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

[rweis]

Ok, the TPS is the next project on the list.



To get good measurements I see 6 pins to do something with.



My test plan is to measure the OEM TPS first, then swap the TPS to the bus TPS and measure that and compare the two.



First do the measurements with the engine not running, but the ignition wire hot to make sure the voltages supplied are supplied.



I see 3 things to measure simultaneously:



First series will be with the OEM TPS for the baseline readings



1. TPS signal level 2. IVS 1 idle active voltage 3. IVS 2 throttle active voltage.

2. Some how try to figure degree of rotation (depression of pedal) at each reading.



Second series will be with the bus TPS for the baseline readings



1. Same as above

2. Same as above



Then see how different the readings are. Mike implied that he mounted the bus TPS and started the engine, but could not advance the rpm as if the throttle active voltage did not match the OEM readings, or the idle active voltage did not ?????.



Any discussion on the process or procedures is welcome until next saturday morning (2 february) test day.



Bob Weis

 

[KarlC]

Hi All,



I was able to draw a rough schematic of the APPS this weekend from Gary's photos. It's pretty rough and some of it doesn't make sense yet. To help out, a list member is sending me a dead APPS to dissect. Hopefully next weekend I'll know more of how it all works.



I thought of something else we can do with this... There should be a way to make a circuit to provide high idle with adjustable RPM using up/down pushbuttons on the dash, like the later trucks do using the cruise control buttons. My thinking is that this device would have male and female APPS connectors and electrically go between the APPS and ECM. If the APPS is not at idle, it would pass the APPS signals through to the ECM. If the APPS is at idle, it would allow the operator to increase or decrease the idle speed with the buttons on the dash (by simulating someone pressing on the accelerator).

 

[mhenon]

Bob, Check the voltage at pin#23 on the PCM with the Williams TPS. Mine never made it up to the . 5volt level even at full throttle. The OEM APPS starts at around . 5v and goes to 4volts or so at WOT. So. . I obviously never got it to accelerate. If that's our only hold up "I think" we're gonna wip this thing.

Karl, I'm sure the high idle thing is do-able. My Quadzilla XZT+ has a high idle feature that's probably doing just what you talking about. Let us know what you find out on the circuit board.

Mike

 

[JAlmon]

Couldn't wait any longer; and, I'll park my truck before I buy an APPS from a dealer. I ordered one from O'Rileys today. They said it was the complete assembly and guaranteed it to be correct. $335 + 15 shipping. We'll see

 

[mhenon]

Any Progress?

Ok, the TPS is the next project on the list.



To get good measurements I see 6 pins to do something with.



My test plan is to measure the OEM TPS first, then swap the TPS to the bus TPS and measure that and compare the two.



First do the measurements with the engine not running, but the ignition wire hot to make sure the voltages supplied are supplied.



I see 3 things to measure simultaneously:



First series will be with the OEM TPS for the baseline readings



1. TPS signal level 2. IVS 1 idle active voltage 3. IVS 2 throttle active voltage.

2. Some how try to figure degree of rotation (depression of pedal) at each reading.



Second series will be with the bus TPS for the baseline readings



1. Same as above

2. Same as above



Then see how different the readings are. Mike implied that he mounted the bus TPS and started the engine, but could not advance the rpm as if the throttle active voltage did not match the OEM readings, or the idle active voltage did not ?????.



Any discussion on the process or procedures is welcome until next saturday morning (2 february) test day.



Bob Weis

Well... ... ... . anything to report Bob? I really logged on this morning hoping to see a new post:"THE APPS IS FIXED!!... . THE APPS IS FIXED!!".

How's the Williams TPS looking? Are those aftermarket electrons going to flow through OEM wiring?

Mike

 

[Gary - K7GLD]

DUNNO - glanced over Bob's way earlier this morning, all I could see was sparks and smoke... :-laf:-laf:-laf



Bob's pretty thorough, and this is likely to require a bit of experimentation to get working properly - you can bet when he does arrive, we'll get a good picture of what went on...

 

[mhenon]

DUNNO - glanced over Bob's way earlier this morning, all I could see was sparks and smoke... :-laf:-laf:-laf



Bob's pretty thorough, and this is likely to require a bit of experimentation to get working properly - you can bet when he does arrive, we'll get a good picture of what went on...

Really bummed that we're travelling and I can't take a more active role in this. I have no doubt Bob will tear into the TPS like a pitbull on a sunday paper. Guess I'm getting anxious!

 

[KarlC]

Got a broken APPS in the mail today from TDR member Monkeyman. I did a few checks on it today but I'm going to take it to work on Monday and make some more checks before I open it up to finish the schematic. I also unplugged the working APPS on my truck and made the same measurements as on his. Here's what I found so far:



Overall (end-to-end) resistance of the throttle element was 2379 ohms on his and 2617 on mine. This variation is probably just manufacturing tolerances. Cummins allows 2000 to 3000. With the wiper at idle, the resistance from the wiper to the ground side of the resistance element was 998 ohms on his and 432 on mine. I would expect these to be closer but may be due to the worn-out element in his.



