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

[Gary - K7GLD]

OK, my plugs arrived today, and I have finished APPS conversion #2



This is my OEM APPS and bracket, removed when I installed conversion #1 - I figure the switch to a mechanical IVS switch is a common-sense move that removes a potentially failure prone and poorly made element from my engine control. However, since the APPS was functioning perfectly before removal, I wanted to be able to quickly and easily return it to OEM form and operation quickly and easily - so made up a simple APPS harness extender so I can switch from modded to unmodded at will. This setup uses ONLY the potentiometer section of the OEM APPS module.



Here again is the front side of the APPS bracket, showing that only the MS is in there, and the rest of that area free for the added linkages and cables used in automatic transmission trucks:



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Dunno when it will be installed - not until I have problems with the version now installed on the truck most likely - and that might be a while...



And on the other side, here's the newly added extender/adapter harness:



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And tidied up:



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Believe me, I made every effort to make sure all wiring was proper, and double and triple checked connections! :-laf

 

[rweis]

Well, time to cleanup some more.



I am running bus APPS pot, MS IVS. 2@ 0121 codes while running around town this afternoon. 0121 gives you a dead pedal.



#1 of the dead pedals recovered itself, #2 I pulled over to the side of the road and it recovered.



Thoughts:



I am runing . 440 volts at idle - may not be enough with the MS.



The bus IVS did not exhibit any 0121 except when doing the install. The bus IVS did not 0121 while driving.



FYI at this point.



Bob Weis

 

[BradPatterson]

Thanks Timbo for the "NEW" apps I received today. I'll get it installed this weekend and post up a few pics and comments on the install. Nice looking piece man. For all you guys that have been working on these my hat is off to ya, great work!!... ... . Brad

 

[Gary - K7GLD]

OK, time to demonstrate my ignorance and lack of understanding again... :-laf



As I see it, the ONLY reason for concern and attention to the initial voltage adjustment at the OEM APPS, is due to component manufacturing tolerance variations in the electronic IVS section - and that is due to the need to calibrate the IVS to activate at it's own unique and specific trigger voltage, and in relation to the APPS throttle potentiometer mechanical idle adjustment.



BUT, if the OEM APPS IVS is NOT being used, as in my case - and those who have also abandoned the electronic IVS section in favor of the purely mechanical MS, what's the purpose or NEED to worry about the threshold voltage to a part of the system that is no longer being used - or even connected?



In my setup, using a plain common stereo-type potentiometer and MS, I didn't pay any attention to any "setting voltage" - and it worked perfectly from the start! I can see that in Timbo's setup - and Bob's, while he was trying to use the electronic IVS section - but why would that be an issue once the electronic IVS is no longer used?



I'm clearly missing something here, at least as far as setups NOT USING an electronic IVS is concerned...

 

[rweis]

There is something more to this than meets the eye.



I'm using the MS IVS and the APPS pot.



The ECM is having some issues about the calibration voltage. I have done the key on, depress slowly, let up slowly, key off thing several times. However when the ECM thinks the calibration voltage has gotten out of range (whatever that is) and throws a 0121 you have zero throttle control as it reverts to an "idle IVS" and takes the engine to idle.



Someone has to know how or where to read this stored voltage value and how to reset it. The reseting of the ECM stored voltage value is very unclear. Maybe disconnecting the batteries for ??? long will do it. 30 minutes is generally what I think I have read as acceptable to clear the ECM APPS voltage.



There is just something else going on. Might have to do with the auto transmission. I do not know, but something.



At 0300 I went to disconnect the positive on both batteries. I also left the key switch in the on position (read that somewhere about leaving the key on with batteries disconnected so any capacitors would be discharged). At 0700 I am going to reconnect the batteries and the first thing I will do is "reset" the APPS pot. Let's see if this has any effect.



Bob Weis

 

[mhenon]

Bob, pull your battery and turn the headlights on. Any caps in the system will be drained in a micro-second. Leaving the cab door open open will do the same as the cab lights will drain the system also. I've had some tough codes that couldn't be cleared using my ScanGauge and this has always worked for me.

Mike

 

[JLandry]

Bob and Gary,



I've been trying to follow your discussions about the APPS and IVS voltage settings and I have questions about your understanding of a few things. Some of this is probably rehashing old stuff and I apologize for it. I'm just trying to keep up to speed on what you guys know...



The functioning of the APPS reostat seems pretty straight forward. Once the ECM learns the full range of the reostat, the voltage it produces tells the ECM how much power the driver wants. Now if I'm not mistaken, the only thing we may not be clear on is the minimum and maximum voltage signal the ECM will tolerate from the APPS before it thinks something is wrong with the APPS reostat and a DTC is set. Am I correct in understanding there's been some conflicting results in some cases where the ECM seems not to care about the APPS minimum (idle) voltage, while in other tests it does?



