Can the APPS set screws be adjusted?

[GWS]

I know, the shop manual says not to touch them, as this will destroy the electronic calibration, but it seems to me I remember someone talking about adjusting them to increase or decrease the amount of low boost fueling. I'm still trying to work through this problem of excessive low boost smoke that I never had before. Air filter looks fine, plus I have no trouble getting plenty of boost. There is no oil leaking into the intercooler from the turbo. I still have to check the fuel return valve to make sure its working properly. Performance seems great except for the large plume of smoke at low boost. Anyone with experience monkeying with the APPS set screws?

 

[Jack in Alaska]

APPS tinkering

I recently had my APPS replaced due to a "runaway engine" condition. So far it has solved the problem.

The DC service manager said that he did try to adjust an APPS once and it was definitly the wrong thing to do. He said it took him over 3 hrs. to finally get the truck to even run let alone getting it correct. He advised me to NEVER mess with those screws. The warning is there for a reason. He convinced me.

 

[GWS]

Thanks Jack. That's all I need to know!

 

[JR2]

What exactly do you mean by excessive low boost smoke? I have almost the same setup as you and I get a fairly decent sized smoke cloud when I hammer it.

The one thing I might try is to clean or replace your IAT sensor. I cleaned my Dad's (Jack in Alaska) and his mileage seems to be going up. I replaced mine and my cloud of smoke at low boost got smaller.

 

[Todd T]

it can be done but as he said its very tricky,



the point of doing it, is to fine tune the APPS to be right on the threshold of an "off idle voltage" at idle. that way as soon as you look at the throttle wrong, it will know you have moved it and start following its algarithums. it has to be done with a volt meter installed and is tricky to set. it will move on you, as you tighten the bolts back up. the best bet is to not mess with it unless you have to time to get it right. especially with you having an auto. it could affect shift points if not set right.

 

[GWS]

JR2 and Todd, thanks for your replys. When folks used to report black smoke at low boost I could say that I really had little or none unless the throttle was floored from a standstill. Now however I have to be careful around town so I don't choke some poor motorist behind me. If I go easy up to 10 lbs boost it's stays pretty clean, but if I'm the least bit aggressive, I will produce a black cloud that can be seen in the rear view mirror. This excess smoke occurs even with the VA disconnected and the Edge turned off. Maybe an injector has gone bad, but I doubt it since the service manual says a DTC would be set, and besides, the performance is very good. The re-0880 looks ok but I will clean it anyway and see if that helps. I will also clean the IAT sensor. I did get a MAP sensor DTC a while ago but it has not returned, and the code was for a low voltage, not high. The manual says black smoke can occur if the fuel return line is restricted, so I will check the overflow valve on the pump. Changed the fuel filter yesterday with no results. Getting up to 42 lbs boost. For some reason the amount of fueling has increased, especially at low boost.

 

[JR2]

Now I understad what you mean my excessive black smoke. Are you telling us that you can get 40+ lbs of boost with out the PE or VA on? I would say that something is wrong if that is the case. I think it might be time to take the old girl to the dealer (or since it is a 98. 5 and your warranty is over) to Cummins and let them try to fix it.

 

[GWS]

Hey JR2. No, this level of boost is achieved with 275's plus VA plus the Edge in any level (1,2 or 3). With the Edge off, max boost is approx 30-35. I may be kidding myself, but it seems to me the situation is improving ever so slightly. Initially, the big bad black belch was associated with an engine stumble. The stumble has disappeared and the smoke seems (I think) to be diminishing slightly. A while ago, while travelling from Toronto to Wawa I purchased some cheap diesel at a fuel station that was usually closed. When I noticed the smoke/stumbe back at home, I added approx. 1/2 tank to dilute this fuel. I expected immediate results, but perhaps it will take a tank or two for anything bad in the fuel to burn out of the system. I'm not saying this is the cause, but rather one theory of many.