Karl

 

[rweis]

Had a little job computer server crash come up that took precedence for a couple of weeks, sorry for the delay.



Will start getting the data from the OEM APPS this week. Have to build a set of ohm meter cables that will reach from the OEM APPS to the cab so I can gather engine off data and engine on data to see what is going on while driving and get data recorded.



Has anyone ever hooked up to the APPS and read the readings real time? I guess my real question is "exactely WHAT do we really know about the APPS?" other than it fails.



I would think the resistances are all workable. Series if we need more, parallel if we need less, OR totally rebuild the circuit board and put it somewhere else out of the heat and vibration of the engine compartment like the Wilson complete pedal option (but my ETC would have a hard time with the TV cable if the entire pedal was in the cab)



Depending on the Wilson pedal, maybe the solution will be for the ETC guys to get the TV cable into the cab rather than to screw around with OEM APPS mounted where it is, the manual transmission guys would not have that problem.



Bob Weis

 

[mhenon]

Bob, I cut my OEM wiring harness to the APPS to install the Weather Pack connectors. I left about a 4" pigtail on each wire to the OEM 6 pin connector and installed weather packs there too. Now I can switch between OEM APPS to Williams TPS (when we get it working) very easily.

I just mentioned this as once you cut the wires. . it would be a good time to "T" in additional wiring, like we did on pin #23 PCM, for test purposes. I didn't "T" anything in but could simply make a short 6 wire jumper with weather packs on both ends and provide access on the jumper for testing.

Anyway, just throwing some ideas out there. Good luck on the testing.

Mike

 

[KarlC]

APPS Enthusiasts,



I've done some analysis of the APPS, and here's what I found. WARNING -- this is going to be long.



At the bottom is a schematic of the electronics inside an APPS. I had to break it into two parts to fit it in here. The two halves don't seem to match up exactly, but you can easily figure it out as there are only two lines going between the two halves. This APPS was out of an '02 truck and it may be slightly different than other years. It came from TDR member Monkeyman. Many thanks for donating one to the project. The idle calibration voltage marked on it was 0. 620V.



I tested it before opening it up and found the following.



Overall resistance: 2379 ohms

IVS switch point: 0. 812V up

0. 732V down



The IVS switch points are the throttle wiper output voltage when the IVS outputs switch. The reason there are up and down IVS switch points is to avoid it continually switching on and off if the throttle is held at the switch point. This is called hysteresis and is commonly used in electronics to avoid problems at thresholds like this. Both IVS contacts switch simultaneously.



The travel of the bell crank is such that at idle the wipers are approximately 12% of the way up the resistance elements, probably to avoid non-linear characteristics near the end. The full-throttle end probably does this too, but I didn't check.



The electronics are there to emulate the operation of a mechanical IVS switch. As far as I can tell that's all it does.



This APPS has wipers that scrape along the resistance elements and would tend to dig in, as has been discussed before. I didn't notice any damage to the elements, and the throttle voltage had no erratic output throughout its range.



I did come across another point of failure for the APPS. The connections from the circuit board to the 6-pin connector are made through zebra strips. These are often used in electronics to make connections to liquid crystal displays. Have you ever had a digital watch where a segment or two in the display goes out and then will come back if you tap on it? You can probably thank a zebra strip for this. This could be contributing to failures of the APPS.



As far as a replacement for the APPS goes, I think it can be done but not without some work. I'm certain a very important design criterion was to have the IVS circuit be separate and redundant to the throttle circuit. This is an obvious safety item. If the throttle wiper becomes erratic and you let up on the pedal, you really want the truck return to idle. I'm sure this is the primary function of the IVS switch, and the redundancy is important.



With this in mind, I would strongly recommend any replacements using a separate switch for the IVS function. This could be as simple as a mechanical microswitch actuated by the bell crank. It only would switch coming off idle so there is much less wear than on the throttle potentiometer.



Then there is the throttle potentiometer. The Cummins book says it has to be between 2000 and 3000 ohms. I don't know how critical this is but 2500 ohms is a good place to shoot for. What's needed is a position sensor, and there are many types of these. One that could be directly adapted is a string potentiometer, or string pot. These go by various names but the idea is a rotary potentiometer with a pulley on its shaft and a string wound around that. When the string is pulled the potentiometer wiper moves. When released a spring returns it to the original position.



You may laugh, but some of these are very well made, used by NASA and in aircraft flight controls. They use thin stainless cable instead of string. I don't think it would be too hard to adapt one of these to be operated by the bell crank.



Another suggestion I have it to move the APPS inside the cab. I know this is not very feasible for trucks with automatic transmissions but getting it out of the engine environment can't hurt.



I've probably missed some important things, so please ask.



Karl

 

[Gary - K7GLD]

HEY, GREAT JOB on that schematic! Makes great potential for working up a separate component board, remoted out of the engine bay, and leaving only the potentiometer assembly in the current location. As time and inclination permit, I'll start checking availability of the various components.



Thanks from all us APPS experimenters! Oo.



(EDIT)



Do you have any idea as to values of the various capacitors and R5? FL 1-3 must be some form of interference filters - have any clue as to value or type?