Also, do we yet know the exact purpose of the IVS?



Obviously when set, the IVS is telling the ECM the APPS is at idle. But doesn't the ECM still start to increase engine rpm as APPS voltage is increased from the idle voltage, even though the IVS is still in the "idle on" state? Or does the ECM not respond to APPS voltage increase until the IVS is triggered? I assume it's the former. If that's the case, then the IVS must serve only as a verification to the ECM that the APPS voltage isn't malfunctioning and running away... right? If this is true, then maybe the ECM has a limit as to how much the APPS voltage can increase from idle before it needs to see the IVS state change to "idle on" or a DTC is set and the ECM reverts the engine to idle for safety.



Can you please clarify your understanding of all this?



BTW, today I hope to measure the voltages on my original OEM APPS while still in my truck, remove it, and then install, calibrate, and test the Williams APPS. I'll let you know how it goes.



Best regards,



John L.

 

[Gary - K7GLD]

John, you see it pretty much the same as I do - I feel that one of the parameters the ECM is looking for, is a potentiometer maximum (end-to-end) resistance of about 2500 ohms - some have said from 2000-3000 ohms will work. All the APPS pots I have tested have been close to 2500 ohms, varying by perhaps 100 ohms from one to another. The actual TRAVEL of the potentiometer wiper is considerably less - only about 1600 ohms in my OEM APPS, and also what I set my own homebrew APPS setup to. As can be seen, the resistance tolerance of the APPS, and what the ECM will recognize is pretty wide and non critical, as long as it's reasonably CLOSE.



And yes, It's my assumption that the "ECM setup" procedure, is to enter into the ECM the maximum low-to-high resistance travel from idle to WOT for the ECM to store as reference. The NEXT needed parameter, is the threshold point, at which the APPS internal (in the case of the OEM APPS) IVS triggers and goes from idle mode, to OFF idle mode.



I personally feel that set point varies slightly from one IVS circuit to another, due to manufacturing tolerances in the individual components used, and the set point needs to be at a point just slightly after the accelerator comes off idle, and then return again just before the throttle returns to idle position.



This coordination of settings with the OEM APPS, typically is done by use of the ability to slightly rotate the OEM APPS in it's mount to obtain the trigger position, and also (if needed) by use of the stop screws on each end post of the belcrank - but actually, I suspect the APPS mount setting is the one most important. And, as an aid to the installing technician, each APPS module is tested after manufacture, and the voltage needed for it to electronically trip, is printed right on the APPS itself!



And as you say, if the IVS trigger setting is too LOW (reference voltage too HIGH) in the potentiometer rotation, the ECM is always looking at what it sees as a triggered, WOT (off idle) condition - and sets a code as soon as the ignition is switched on - and if the trigger setting is too LATE (reference voltage too LOW), the ECM then sees a possible runaway condition where the accelerator potentiometer is advancing - but no verifying off-idle trigger has occurred as expected, and also sets a code, and won't allow the engine to accelerate, and all the engine will do is start, and then idle, no matter WHAT the accelerator position.



SO, the IVS setting is important, but normally not all that difficult - and when a MANUAL IVS, such as the micro switches some of us are using is installed, it is just a matter of setting the MS to trip just slightly off the resting idle position, and then return the same way - it's a purely MECHANICAL adjustment, and absolutely no "voltage adjustment" at all!



In fact, with this potentiometer and MS setup, the actual stop screw adjustments at each end of the OEM APPS travel probably are totally unimportant, since all the ECM wants to know at setup, is the full range travel from idle to WOT, and the idle trigger setting is done by positioning the MS in relation to the belcrank.



SURE, you CAN screw up, and set the MS too TIGHT against the belcrank, and it will trigger too LATE - and the ECM won't like it - or set it too LOOSE, and it won't trigger at all - and the ECM will again not get the signal it expects for proper function - it's really not difficult, and both the pot resistance and the IVS setting don't SEEM to be terribly critical, at least not in a tight, laboratory manner.



It seems far more a common sense adjustment, where you simply set the MS to reliably trigger just SLIGHTLY off the resting idle position - voltage measurements (when using a manual MS) don't come into play at all!



NOW, that's the way *I* see it - and using those assumptions, I made, installed, and have been successfully using my own APPS for nearly 2 weeks now, without problems...

