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

[Gary - K7GLD]

Sorry for the length of these opening posts - this is a condensation of a MUCH larger original thread on the same subject.



4 years ago, due to their high and premature failure rate, I started a TDR thread on the 2nd generation APPS, entitled "Anatomy of an APPS". That thread ran MANY pages, with hundreds of viewers and posts. After lots of intense discussion and a few dead-ends looking for solutions towards improving on the "Fly-by-wire" engine throttle DC gave us, we finally arrived at some excellent, working and CHEAPER alternatives to what formerly was available to us.



Why be concerned about the APPS, and the apparently high rate of premature failures? Well, they aren't cheap - nearly $500 plus installation, and at about half the cost of a VP-44 injection pump, are certainly WORTH a bit of concern and attention!



This thread discusses and describes what was developed, and eliminates the need for readers to wade thru over 12 web pages and 400+ posts of the original thread.

LEGAL DISCLAIMER:



EVERYTHING pictured and described below is PURELY for information, and IS NOT a recommendation that ANYONE do as is shown here - and if some DO choose to copy any part of what is seen here, they do so at their own risk!

OK, now down to business!



The APPS on our trucks is mounted on THIS bracket, on the driver's side of the engine:



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Here's the back side, where the actual APPS module is mounted:



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Once removed, and opened up, the inside of the APPS module looks like THIS:



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The above is the electronics side, showing the Idle Validation Switch (IVS) section - here's the other side, showing the rotary potentiometer that actually signals the ECM when the accelerator pedal is depressed - you will note the resistance traces in the printed circuit backing, and on the removed part to the left, the rotary contact fingers that actually make contact with the traces:



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That potentiometer is NO DIFFERENT in construction than a common volume control as used on many radios and stereo amplifiers! In fact, what you are seeing on BOTH sides of the APPS circuitry is NOT a solid plated board, but rather, a thin Mylar membrane - like a sheet of photo film - that is plated with printed circuitry, to which the individual electronics components are surface mounted - the potentiometer traces are similarly an applied thin resistance track, then both sides are simply GLUED to a support backing. In my opinion, a POOR and flimsy method of construction, especially for the purpose it's used for, and PRICE this one demands! Far more like a dime-store kid's toy than a several hundred dollar automotive part!



(MORE BELOW!)

 

[Gary - K7GLD]

For a long time, we were mystified as to exactly HOW the APPS functioned, and what the exact function was for the electronics inside. One TDR member finally drew up a schematic of the electronics section, deciphered the various components into functions, and determined that ALL that section did, was operate as a common Single Pole Double Throw (SPDT) switch! In other words, a simple, cheap, and common manual switch could replace all that electronics circuitry!



Here, for reference, and for those familiar with electronics schematics, is the one for the APPS:



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And the electrical equivalent of the complex IVS circuit shown as a simple switch, on the lower part of the drawing, as well as the potentiometer section at the top - note the pin connection numbers - these are clearly molded into the connector pin area of the APPS, and quite easy to see and identify:



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In the beginning, it was thought (by me, at least) that premature APPS failures was due to failure in the potentiometer section - but as time passed, and "failed" APPS modules were checked, virtually EVERY ONE of the half dozen I personally had, checked out perfect in the potentiometer section - and it APPEARS that the actual cause of failure was either in the IVS side, or else the connection used between the thin Mylar printed circuit and the external pins in the connector - that connection when disassembled, looks like THIS:



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As can be seen, there are a total of 6 connections (3 for the potentiometer, and 3 for the IVS), and there is NO solid, direct connection between the internal APPS components and the pin connectors, instead, the APPS relies upon a common (and CHEAP!) pressure type conductive contact strip pad seen at the top of the photo - if/when that contact fails or become intermittent, the APPS becomes WORTHLESS, and usually starts causing erratic vehicle accelerator control, and error codes to be displayed to the driver! Adding to the confusion, is the fact that the symptoms of a failing APPS are often mistaken for a failing VP-44!



The only function of the IVS section, is to electronically switch, and signal the ECM when the accelerator goes from the resting idle position, to the off-idle position, and then back again when the throttle returns to idle position. Pretty elaborate and complicated circuit for so simple a function!



Armed with this latest development as to specifics of APPS function, several of us pitched in to come up with substitute devices and methods to replace the OEM APPS with better and/or cheaper substitutes. It appeared that we needed two primary components, a potentiometer of some sort in the 2K-3K resistance range for the accelerator function, and a durable and reliable switch for the IVS function.



