Engine/Transmission (1998.5 - 2002) Anatomy of an APPS

[Gary - K7GLD]

Any chance something like this could used in place of the APPS:

"Smart" sensor targets heavy-duty applications. (American

This seems to be the big killer spec of solid state control devices in high temperature operating environments:

This I. C. has EEProm circuitry with an operating temperature range of -40 [degrees] C to 150 [degrees] C

The underhood areas of our truck can easily GREATLY exceed 150 degrees in summer weather after the engine is shut down (heat soak).



NOW, if a suitable mounting location for the device you have pointed to - or even the existing APPS - could be located INSIDE the cab of the truck away from engine heat, these solid state sensors would stand a lot better chance of survival.



And one that doesn't rely upon actual sliding contact of internal components as our APPS units do (and what the above pointer covers) would also be a big plus.

 

[mhenon]

I also ran across this peddle/TPS from Cummins but it probably costs a fortune too: http://www.abc-companies.com/servic...elerator pedal - Throttle Position Sensor.pdf

I'm kinda surprised one of the after-market guy's (Vulcan, Glacier etc. ) hasn't taken on the task of a new improved TPS(hint!).

Anyway, the APPS is acting up and a new one is on the way. It did last almost 100K miles but at $400 bucks at whack...

Mike

 

[mhenon]

... NOW, if a suitable mounting location for the device you have pointed to - or even the existing APPS - could be located INSIDE the cab of the truck away from engine heat, these solid state sensors would stand a lot better chance of survival...

Maybe that's the answer. Couldn't the exsisting control cable be shortened and the whole assembly mounted under the dash somewhere? Or keep the thing as is and move it away from the engine like we did with the LP.

Just thinking out loud here but there must be a way to improve reliability if not replace it altogether.

Mike

 

[Gary - K7GLD]

Maybe that's the answer. Couldn't the exsisting control cable be shortened and the whole assembly mounted under the dash somewhere? Or keep the thing as is and move it away from the engine like we did with the LP.

Just thinking out loud here but there must be a way to improve reliability if not replace it altogether.

Mike

WELL, there's certainly no reason the APPS *has* to be located right at the engine where it is now located. I have a complete used spare APPS and it's mounting plate - I'll have to take a look at it and the OEM throttle linkage setup to see what might be needed to fabricate new mounts and linkage, and get it somewhere inside and up a bit under the dashboard on the firewall...

 

[rweis]

When I built the blower for the VP44 for cooling during engine run & 1 1/2 hours after shutdown, the way I attached the blower ducting, it blows OAT air up into the TPS assembly fairly significantly. IF heat to the TPS is - the / part of the - problem it might be worked the same way we cool the VP44.



I would bet it is a combination of TPS environment, repetition, and lack of substancial construction of the TPS and maybe cooling as part of the issue. I only have 88k so I am a long way from finding out if cooling has any effect.



I certainly like the concept of getting the TPS inside the cab away from the engine heat / vibration etc. or a different design that has better construction.



I do not ever remember replacing the TPS on a passenger car / van, has anyone regularly replaced the TPS on other vehicles? I typically run vehicles 250k before replacing them. Why is this a problem to the DC diesel trucks? What is different here from a car / van? other than diesel engine?



Bob Weis

 

[mhenon]

I'm going to look up the price of that peddle/TPS assembly:

http://www.abc-companies.com/servic...elerator pedal - Throttle Position Sensor.pdf

The schematic is identical to the APPS and the TPS part can be replaced seperately. The more I look at that unit the better I like it.

Anyone have a good web-site for used Coach/RV parts?

Mike

 

[rweis]

Doesn't the TPS also actuate the TV cable for the automatic transmission? Something to think about for the auto transmission guys.



Bob Weis



I like the concept, a little goosey about working with the engine aceleration / deceleration systems, but I'm sure I'll get over it. I like the reference to the Cummins ... ,ISB, ... so the probability of a good match is at least reasonably high.

 

[Gary - K7GLD]

I do not ever remember replacing the TPS on a passenger car / van, has anyone regularly replaced the TPS on other vehicles? I typically run vehicles 250k before replacing them. Why is this a problem to the DC diesel trucks? What is different here from a car / van? other than diesel engine?