 

[KarlC]

Although it may be complex to understand, the SAE spec referenced in post 265 of this thread does show the APPS/IVS requirements. Not certain, but it would make sense if Cummins designed their ECMs to accept any APPS that meets this spec. If this is true, the allowable APPS output at idle should be 10-20% of supply voltage, and 70-85% at WOT. With a 5-volt supply this iis 0. 5-1. 0V at idle and 3. 5-4. 25V at WOT. The allowable range for the IVS switch point is above idle by 3-10% of the APPS output span (voltage range from idle to WOT). So if the APPS span is 0. 6-4. 0V, the IVS must switch between 0. 702 and 0. 940V. Clear as mud?



Here's a way to figure where the IVS switch should actuate. You need to know the idle and WOT voltages from the APPS, with a 5-volt supply attached. This can be measured with the APPS in the truck and key on. Just measure the idle and WOT voltages from the APPS. Make sure the idle voltage is near 0. 6 volts, and the WOT voltage near 3. 75 volts. Then do this computation:

1. Subtract the APPS idle voltage from the WOT voltage. This is the span.

2. Multiply the value from step 1 by 6. 5% (0. 065).

3. Add the value from step 2 to the APPS idle voltage. The result is the voltage at which the IVS should switch.



Then go back to the truck and adjust the MS to switch when the voltage from the APPS is what was computed above.



Hope this helps.



Karl

 

[mhenon]

Although it may be complex to understand, the SAE spec referenced in post 265 of this thread does show the APPS/IVS requirements. Not certain, but it would make sense if Cummins designed their ECMs to accept any APPS that meets this spec. If this is true, the allowable APPS output at idle should be 10-20% of supply voltage, and 70-85% at WOT. With a 5-volt supply this iis 0. 5-1. 0V at idle and 3. 5-4. 25V at WOT. The allowable range for the IVS switch point is above idle by 3-10% of the APPS output span (voltage range from idle to WOT). So if the APPS span is 0. 6-4. 0V, the IVS must switch between 0. 702 and 0. 940V. Clear as mud?

It's not only clear. . it's exactly what I've been reading on my voltmeter for both OEM APPS and commercial Williams APPS. Most OEM APPS have a voltage setting taped on the sensor that is around . 525v. The two OEM APPS I've checked where around 3. 70v (running on memory here but it's close) at WOT. The Williams APPS were close to the same figure . 600v and . 634v at idle and 3. 85 or so at WOT.

I had an interesting day making up my jumper cables to adapt the Williams APPS to be "plug & play" with OEM wiring. I didn't bother to install the APPS to the OEM bellcrank. I mean I just wanted to see if I wired the jumper correctly and check the voltmeter as I worked the APPS back and forth with a screwdriver. Both APPS went WAY below the usual idle voltage (like . 045v or so). I forgot to write it down. This tells me that the bellcrank takes up several degrees of play in the sensor to raise the voltage to something more suitable for the ECM. Final adjustment is made at the APPS itself. OEM APPS has oblong bolt holes for this and the Williams is adjusted with the idle stop screw. Also, on the OEM APPS if you turned the it all the way forward (WOT) with a screwdriver it would get very high and than "0"v. . like it went right off the resistance track onto the mylar. So the degrees of throw on the bellcrank keep it on the resistance tracks and somewhat in the ballpark from the ECM perspective. OK. . that was simply nice to know info. The interesting part happen the following day when I went to start the engine. Whoa. . baby. . codes all over the place and a check engine light that I had a heck of a time getting rid of. Apparently the ECM did not like these very low and very high readings. The engine ran fine but CEL stayed on for several startups until the ECM was happy again. It's not nice to mess with Mother Cummins!

The main point is Karl is right on in his last post. While there's no super critical voltage. . either idle or WOT. . there is an acceptable voltage span for idle, IVS trip points and WOT. If you're working on the edge or outside this range you will get a code. . some of them very persistent.

Mike

 

[Gary - K7GLD]

While there's no super critical voltage. . either idle or WOT. . there is an acceptable voltage span for idle, IVS trip points and WOT. If you're working on the edge or outside this range you will get a code. . some of them very persistent.

Mike

Which was why I carefully measured the operational reistances of my OEM APPS, and used those as a pattern for the one I made up to substitute... :-laf:-laf



Better to start out close, and THEN adjust, than be WAYyyyyyy out in left field from the beginning!

 

[rweis]

Today's observations:



bus APPS pot, MS IVS



This am I disconnected the batteries for 3 hours with the key on. Then I reconnected the batteries and did the key on, pedal slowly down, pedal slowly up, key off. Start and I drove about 100 miles and it functioned perfectly. No dead pedal, no codes, I thought I had an answer.