 

[KarlC]

Do you have any idea as to values of the various capacitors and R5? FL 1-3 must be some form of interference filters - have any clue as to value or type?

None of the capacitors' values were marked on the parts so I couldn't put them in on the schematic. It's usually tough to measure the value of capacitors while in the circuit so I didn't try, would have to remove them from the board to do it. The values of some of the capacitors are easy to guess from understanding how the circuit works. Others aren't as easy so I'll remove those and measure them.



Here's my guess at the capacitor values I feel confident about:

C6, C8 0. 001uF

C7, C9, C10 0. 1uF



FL1-FL3 are filters like you said. They're labeled 332, possibly meaning 3300pF capacitance but I don't know. I'll see if I can find something out about them.



R5 is zero ohms. Zero-ohm resistors are put in where the layout needs to jump over a trace on the board. Just short it out.



I also don't know what the two transistors are. Probably 2N3904 would work just fine.



Karl

 

[Gary - K7GLD]

Thanks Karl - I've tried joining the 2 schematic halves, and joining the 3. 7 volt lines as I *think* they should connect - I assume they all essentially join at the lower right of the schematic, from the J1-5 (incoming 5 volt line) pin, and after passing thru the several components that drop the 5 volt potential to the labeled 3. 7 volts? My additions are the lines in red...



#ad




For those interested, here's a pic of a section of ECM diagram as provided on a TDR thread related specifically to the ECM. That larger diagram included the various peripheral sensors, IAT, CPS, etc. , including this of the APPS equivalent circuit:

#ad




You can see the APPS pinouts, as well as, on the extreme right, the corresponding ECM pins the APPS connects to. Interesting to note, that this diagram displays a simple switch to perform IVS operation, rather than complicated solid state electronic circuitry...



.​

 

[KarlC]

Gary,

Yes you are correct. All the 3. 7V points do connect together, and are fed from the 5-volt line after going through the two diodes of CR3 plus R15. Your schematic seems to have lost the line going down from C11.

 

[Gary - K7GLD]

Gary,



Yes you are correct. All the 3. 7V points do connect together, and are fed from the 5-volt line after going through the two diodes of CR3 plus R15. Your schematic seems to have lost the line going down from C11.

Thanks Karl - I corrected the schematic up above...

 

[KarlC]

Here are all the capacitor values. Some of these are corrections to what I listed earlier:

C6, C8 25pF

C1, C2, C11, C12 470pF

C4, C5, C7, C9 0. 001µF

C3, C13 0. 01µF

C10 0. 1µF



FL1-FL3 appear to be T-section filters. These are three-terminal devices with two inductors in series and a capacitor from the junction of them to ground. The capacitor is 3300pF. I don't know what value the inductors are because the equipment we have isn't able to measure them.

 

[Gary - K7GLD]

Thanks for the update - and let me see if I understand your earlier supposition that ALL the APPS internal solid state stuff does is ELECTRONICALLY emulate a plain old off/on switch, as triggered by the position/resistance of the potentiometer arm?



IF true, then a simple 2500 (or so) ohm pot could be substituted for the accellerator position function (pins J1-3,4,5), adapted to fit/connect to the OEM APPS bracket - and then, a standard microswitch or similar, properly mounted to be activated by the throttle cable/linkage, would mechanically perform the IVS function (pins J1-1,2,6)- doing away with virtually ALL the electronics?



Seems WAYYyyy too easy! But sure would be nice! Oo.

 

[Gary - K7GLD]

OK, I've updated my version of the above schematic to show all the capacitor values - hope I got them all right! :-laf



NOW, to see where all this next leads us!

 

[KarlC]

Thanks for the update - and let me see if I understand your earlier supposition that ALL the APPS internal solid state stuff does is ELECTRONICALLY emulate a plain old off/on switch, as triggered by the position/resistance of the potentiometer arm?

Yes, all the surface-mount electronics is only there to emulate a plain 'ole SPDT switch.

IF true, then a simple 2500 (or so) ohm pot could be substituted for that function (pins J1-3,4,5), adapted to fit/connect to the OEM bracket - and then, a standard microswitch or similar, properly mounted to be activated by the throttle cable linkage, would mechanically perform the IVS function (pins J1-2,6)- doing away with virtually ALL the electronics?



Seems WAYYyyy too easy! But sure would be nice and easy! Oo.

Yes, I think it would be that easy. The challenge is mostly one of mechanical fit. Don't get just any 'ol pot, though. Running thousands of hours, hundreds of thousands of wiper movements past the operating point at temperature with vibration is nothing to scoff at.



This may have been mentioned before... using the cruise control doesn't put any wear on the APPS.



The APPS probably started out to replace mechanical throttle linkage. As with a lot of design, it probably was phased in gradually and made to accommodate existing stuff. I don't know, but wouldn't be surprised if some school buses were made with an APPS at the pedal and a servo in the back to operate the linkage of a mechanical injection pump.



Some automotive designers are scared $%#*less when it comes to radical changes, so they change one thing at a time. Minimize risk of recall.