I believe earlier TPS setups only placed the variable resistor portion of the system close to the engine, and those aren't nearly as temperature sensitive as the other solid state items that are now also incorporated in the APPS as used on our trucks. It's also possible that before the APPS devices got crowded with additional circuitry, larger and more robust potentiometers could be used, and lived longer. For sure, the internal construction of our APPS is PURE TRASH! :{



Good point on the A/T transmission setups and the APPS linkage - might make relocating the APPS more difficult, so will keep that in mind if I fool with mine, and see if only the APPS portion can be split off and relocated, leaving the current linkage and bracketry in place...

When I built the blower for the VP44 for cooling during engine run & 1 1/2 hours after shutdown, the way I attached the blower ducting, it blows OAT air up into the TPS assembly fairly significantly. IF heat to the TPS is - the / part of the - problem it might be worked the same way we cool the VP44.

YUP - same here:



#ad




And actually, I detect a pretty decent cooling airflow around various points of the APPS - which is present both while driving, and for about an hour after the engine is shut down.

 

[gtwitch]

APPS anticipation to failure!!!

I have had my 99 5 spd exhibit the dying APPS syndrome 3 times now on the road and I have been lucky that it restarts and has continued to run, however in anticipation of this failure I stopped at a Cummins Dist in both Salt Lake, UT and Rock Springs, WY yesterday and both did not have this sensor by Cummins #3970085 but could get it. The only place I have found (in this thread) to buy one is Hoesli Diesel. Does anyone out there have any other sources?? As far as I can find there are no Aftermarket sensors.



gtwitch in Wyoming

 

[PRout]

I've been stocking up on new sensors in advance to have them on hand ready for R&R, and for the cost savings vs dealer cost. Hoesli Diesel has been a good source. They ship quickly and the parts come in original Cummins packaging.

One Good Note: Everytime I've lost an APPS they have never left me stranded at least. Not sure about others, but they get more annoying than anything. Yes it could be a safety hazard though.

Good luck!

Time to go outside replace my failed Map Sensor now. . :-laf

 

[mhenon]

... As far as I can find there are no Aftermarket sensors.

gtwitch in Wyoming

I'm AMAZED there are no aftermaket solutions to this problem. I would also be amazed if there were no other sensor that would work in place of the OEM sensor. There whole thing wouldn't be that bad if you could simply buy the TPS and not the whole bellcrank assembly. That's a rip off!

Mines been acting up and I ordered a replacement from Hoesli. I just did the idle voltage adjustment and will see if that cures the issue. In the mean time I'll be looking for a cheaper replacement sensor or more permenant fix to this.

Mike

 

[mhenon]

You can look at the TPS schematic here:ECM details for 1998-2002 Dodge Ram trucks with 24 Valve Cummins diesel engine

One would think there's a TPS out there (Bus/RV world?) that would work with a Cummins engine and made to fit in the OEM bellcrank assembly.

 

[rweis]

I'm going up to ABC Bus in Orlando this week to take a look at Mike's (mhenon) idea (post #82).



Bob Weis



I have never seen measured data of the TPS like end to end resistance readings, angle of arc travel, etc and I think we are going to need some of that data so when we start comparing what we find vs what we have we will have some feel for the compatiability. If someone has a TPS they can gather some data from a spare TPS I think that would be very helpful to have.

 

[Gary - K7GLD]

WELL, I have a complete spare APPS and mounting bracket setup - I'll see what straight-line, and arc of rotation numbers I can provide...



What I'd like to see, are any external resistance measurement specs that might give a clue as to internal condition...

 

[mhenon]

WELL, I have a complete spare APPS and mounting bracket setup - I'll see what straight-line, and arc of rotation numbers I can provide...



What I'd like to see, are any external resistance measurement specs that might give a clue as to internal condition...

Gary, Did you happen to read the adjustment/trouble-shooting section in that Accelorator/TPS link:http://www.abc-companies.com/servic...elerator pedal - Throttle Position Sensor.pdf.

They gave a pretty good run-down on testing their TPS and initial adjustment of a newly installed unit. There was also a final calibration of the TPS calling for "with ingnition "On" depress accelerator fully from idle to full throttle". Sound familiar?

Anyway, while this might not be the exact proceedure to check our APPS I'll bet we could check a few good (new) ones and a few known bad ones and come up with a set of guidelines to help the do-it-yourselfer.

I'll have a new APPS soon. I'll see if anything in the link above makes sense with our APPS.

