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

[Sticks]

Well I just got finished cutting open a late model APPS sensor. These things are definitely well built, and absolutely are not serviceable. I was hoping to maybe split the seam, or cut a hole to gain access, but no dice.



I took some pictures, and I need to retake a few for better focus. I will post those tomorrow.



My conclusion is that there is a design flaw in the brushes, or they are meant to fail. The brush portion of the unit (4 separate brushes, with 3-4 fingers each) have what could best described as hooks on the ends. Instead of bending away from the contact surface (like skis), they bend toward the surface, thus scratching/scoring a grove in their travel path. All of the little fingers had a significant amount of buildup in the hooked end, and the contact surface had groves cut in it. This supports my theory that the brushes are losing contact with the surface, or bridging and giving us the RPM jumps.



I am going to take the remains to Cummins next week and see if the sensor part can be purchased separate from the entire assembly (throttle cable bracket).



TO BE CONTINUED!

 

[#2DSL]

Yea find out why they cost so much too.

 

[jrobinson2]

Are you sure the pad is not worn completely away leaving only the hook, I have seen several fuel senders like this.

Jared

 

[zstroken]

is it a copper plate that they run on? The scrapers could be used to keep the oxidation off of the coppper

 

[Sticks]

jrobinson2

Are you sure the pad is not worn completely away leaving only the hook, I have seen several fuel senders like this.

Jared

Having never opened up a new one, or know how they're were built, I don't know. The ends of the fingers (copper) look like they were treated (anodized), or plated.

zstroken

is it a copper plate that they run on? The scrapers could be used to keep the oxidation off of the coppper

No, the plate is not copper. It is a black substance adhered to the type of material that they make the flexible connections out of. Like a ribbon. In fact the entire circuitry is made of microcircuits and the ribbon as opposed to a hard circuit board. I did notice on one end of the contact side, that it was not attached to the APPS housing. It had a swell in it.



I will try to get some close up pictures of it today. My camera does not like to take pictures at point blank range.

 

[Sticks]

As promised here are the pictures.



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This is the complete unit from DC. The sensor screwed to the back is the actual sensor, but whe have to buy the whole damn thing.



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There is a lot of adjustments that can be made when mounting to the housing. Horizontal, Vertical, and clocking. I would imagine it would be a PTIA to do.



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Inside is the sealed bearing and the shaft that connects to the throttle body.



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This is the bak of the sensor after Imade a cut along the seam that was evident along the edges. They used a very stong glue that did a wonderful job of holding it in place. Ihad to make a second cut with a different bit to cut through the entire seam.



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This is the cover removed from the back of the sensor. Nothing to do in here. The circuit board is the super thin "ribbon" material.

 

[Sticks]

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This is the side that goes to the shaft on the APPS housing. I did not get a good picture of it before it got cut. The peice laying on top is the outer spindle housing with the return spring. There was no seam, or snaps that I could grind or undo.



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I had to remove a second plate under the first one to remove the brush assembly. This exposed the contact plate. The brush has 4 arms with 4 fingers each.



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From Left to Right. Outer cover with the return spring, inner cover, brush spindle, sensor.



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Sorry for the poor quality,. I can not take closeups. This is the side of the spindle that has the brushes. You can almost make out the different fingers on the left arm.

 

[Sticks]

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The four dark arc's are the surface that the brushes ride on. The brushes fingers are bent towaards the surface instead of away (like skis) All of the fingers had a large amount of buildup on the inside of the bend, and the contact surface has visable grooves/scoring from the fingers. You can see the travel path that the brushes moved most.

 

[Gary - K7GLD]

It all make sense except for the part about the fingers contacting the carbon tracks - this is nothing more than a large dual element potentiometer - similar in construction to the volume control in a radio - this type seems to use an inner and outer track, apparently 2 independent controls that track each other as they are rotated. The usual physical contact SHOULD be a smooth non-invasive motion/contact that permits good contact with minimal damage to the carbon resistance material the fingers ride upon - can't understand why the one you took apart is the way it is, unless it was defective from the beginning...

 

[d.miner]

Sticks,



How many miles on your unit when this was taken out?



I've steamed my engine compartment before and have been concerned that I may get moisture in this unit, did you see any signs of moisture? (assuming it's in the engine compartment)



Please let us know what you find out from Cummins... I'm always looking for a more cost effective solution.



Thanks, Dan

 

[Weidner]

I still need my TPS replaced

I had my tps or "apps" act up one night a few months ago. Lost all throttle response, re started the truck and it was all good. Every once in a while in hard acceleration, I will get a stumble in throttle response. I will be getting one sometime soon. I have a friend at a chrysler dealer that is helping me get a deal, employee price is $291. Still more than I want to spend!!