Then I drove home and had about 8 dead pedals and the 0121 code.



However when it dead pedal, I could go to idle pedal for about 2 seconds and it would pick right up again. It semed like it forgot what idle IVS was and needed retaught of idle for a second or two. I got home and checked codes, 0121 and it was clearable withthe Smarty. I bring that up because some 0121 on previous days were not clearable with the Smarty. The 0121 on the way home was.



I am going to go to the bus APPS IVS tommorrow and drive it and see if that makes any difference. NOTE: see post below in answer to KarlC. I will try to work the bus APPS into a more acceptable range and see where the MS IVS then tripps.



Bob Weis

 

[rweis]

Bob and Gary,



Obviously when set, the IVS is telling the ECM the APPS is at idle. But doesn't the ECM still start to increase engine rpm as APPS voltage is increased from the idle voltage, even though the IVS is still in the "idle on" state? Or does the ECM not respond to APPS voltage increase until the IVS is triggered? I assume it's the former.

-----------

No, the acceleration does not occur until ~. 78 volts, and the IVS is in throttle position.



I have my APPS at . 440 and it does not accelerate the engine until ~. 78 volts and the IVS is no throttle .

-----------

If that's the case, then the IVS must serve only as a verification to the ECM that the APPS voltage isn't malfunctioning and running away... right? If this is true, then maybe the ECM has a limit as to how much the APPS voltage can increase from idle before it needs to see the IVS state change to "idle on" or a DTC is set and the ECM reverts the engine to idle for safety.



Can you please clarify your understanding of all this?



BTW, today I hope to measure the voltages on my original OEM APPS while still in my truck, remove it, and then install, calibrate, and test the Williams APPS. I'll let you know how it goes.



Best regards,



John L.

Bob Weis (answer above between dashes)

 

[rweis]

KarlC -



I'll try that instead of changing to the bus IVS to see if the MS IVS will fall into the ranges discussed.



Bob Weis

 

[JLandry]

Hey everyone,



Thanks so VERY MUCH much for all the great information on the sensor voltages and IVS settings. I'd forgot about those SAE specs for the APPS. This is such a long thread... it's really a BOOK of evolving knowledge!



Unfortunately I have no progress to report yet on installing and testing a Williams APPS on my truck. I got busy with higher priorities all day yesterday... prepping our travel trailer for an upcoming trip to Death Valley in two weeks, changed all the bulbs in my truck, and cleaning off the crap (black fuzz?) which had accumulated on the front of the radiator. Today I hope to at least solder the 6 pin Deutsch connector the Williams wiring harness, and maybe if the weather holds install those taps on the truck wiring harness to take voltage measurements.



Best regards,



John L.

 

[Gary - K7GLD]

Hey everyone,



Thanks so VERY MUCH much for all the great information on the sensor voltages and IVS settings. I'd forgot about those SEA specs for the APPS. This is such a long thread... it's really a BOOK of evolving knowledge!



Best regards,



John L.

I have a much condensed version of overall APPS progress to post later today - easier reading than this LONNnnng thread, and more general in nature - maybe keep this one going for the more detailed and in-depth developments as they occur (almost HOURLY! :-laf)...

 

[rweis]

FYI:



3/24

Bus APPS, MS IVS

NO CHANGES to the idle set or the MS threshold.

APPS idle . 440 volts

Drive to work (35 min), cool temps (65*), NO changes from 100 mile drive 2 days ago when multiple 0121's but clearable: No codes, no dead pedal.



Tending to think that temp has something to do with it and that . 440 volts is on the ragged lower limit of functionality. However, I want to get it to fail like it did 2 days ago, then make adjustments to a higher idle voltage (and check against the rest of the specs) on the road and see if that makes a difference. I would like to know where the lower functional limit is so we can add that to the knowledge base.



Drive home from work 35 min, 75*, No codes, no dead pedal - go figure?



RATHER THAN ADDING POST AFTER POST DAY AFTER DAY I AM GOING TO EDIT THIS ONE POST DAY AFTER DAY UNTIL I GET THE BUS APPS AND THE MS EXACTELY THE WAY I WANT IT AT THE EXACT VOLTAGES (IDLE, IVS) I WANT TO SET.



3/25

Managed to get a 0121 this am driving in and that is good because now I have something to work with.



I made a spreadsheet last night with the 5 volt supply and then the 10% & 20% idle set points, the 70% & 85% WOT values, giving the span values and then the 3% & 10% span values giving the IVS set points. I then played "what if" with idle set points to see where that put the IVS values. I will move my idle set point from . 440 to . 510 to be just inside the 10% of supply voltage parameter. That will give me . 603 IVS set point at 3% which I will set at . 610 to be just within the IVS parameter. Which is interestingly enough is about where the dc APPS was set.