Mike

 

[mhenon]

Also found this which looks like it came from a service dept. manual:Code P2121 and Dead Pedal - Help [Archive] - Dodge Diesel - Diesel Truck Resource Forums

 

[rweis]

Notice the number of times that the concept of "APP VOLTS DO NOT AGREE WITH IDLE VALIDATION SIGNAL"?



Set Condition: IVS indicates idle while APPS signal voltage indicates not at idle condition or IVS indicates not at idle while APPS signal voltage indicates idle condition. Or, the ECM detected a conformance error between PPS 1 and PPS 2.



I think the idle validation signal is something like the pedal at idle mechanically closes some contacts that tells the ECM "the pedal is at idle mechanically".



I do not have the schematic at work, but I think there are 2 of the IVS's as a redundancy. I could be mistaken here.



Does this imply that the APPS procedure to make sure the apps resistance tag and the resistance at PCM pin ?? are the same (the procedure where you loosen the APPS and adjust it in rotation until the PCM value is as close to the tag number on the APPS as you can).



Is that really more critical than maybe we have given it credit to be? Should that procedure be done yearly? to keep the APPS aligned to what it should be?



Bob Weis

 

[Gary - K7GLD]

As far as I can see, having totally disassembled an APPS, there is NO end-of-travel sensor - on either end of rotation. It appears that the entire operational sensing is done purely by the resistance/voltage presented as the potentiometer fingers travel along their track.



Once initial static settings are done with a new APPS as specified in order to obtain base alignment, and the APPS actually installed, then the active in-vehicle calibration is performed to "introduce" the APPS to the computer, and the idle/WOT positions established for operational reference.



Virtually EVERY one of the several failed APPS units I have seem to perform and track properly as measured only with a meter - so either the resistance contact failure is more intermittent, or else the actual failure - at least on the units I have - is somewhere else in the APPS internal solid state circuitry.

 

[rweis]

Does it appear that contact cleaner would be of any value? ie CAN a contact cleaner spray be introduced into the finger resistance track area? How sealed is the finger resistance track area? Any cracks in the resistance track might be of the hairline variety and not easily visually seen.



Once you get it appart can it be put back together reliability? Maybe in a different housing? ie could you repair a hairline crack and return it to service?



Let me see if I read your post right, Nothing obvious about a "idle verification" set of contacts? "Maybe the active in-vehicle calibration is performed to "introduce" the APPS to the computer, and the idle/WOT positions established for operational reference. ", then the ECM records those end points as the reference. The APPS resistance / finger track is a single track?, single finger wiper?, it stored where the start point is, it reads where it is right now, it stored where the other end is. The "ends" might not actually be "at" the physical ends of the resistance track, but somewhat less than the physical end so there is some flexability establishing the "APPS learn" mode.



I am probably wrong, but tending to think that periodic recalibration (the ohm reading / matching process) back to where the APPS was initially installed might have something to do with it all. Something like the initial resistance value is stored, then the pedal travel resistance is stored at each end, then the ECM takes those two end points and initial point to do its calculations if the APPS is within tolerance.



This is intently interesting if we can solve this one,



Bob Weis

 

[Gary - K7GLD]

I seriously doubt that there's any significant value in disassembling the APPS to clean the resistance tracks - simply drilling the case as I have indicated, and applying a good dose of contact cleaner is about the most practical "FIX" I can see.



And THAT is only IF the problem/failure point IS in the resistance section - there are plenty of other electronic parts inside there that can as easily fail. And as suggested earlier, the APPS is undoubtedly every bit as adversely affected by underhood heat as are other solid state devices.



BUT, as may be visible in the lead photos in this thread, the actual internal circuits, including the resistance tracks, are all mounted onto a thin flexible Mylar type membrane, and THAT in turn is simply glued to the internal APPS case area.



In fact, the portion of the Mylar film with the resistance tracks on the example photo I supplied was not even well adhered to the underlying surface, and clearly was lifted up about 1/16 of an inch at one end of the tracks. Would seem to potentially cause reliability problems as far as constant contact between the tracks and fingers is concerned!



Quite possibly the best mod, if an actual circuit diagram of the APPS could be produced, would be to build a separate electronics board for the APPS, and remotely locate it inside the cab - and then have ONLY the potentiometer(s) remain at the OEM location. IF we had a schematic, that would be relatively easy to accomplish.