 

[Gary - K7GLD]

These trucks should NOT be having these problems so early in their lifespans!

 

[Sticks]

Originally posted by Gary - KJ6Q

It all make sense except for the part about the fingers contacting the carbon tracks - this is nothing more than a large dual element potentiometer - similar in construction to the volume control in a radio - this type seems to use an inner and outer track, apparently 2 independent controls that track each other as they are rotated. The usual physical contact SHOULD be a smooth non-invasive motion/contact that permits good contact with minimal damage to the carbon resistance material the fingers ride upon - can't understand why the one you took apart is the way it is, unless it was defective from the beginning...

Or as I like to call it, an over grown rheostat.



I am annoyed that the fingers hook down and drag/scrape, instead of riding on the tracks.



Designed to fail, or someone in quality control fell asleep at the wheel and they are being manufactured WRONG!



I received it from another TDR member who replaced his. No way was I going to dissect a functioning $400 unit for the entertainment.



Cummins no-longer even carries this sensor assembly. Dealer only! I am going to do some research on this sensor. This can not be a Dodge CTD item only, this has to be a common sensor, we just need to find out what other vehicles it is used on.

 

[Sticks]

Originally posted by d. miner

Sticks,



How many miles on your unit when this was taken out?



I've steamed my engine compartment before and have been concerned that I may get moisture in this unit, did you see any signs of moisture? (assuming it's in the engine compartment)



Please let us know what you find out from Cummins... I'm always looking for a more cost effective solution.



Thanks, Dan

As I said above, this was a donor from another TDR member. The way it is assembled on the truck, you would be very hard put to get any moisture inside. It is way too sheltered. Having said this, when I did take the sensor off the housing, there was a little moisture on the outside of the spindle where it attaches to the shaft. There is also no way to spray some contact cleaner inside to clean the tracks. You would have to drill 1 or 2 holes in it to spray and drain. If anyone wants to try that on theirs, let me know and I will take some measurements to see where the safe points are to drill for spraying and draining, then you will have to figure out something to plug the holes.

 

[Sticks]

As soon as I find another source or part number for just the sensor, I will post it. If anyone else has friends at a dealer, or a NAPA or other auto parts store that will LOOK in a book, not the computer (clerk at cummins said that some catalogs will have a cross reference in the books for TPS sensors) and can get them to do some legwork that would be a big help for all of us.



DC has us by the proverbial balls (sorry ladies) on this one. At this point there is just no way around it. Might explain the huge price tag on it.

 

[Gary - K7GLD]

DONCHA just LOVE these expensive, sealed components that are not serviceable! The ECM is another great example of a high-dollar assembly of 10 cent parts that MUST be replaced as a unit at great cost, rather than simply working on/replacing the lone individual component that is really causing problems...



One of the by-products of a throw-away society...

 

[WestTN]

sensor construction

I would like to have had better pictures of those fingers. I can't make them out from the pictures, but the description makes it sound like they were installed incorrectly. The graphite-bearing resistance media would never stand up to a feeler that contacted it in a scraper fashion. It that is indeed the condition which existed then the sensor was most likely a misassembled factory defect. That would explain early failure.

 

[Sticks]

Re: sensor construction

Originally posted by WestTN

I would like to have had better pictures of those fingers. I can't make them out from the pictures, but the description makes it sound like they were installed incorrectly. The graphite-bearing resistance media would never stand up to a feeler that contacted it in a scraper fashion. It that is indeed the condition which existed then the sensor was most likely a misassembled factory defect. That would explain early failure.

It just scares me to no end that it is either a boo boo at the manufacturer from the initial setup of the assembly that never got caught - so all of the sensors are made this way...



-OR-



DC engineers made it this way, or they are aware of the way that it is made, and know that it will fail after "X" number of passes.



I will try to get a better picture of the brushes. For now, here is a simple drawing.



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[Gary - K7GLD]

It's easy to see what you are describing - what's HARD to understand, is WHY they would be installed that way! I've seen a number of potentiometers using similar "fingers" for contact, but always using a slight bend on the end that allows smooth contact and long wear. Does it appear as though those contacts are capable of being installed into the rotating assembly in the reverse position, as though it was an assembly defect - or is that the ONLY way they can be assembled?

 

[Sticks]

It is a very tight unit. The arms almost look like they are part of the mold (READ - inserted in the mold) when the plastic spindle is made/poured.



I may take the cut off wheel and do a cross cut on the spindle to see how the arms are set in the plastic.



Man I wish I had a $1000 digital camera that I could take some quality closeups.