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

[rweis]

So the physical attaching the "board" to the APPS body is not REALLY well done? A warped board would probably hasten the failure as the contact finger is no longer running smoothly. Interesting.



You gotta love it!



I wonder if the "other electronics" on the ABC-Bus TPS are the same? since supposedly "compatable" with ISB. Might be one piece of the puzzle to get the other electronics out of the heat.



Flood the APPS with OAT? after shutdown? (sounds like something we have already done to the VP44, part #2)



Bob Weis

 

[Gary - K7GLD]

Flood the APPS with OAT? after shutdown? (sounds like something we have already done to the VP44, part #2)

YUP - like this in my case:



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And here's what the APPS/bracket looks like from the front side:



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Obviously, the actual APPS module is not visible, it's mounted on the rear side of the above bracket, between that bracket and the engine:



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UNFORTUNATELY, the APPS module, as installed on the Cummins, is rather enclosed and confined in the cavity formed by the fixture the APPS bracket attaches to:



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SO, the major cool airflow is pretty much limited to the front side of the mounting fixture - but since the APPS is rather tightly held to that fixture on the back side, we can only hope that there's enough conduction of cooling applied to the front side being subsequently also applied to the APPS itself.

 

[JAG1]

I'm a real greenie about electronics... . do you tink Dodge engineers designed this APPS kinda this way to help support the dealers? Either by service/ parts or causing some to just trade in thier trucks? I had a dealer owner son inlaw tell me how they deliberatly don't correctly repair some vehicles (the more sought after ones) so you'll be inclined to trade it in.



Seems like the cost of this part, being made such as it is, is very excessive and unfair.



Between this APPS (planned obsolescence) and the VP, seems like there should be a class action suit

 

[mhenon]

The tag on my TPS called for . 524v at idle which I adjusted roughly by rotating the TPS and locking it in place. I made the final adjustment by tweaking the idle set screw on the bellcrank arm. It was surprising how small movements of the set screw caused huge changes in output voltage.

If I had to guess at how this idle validation thing works it would go something like this. The TPS are probably checked during manufacturing to see at what voltage the IVS (idle validation signal) signal will trip to idle. There's only two states in IVS system... idle on & idle off (idle off meaning it's now OK to accelerate). Once that idle voltage is obtained a tag is printed up with an adjustment setting that is X% lower than the actual voltage required to hit idle. This assures that when you let off the pedal and the bellcrank hits the idle stop all fueling stops until idle RPM is reached.

So lets take my APPS as an example. When tested at the factory the IVS went to idle at say . 655 volts. If a 20% lower figure is used, to assure we're really at idle, the tag on the TPS would show an idle adjustment setting of . 655 -20% = . 524v. This would explain why those folks who couldn't adjust to the exact figure on the APPS tag still had a functioning idle. Without knowing it they were still under that trip figure yet not too low to throw a code.

This is all speculation of course but seems to make sense to me.

Mike

 

[rweis]

I do not know about the %'s, but that is how I understand the voltage adjustment as well.



Over on the PCM I soldered a pigtail wire to the wire you are suppose to check to adjust the APPS rotation against. I did this so I can just clip an ohm meter to the pigtail and do the rotation adjustment. Takes about 20 minutes.



I am going to ABC bus tommorrow. I need a little guidance of exactely what I need to look for. I printed off the link. And was going to approach them trying toget an idea of what they might have that would interface with the ISB. Then we (TDR) would see how to mechanically install it, or.



With this thread and the comments about heat on the APPS, and that I already have a blower on the VP44, I think I am going to cut some fairly large holes (1") in the APPS mounting frame to get more air over to the APPS sensor for cooling.



Bob Weis

 

[mhenon]

I'll PM you Bob.

 

[KarlC]

Does anyone know what the internal op-amp circuitry is for? Is it only for the IVS output or is it involved with the throttle position signal as well?



It might use one of the op-amps (there are four in the IC) to "buffer" the signal from the potentiometer, to give the ECM a cleaner signal to work with. If this is the case, measuring the resistance at the terminals probably isn't going to give meaningful information.



If this is the case, to properly test it one would have to provide power to the assembly and measure the voltage output as the potentiometer is rotated.

 

[Gary - K7GLD]

Does anyone know what the internal op-amp circuitry is for? Is it only for the IVS output or is it involved with the throttle position signal as well?



It might use one of the op-amps (there are four in the IC) to "buffer" the signal from the potentiometer, to give the ECM a cleaner signal to work with. If this is the case, measuring the resistance at the terminals probably isn't going to give meaningful information.