For this thread, I'll display the 2 "solutions" I have devised and used so far. My first, and currently operating on my truck, looks like this:



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That's the lower side of the front showing the installation of a micro switch (MS) for the IVS function - that's a sealed, 10-million operations rated switch, and sells for about $8. 50 from Mouser Electronics.



Here's the upper side:



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A breakdown shot of the potentiometer linkage that operates off the APPS bracket belcrank, also showing the potentiometer and brackets early in development - minor changes/additions were made in the finished assembly:



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That was shot prior to final wiring, and shows a common in-line slide-type, cheapie potentiometer also bought thru Mouser - for about $2, along with the actuating arm I fabricated to connect from the APPS belcrank to the potentiometer control lever - the spring seen is to maintain constant tension on the assembly - no slop at all!



Since the potentiometer shown is only 2000 ohms end-to-end, and the ECM works best with one in the 2K-3K range, a 470 ohm fixed resistor was added at the WOT end of the pot (as can be seen mounted to the mounting strip in the pic below) - not a problem, since that well matches what the OEM pot provides, and which uses only about 1600 ohms or so of actual potentiometer wiper travel in normal operation.





Here it is installed and working perfectly on my truck:



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The above setup totaled about $15 in cost, and is currently under extended testing in my truck, with absolutely NO problems so far - it worked perfectly from the moment it was installed! I wanted to try a relatively cheap potentiometer in this version, to see what sort of lifespan it would deliver in this service - after all, even if it only lasted a year or 2, at $2, it's quick, easy and CHEAP to replace! There ARE other, more expensive and durable ones easily available as well, for those wanting longer lifespan. Truth is, judging only by appearance, the $2 potentiometer I've used LOOKS to be better in quality and construction than the one used in the DC APPS!



(MORE BELOW!)

 

[Gary - K7GLD]

There's absolutely NOTHING mounted on the backside of the bracket, the OEM APPS module was removed and abandoned! I cut off and used the 6-pin OEM APPS plug seen earlier, after soldering short connecting leads to the stubs of the pins protruding thru the rear side of that cut off plug - aftermarket plugs that can be used sell from about $8 to $15, depending on whether steel or gold pin versions are used - the DC OEM plug pins are gold, and I also have some aftermarket plugs to be used on other versions I'm playing with that use gold pins and sockets.



The resistors and disc capacitors seen mounted on the mounting strip are used as a spike/noise filter to keep electrical garbage from the switch contacts from feeding back into the ECM - might not be needed, but I'm a Ham Radio operator, and use a high-power mobile setup in my truck, and take extra effort to keep radiated RF energy out of my sensitive truck computer wiring - besides, it only costs pennies from Radio Shack - here's the simple schematic for it:



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OKAyyyyy - so that's finished, and working great so far - but as some have already noticed, the components I have used, and where I have them placed on my manual 6-speed truck APPS bracket, interferes with the added APPS bracket linkage as used on the automatic transmission trucks - so what can be done for THEM?



Well, as an alternative, and working on the assumption that most members here either have a perfectly functional APPS module, or a "failed" one that quite possibly has a fully functional potentiometer section, I worked this IVS module and bracket up, along with the spike/noise filter, as a single-piece module using another MS, for simplicity and ease of construction and installation - plus compactness:



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In this setup, either the OEM DC APPS remains on the rear side of the plate as it originally did, or else use an otherwise IVS-failed one, and ONLY the potentiometer section - 3 of the 6 pins - is used, and the micro switch is used for the IVS function - the remaining 3 pins.



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So why would any SANE owner deliberately modify or mess with a WORKING APPS setup? Well, I am convinced the general construction of the OEM APPS is cheap in design and materials, and basically a failure just waiting to happen! I'd far rather modify it with a component that is purely mechanical, and of a design and construction that affords better reliability, is easily replaced - and very LOW in cost - the MS setup seen here appears to provide all that.



Added to that, is the fact that using the method described and pictured here, the full OEM operation and function can easily and quickly be returned to, simply by switching plugs, and, this setup is fully compatible with either auto transmissions or manual. The cost of this setup is easy to take as well - an $8 MS, and about $25 for the plugs used in the short adapter harness - plus a few pennies for miscellaneous bits and pieces.



Other TDR members have successfully developed working setups using another APPS module that is a DIRECT substitute for the OEM DC APPS module - these alternative modules sell for well under $100 for the version that has only the potentiometer section, and others in the $120 range for ones WITH the electronic IVS section - one of those versions is currently available as a relatively "Plug-and play" kit for about $140 - far cheaper than what DC charges for theirs!