The only thing I see that might be affected is HOW the MS is mounted to interact with the bellcrank. I will have to see how the mechanical MS switch opening and closing agrees witht he . 610 IVS set point. The idle set point and the IVS set point might need to be able to be set independently and not use the frame shape of the bell crank lever for the MS switch lever to contact, something like an adjustable screw mounted ON the bell crank lever so the IVS MS can be adjusted independently. My MS mounting bracket was designed to accomodate independently adjusted MS if I needed it to, so that should not be a problem. More to come.



Drove home and got 3 0121 codes - good, finally showing the problem.



I reworked my MS this afternoon. The rework amounted to taking off about 1/16" of material on the edge of the idle set screw casting so the MS would clear the casting and moving the MS about 1/32" closer to the bell crank frame and enlarging the MS mounting hole closest to the idle set screw about 1/32" so the screw has a tiny bit of room to move for and aft so you can set the IVS voltages. The movement is really fractional. A gental tap with a 1/4" socket is pleanty. I did not have to change anything about how the MS switch was mounted except for making 1 mounting hole a tiny bit larger.



I set the idle voltage at . 580, the ECM goes into throttle at . 710. No MIL codes.



The procedure was to get the MS to be able to rotate toward the bell crank just a tiny fraction so there was some adjustability with it. Use your voltmeter on pin 23 and ground, key on.



FIRST - Screw in the idle set screw a good bit so the bell crank really does not hit the MS idle switch. You are going to set the MS IVS throttle part first. Set the MS IVS throttle to around . 7 volts or so. Work the bell crank several times to be sure it will come through the . 7 where you are setting the IVS throttle and you hear the click of the switch closing. Remember the ECM throttle up is about . 78 so don't get too close to that. TIGHTEN the MS down in its final resting place.



SECOND - start backing out the idle set screw until the bell crank can go from WOT to idle and trip the IVS idle. I found on the MS we used that the range of MS idle to MS throttle was about . 145 volts. If you set . 7 as IVS throttle trip then you should get about . 555 for the IVS idle MS trip. . 597 was about my dc APPS calibration sticker voltage was.



Third - you want to make sure the IVS idle trips so back the idle set screw out about down to . 530 or so but be able to hear the MS switch throw before the bell crank gets to idle. The MS switch will still have a good bit (1/32") before the switch bottoms out.



Don't forget to do the APPS calibration procedure.



So what we have is . 555 IVS idle, . 700 IVS throttle, ECM goes into throttle at . 710 on mine.



I guess the biggest thing I learned was you need to set the MS very close to what the dc APPS was so it meets parameter requirements and all is well.



Bob Weis

 

[rweis]

Here are the bracket adjustments to get the MS adjustability I needed:

Idle Set Screw Casting Removal

Mounting Hole Enlargement

Idle Set Screw Casting Clearance

(Notice how far in the idle set screw is turned to set the desired idle voltage?)

 

[mhenon]

Bob, have you tried running just the Williams APPS (no MS) and adjusting to get no codes. Then you could take voltage measurments from the Williams and mimic that with your micro switch.

Mike

 

[rweis]

Mike, yes see post 497. Rather than set it to what was there (which may be right or wrong), I set it to the stands that KarlC put in his post (10% 20% 70% 85% 6. 5% of SPAN etc). I wanted to see if the more universal set of standards would apply or did DC come up with something uniquely their own.



The reason I did this is someone may have a "Bad APPS", but using the set of standards they can check it against a standard to verify good or bad with nothing more than a voltmeter.



I tend to think that the DC settings follow the universal set of standards, or at least the ECM will accept the universal set of standards settings.



idle = 10% - 20% of supply voltage

WOT = 70% - 85% of supply voltage

Subtract the idle from the WOT to get the span

IVS= idle + 3% - 10% (aim for 6. 5% which is half way from 3% - 10%) of the span



Interestingly enough, my ECM voltage to be cleared to go for acceleration went from . 78 using the IVS circuitry to . 71 using the MS switch.



I did have to do the settings in a particular order: set the IVS throttle first, bolt the MS down, use the idle set screw to set the IVS idle, and found . 145 volts difference needed trip the IVS MS from idle switch to throttle switch.



The amount of movement needed to set the MS was extremely extremely small (1/32"), the difference in tightening the screw & nut tight.



Bob Weis



This morning was the first drive and it went fine. Rather than report back each drive I will only report back if something does NOT work as planned as I think the APPS standards will work fine and give us more control with everyone using the same standards.