If this is the case, to properly test it one would have to provide power to the assembly and measure the voltage output as the potentiometer is rotated.

That's what I suspect as well - especially since ALL of the several supposedly "bad" APPS modules I have each display what appears to be a smooth resistance change as the potentiometer is rotated.



By the way, anyone wanting the actual physical rotating degrees as normally applied to the APPS module (I estimate about 90 degrees), can look at the photo at the beginning of this thread to see the resistance tracks on the circuit "board" - I don't have any easy way to accurately measure degrees of arc...

 

[mhenon]

Karl, i just built a little 5V power supply to do just that. I'm trying to locate a connector with pigtails now to supply the power and have access to the pins for testing.

I really want to know where the idle validation trip figure sits for any given TPS. If this changes over time (heat cycles, drift, whatever. . ) than the adjustment voltage on the TPS tag might become meaningless after long term use. By resetting the voltage to say a lower figure than is on the TPS the whole thing may come to life again.

Of course once the potentiometer wears out the games over. Then we just need to figure a way to get an aftermarket potentiometer to control a remote TPS. Easy!

Mike

Mike

 

[KarlC]

Gary,



If you measured smooth resistance change at the connector terminals without power to the unit, then the potentiometer is probably connected directly to the output, just as the scematic link above shows. No hidden circuitry there.



If you've got one to play with, you might try the following. Connect a wire between the power terminal and the ground terminal, and connect an ohmmeter between the potentiometer output terminal and the ground terminal. Then rotate the shaft until the ohmmeter reads the highest resistance, which should occur near the center of the potentiometer's range. If there's no other circuitry in the act and the potentiometer resistance is linear with rotation, this resistance should be 1/4 the end-to-end resistance of the potentiometer.

 

[Gary - K7GLD]

Karl, i just built a little 5V power supply to do just that. I'm trying to locate a connector with pigtails now to supply the power and have access to the pins for testing.

I really want to know where the idle validation trip figure sits for any given TPS. If this changes over time (heat cycles, drift, whatever. . ) than the adjustment voltage on the TPS tag might become meaningless after long term use. By resetting the voltage to say a lower figure than is on the TPS the whole thing may come to life again.

Of course once the potentiometer wears out the games over. Then we just need to figure a way to get an aftermarket potentiometer to control a remote TPS. Easy!

Mike

Mike

Mike, I'd sure like to see your results if that works out - I have several used APPS modules, and I'd sure like to check them out.



I sorta suspect these APPS modules just MIGHT not really be bad, but victims of a DC service department simply substituting less expensive parts before swapping out a bad VP-44... :-laf

 

[mhenon]

... . I sorta suspect these APPS modules just MIGHT not really be bad, but victims of a DC service department simply substituting less expensive parts before swapping out a bad VP-44... :-laf

That's what I'm thinking. When I posted last week with APPS problems (dead pedal) it was suggested to first check adjustment as per the tag voltage. I went right ahead and ordered an new APPS first. Smart huh!

Anyway, when I did re-adjust the base setting i noticed how easy it was to get the voltage way over or under. If the base voltage has drifted or moved close to IVS voltage you could trip it to idle while still accelerating or trip to accelerate while at idle. Either way it works the ECM would see the discrepancy, throw a code and default to idle. Take that to the dealer and "you have a bad APPS. . that'll be $400. 00 plus labor thankyou and no sir, there really is no way to adjust that part. . it's replace only". Sad thing is they're not even lying. The sticker right on the APPS says to make "No" adjustments.

Boy... I didn't know owning a million mile engine would be this much fun!!!! Actually I enjoy the challenge.

Mike

 

[rweis]

While ya'll work the electronic end of this thing, I am going to work the environmental temperature of the TPS end.



I already have a blower to the VP44 and can actually use the VP44 to COOL fuel if traveling over 40 mph (ram air volume becomes more air volume than blower driven air volume).



I will take my TPS bracket off and drill 1" air passage holes in it. I wrapped the entire VP44 with a industrial thermal blanket and can effectively keep the engine heat off the VP44. In addition I flood the VP44 inside the blanket cacoon with OAT. I will take the TPS off and put the entire VP44 and TPS in the thermal blanket and flood them both with OAT to see if it will help stabilize the TPS.



I will first reset the TPS rotational angle to match the voltage sticker to use as a reference point. I can very easily check the reference voltage with my pigtail to see if the TPS drifts. I will also hook up the ohm / voltage meter full time to see how the TPS resistance / voltage changes as you drive / engine heats and cools. Might give some real time ideas?