Here's a pic of that option - this approach is complete as seen - the internal IVS section is used, just as it is in the DC OEM APPS, but THIS alternative is FAR cheaper than DC's:



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Timbo can be contacted directly for his version seen above at:



-- email address removed --



SO, this is still a work in progress - we have the basics pretty well ironed out, and several different types and versions out on the road, under test and racking up miles - there is enough info here for some owners to do their own testing, and at least one relatively inexpensive alternate substitute APPS available so far...



ENJOY!

 

[Gary - K7GLD]

Here's a Mouser parts # breakdown of the parts I have used, and displayed above:



Mouser Electronics - Electronic Component Distributor



The in-line slide potentiometer:



Part # 312-9302F-2K Price - $2. 12



The Micro switch:



Part # 653-02VW-5L2A-!MS - $8. 33



The small spike/noise filter components and mounting strip are common Radio Shack items, and run about $5 total cost



The extender harness plug ends, with gold pins, are available here:



Batts Racing is your Deutsch Connector source



And here's the plugs displayed, with pricing - I used the Gold pin, 16 ga. Variety:



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Of course, misc. small parts, wire and such add to the total - plus a bit of sweat and swearing!



Keep in mind the potentiometer shown is a cheapie - more durable and more expensive ones ARE available - I just wanted to see how this particular type would hold up.



I'll leave it to developers of the other setups, if they choose to pop in here, to post their own info and parts lists.

 

[benhall]

Looks like a good set up. I just had to replace mine on Thursday, the day before starting a 1000 mile drive. I still have the one I replaced, so doing something like this is an option now. Too bad I'm not electronically inclined enough to do this.

Ben

 

[BradPatterson]

I got the new Williams apps installed tonight that I received from member Timbo. My camera batteries died after only one photo..... (sorry Tim). As you can see in the photo this is truely a bolt on, plug and play, factory looking piece! (the new Williams apps with new plug is on the top)I received a complete easy to follow instruction sheet with the new apps. Anyone who has adjusted or changed out one of these knows how simple of an install this is and if you have never done one don't worry the instructions walk you through it step by step. After the install setting the voltage is a piece of cake using the idle stop screw. Started right up, no codes or issues of any kind. If anyone is looking for a "plug in" replacement for the DC app$$$ check this one out! Thanks Tim... ... ... ... ..... Brad

 

[Gary - K7GLD]

Looks like we have a WINNER! Oo.

 

[benhall]

Dumb question, but how do you set the voltage on this?

 

[BradPatterson]

voltage adjustment

Ben ,you use the idle stop screw on the bell crank assembly. I think ALL you fellers that share your knowledge on these forums are winners! I can find answers to most of the questions I have using the search... ..... thanks... ... Brad ( ooops . . did you mean voltage on this one or the DC one?)

 

[Vaughn MacKenzie]

Great work Gary! (and Timbo too )

This inspires me to do something similar with the TPS on my 12V automatic. The issue here is lockup happening too soon in OD which can be corrected by changing the range of the potentiometer & fooling the PCM into thinking more throttle is being dialed up that there actually is. The TPS on the 12V is pretty chintzy too.

Gary another upgrade to your project you may consider is an optic sensor in place of your cherry switch. These are pretty durable/reliable & don't produce noise upon contact like mechanical switches do. Could easily use edge of your bellcrank to block the LED. But nothing wrong with your setup

On your idle val switch, is it NO or NC? If it fails (contacts don't close) would it be stuck at the Idle position, or never see Idle? Maybe the dead pedal failure on the APPS is because the ECM is logically seeing Idle only?

 

[HBarlow]

Great research and design, Gary. I would have happily paid good money for one of your shop-built APPS modules when I was transporting RVs with the '01 Ram I owned previously.



In 325,000 miles of service I replaced the APPS module approximately every 60,000 miles. I learned to carry a MOPAR spare and could replace them in about fifteen minutes but at $400+/copy they weren't cheap.



You should market your product.

 

[Misenheimer]

Is Timbo going to be overwhelmed with orders?? I would like to have one.



Great work Gary WHen I have time I want to construct one like yours.

 

[Gary - K7GLD]

Great work Gary! (and Timbo too )



This inspires me to do something similar with the TPS on my 12V automatic. The issue here is lockup happening too soon in OD which can be corrected by changing the range of the potentiometer & fooling the PCM into thinking more throttle is being dialed up that there actually is. The TPS on the 12V is pretty chintzy too.



