link connectors and return them to the stock config. Unfortunately same problem, although I can definitely tell the absence of the comp (less timing advance knock, slightly less responsive). The check engine light is still lit, and there are no new codes--only P1693.

I hooked the comp back up for now. I'm thinking my next step will be to borrow a Smarty and try to read all the codes since the key trick may not show them all. I may also try to hook up someone else's comp in place of mine to see if it acts differently.

Any other ideas or suggestions?

Thanks,
Mike

 

[DavidC]

I take it you have replaced the fuel filter and the Fass is putting out good pressure. Other than that I am not sure about trouble shooting past that to find out if it is VP44 related, ECM, sensor etc. Sounds fuel related tho. Maybe the bypass valve on the VP stuck open and returning to the tank. The bypass is suppose to open at 14psi and allow excess to go to the tank. Thats all the thoughts I have for now.



Dave

 

[Midnite]

I changed the fuel filter about mid-winter when I gelled up, but honestly it doesn't seem like a fuel problem at all to me. Every fuel problem I've had, the truck either wouldn't run at all, or it would chug and sputter, and it's not displaying either of those behaviors.

I do have good fuel pressure--a rock solid 16 psi. I do have a steady trickle going back to the tank, but I've always had that since I installed the FASS.

I want to see what companion code(s) got set (which triggered P1693), and I'm thinking that'll probably tell me what the story is.

Thanks for the ideas,
Mike

 

[Midnite]

Well, it looks like I need to replace my MAP sensor. There was only one other code set, and it was P0107, "MAP sensor voltage too low". I think the fact that it acted normally when cold is simply due to the nature of the internal failure of the sensor, whatever that might be.

The local Cummins shop was closed, so I ordered one from hoeslidiesel.com.

Thanks to JR2 for the use of his Smarty--without reading the codes I'd be totally in the dark. Dave and Harvey, thanks for your help.

Mike