I'll try to package the thermal approach so it can be used as a "kit" for others if they want to take that approach.



"Boy... I didn't know owning a million mile engine would be this much fun!!!! Actually I enjoy the challenge. "



Me too,



Bob Weis



Does anyone remember if there seem to be more APPS failures in the summer time like it is for the VP44? or is it generally pretty evenly spread across the temperature year?

 

[Gary - K7GLD]

Bob, The BEST venting effort would probably be that engine-mounted piece the APPS bracket attaches to - drill THAT thing with appropriate holes, and then it would be pretty easy to flood the actual APPS module with cooling airflow...



I'll be on the lookout for a spare APPS engine bracket, in case fooling with the APPS bracket itself proves to be a mistake... :-laf:-laf

 

[rweis]

Like horizontal drilled holes?



I'm getting the thermal blanket ordered today and think I am going to go down fender side of VP44, around under the VP44, up between the VP44 and engine, put blanket between APPS bracket and engine mounting holes, come over APPS, connect with tail of the blanket.



I then put a thermal cover over the incomming air from the front to keep that heat out.



Then I am going to build a hose bracket this time. Last time I used A/C duct tape, but that has to be renewed every year because the glue starts to fail.



So the OAT flood then exits the firewall end (only place it CAN go) away from the heat.



I can keep the heat soak off the VP44 really well, and the circuit board in the APPS might need the same protection. Might not be the wipers at all? Who knows?



Bob Weis



Let me get this setup. Then I would be interested in trying one of the "failed" APPS to see if it is a heat problem. Oh, Gary, yes if you could save me a APPS mount I would appreciate it. I generally don't get the first try well designed and take two iterations to get it right. Maybe 2 brackets?

 

[mhenon]

Anyone know where I can order that OEM electrical connector that goes to the APPS? Actually I could use both male and female ends if I decide to relocate the APPS.

Checked with NAPA but all he wanted to do was call the dealer. Is there an online supply house that stocks oddball connectors like that. I don't even know what it's called.

Mike

 

[Gary - K7GLD]

Like horizontal drilled holes?

Actually. I was thinking a row along the top of that mount/bulkhead - I *think* it is only closed on the sides and top, with the bottom open. And since in my case, I'm already blowing a good flow of outside air up towards the bottom of the APPS, just drilling vent holes in the top of that bulkhead should greatly enhance airflow back in the cavity where the APPS module lives...



As to locating and buying spare APPS engine mounts, not sure of availability - guess we need help from the 24 valve guys who have converted to P7100 pumps... :-laf:-laf

 

[Gary - K7GLD]

Anyone know where I can order that OEM electrical connector that goes to the APPS?

I've had good results in the past using a Google search on "Automotive connectors"...

 

[rweis]

Well, went to ABC Bus and got the TPS. The TPS was $100. 96 + tax. The part # 10693907 was a good number. The accelerator pedal complete was $623. 15 (I did not get that). The accelerator pedal part # changed from 10588255 to 10970306.



The TPS is from Williams Controls WM526 Electronic Foot Pedal Assembly.



I think it will hook right up to the ECM harness (have to change the end connector on the ECM harness).



While I was there another customer came in and I asked him about TPS's. He ran a bus company and said in his opinion the Williams is the ONLY one to go with. In his busses the others last weeks to a few months. The Williams last him about 2 years. He runs his busses 20 hours a day / 350 days a year.



He was well aware of the DC TPS and did not have a very high opinion of them (the TPS's).



Now I have to figuer out exactely which Williams connection go to which ECM connection.



I am also going to wrap the entire VP44 and TPS in thermal shield blanket to keep the engine heat off them, and of course run the bilge blower into the thermal shield blanket to flood it all with OAT and stop the after shutdown heat soak.



Looks we might have a pretty good handle on this TPS thing. A little circuit alignment and we are DONE.



Bob Weis

 

[rweis]

Found the accelerator complete for A LOT LESS, like $264.



Where we go from here:



I am going to test mounting the new APPS on existing APPS bracket for the auto transmission guys because we need the TV cable linkage.



Mike is going to order the complete accelerator (pedal &APPS) and mount it in the cab and dispense with the DC throttle pedal and APPS totally for the stick shift guys.



We have to order the connectors to get the wiring into the DC harness.



Then we have to test the two parts of the project.



The wiring diagrams are compatiable, we have to measure some voltages to be sure they match, but way closer.



Bob Weis