Gary another upgrade to your project you may consider is an optic sensor in place of your cherry switch. These are pretty durable/reliable & don't produce noise upon contact like mechanical switches do. Could easily use edge of your bellcrank to block the LED. But nothing wrong with your setup



On your idle val switch, is it NO or NC? If it fails (contacts don't close) would it be stuck at the Idle position, or never see Idle? Maybe the dead pedal failure on the APPS is because the ECM is logically seeing Idle only?

Actually, I *have* a pair of optical shutter wheels and sensors in my drawer, was thinking more along the lines of a resistance stepper to replace the potentiometer, but the IVS switch version would work too. Too bad DC didn't use something like that - not too expensive, and far more reliable.



The MS is connected in a Normally Closed (NC) configuration, which closes the Idle side line, then switches to open as the belcrank rotates, opening the idle side and closing the off-idle line. Just exactly as the OEM IVS section does - but mechanically instead of electronically.



One issue in using solid state electronics in engine controls, is HEAT - especially heat soak in hot weather right after the engine shuts down. These surface-mount solid state components are not actually manually soldered in position, but are sorta "floated" in position and then a small direct flow of heated air from a small gun or oven at the contact areas melts the small film of solder on both the component and the printed circuit trace, bonding them together.



That solder used, has a relatively LOW melting point, to allow the bonding to take place WITHOUT damaging the component or the trace material - so GUESS what happens to those assemblies when underhood temps get up over 200 degrees and more...



The usual redline in temps for solid state assemblies and components is about 160 degrees - WAY lower than common underhood temps at engine shutdown on hot summer days.



This same sensitivity to heat, and construction method, is also used in the small circuit boards used inside our VP-44 injection pumps - do ya suppose that's why THEY were failure prone as well?



Bosch must have, because they made significant changes in the construction of those boards, and the VP-44 as now produced by rebuilders is FAR more reliable than the originals. That's also why some of us have installed timer-controlled blowers to direct outside ducted air over the VP-44 - and in some installations, the APPS as well...



Small Marine bilge blowers are LOTS cheaper than VP-44's!

 

[ed9824v]

put me down for one too. Have yet to have a problem with my new to me 24v gen II. But For a decent price would have one on hand if it ever gets to that point. Even though the write up is great and enough info for me to put one together ED

 

[csutton7]

Moderators---this needs to be pinned, sticky'd or whatever it takes to get it into the hall of fame of fixes for our trucks---thanks to all who participated in getting this accomplished--

Gary-K7gld--I applaud you for your persistience in this--I know this has been a burr in your side for many yrs and it's come to pass that there's now a fix for that crappy part due to your not giving up and getting help along the way----absolutely one of the best fixes for our trucks---chris

 

[Highfinance97]

You should market your product.

Gary and Timbo
Standard does not make one, so maybe you should write them

Standard Motor Products, Inc. >> Home


Great Info. You men deserve a big applause from everyoneOo.

Michael

 

[Gary - K7GLD]

Moderators---this needs to be pinned, sticky'd or whatever it takes to get it into the hall of fame of fixes for our trucks---thanks to all who participated in getting this accomplished--



Gary-K7gld--I applaud you for your persistience in this--I know this has been a burr in your side for many yrs and it's come to pass that there's now a fix for that crappy part due to your not giving up and getting help along the way----absolutely one of the best fixes for our trucks---chris

Thanks for the bouquet Chris - and ALWAYS good to hear from you - but truth is, all this was very much a GROUP EFFORT, and perhaps the single largest breakthru, was when KarlC took the time and effort to actually draw out a schematic of the APPS, listed components and functions - and discovered that ALL the IVS was doing, was performing as a simple SPDT switch!



Once that was figured out, the rest all sorta snowballed from there to where we are today!



Roses? YOU BET - to each and every one in this project who contributed, stuck with it, and pulled $$$ out of their own pockets on pure speculation that something positive WOULD come from the $$$ and effort - it HAS, and...

THANKS A MILLION GUYS!​

 

[timbo]

I just wanted to THANK all of you for your APPLAUSE Gary is right though, this was definitely a GROUP EFFORT!!!! THANK YOU TO EVERYONE INVOLVED!!!

 

[rweis]

For those wanting to do the micro switch (ie get rid of some more electronic circuitry) for the IVS (idle validation switch) or want to read the whole foundation of this sequel, we are still tweaking over in https://www.turbodieselregister.com...nsmission-1998-5-2002/99611-anatomy-apps.html.



Bob Weis

 

[SHobbs]

Whats the possiblity of some kind of kit with instructions to do a retro fit? Keep it tucked away for that future failure of the APPS. This is something I would like to do if I had the parts and info to do it.



My hat is off to you for the work and time you have put into this project. Incredible job.