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

[Sticks]

15w40 - Likewise, getting the assembly away from the heat and waiting for the problem is another method, albeit more expensive ($55 for plug casings and wires - OUCH).



Do you thing the dealer will buy into the replacement if the pre heating/relocating things works?



I suppose If I thought I could get away with letting the truck idle for 15 minutes while I held a heat gun/hair dryer on the APPS and see if the engine starts surging... Damage my engine that way you think? DC says not more than 5 minutes.

 

[Gary - K7GLD]

Sticks - you might consider simply ducting cooler outside air towards the APPS, using common flexible hosing from a number of sources - lots easier than relocating that whole APPS assemply. Pretty easy to modify the outer plastic APPS shield/housing to accept air from an outside source, and the housing should be pretty inexpensive to replace if it doesn't work...



I don't want to let this die - I have a couple more used APPS units, and as soon as Dave gets his schematic finished so we can get a better picture of what goes where, I want to come up with the best method to actually test one on the bench so I can verify why the ones I have here were replaced, and if it seems it was because of the same erratic operation being discussed here, want to do the drill/inject cleaner bit to verify its effect - then offer them to guys with APPS problems willing to install and try them...

 

[15w40]

Sorry for the delay in posting info on the APPS. I hope to have the schematic posted next week. I just failed a safety inspection for ball joints and I will be replacing those early next week. That takes priority over the APPS.



I began a more complete dissection of the APPS after finding that pin 1 was not making a good connection to the circuit inside. A measurement showed that the resistance would change as I applied pressure the pin. What I found was a problem right at the connection point to the brass pin. The photo below shows the flex circuit pulled back from the “Zebra strip“-contacting pin 1. For those wondering what a zebra strip is, it is alternating layers of white insulating rubber and black conductive rubber. Compressing the zebra strip between the two metals makes contact in only one direction. It appears that the contact in the area of pin 1 was not reliable although measuring only the zebra strip shows less than 1 ohm in that area. This may have been the reason this APPS was replaced. The good news is I will be able to test a functioning APPS if this is the case.



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[Gary - K7GLD]

Dave when you get time for a reply, exactly how does the strip physically connect to the pins, crimp, solder, or some other method?

 

[15w40]

Gary, there is no crimp or solder connecting the flex circuit to the zebra strip. The flex circuit folds up from the plane of the potentiometer and circuit by 90* and enters a slot. This slot is backed by plastic section. My guess is the platform holding the circuit also has the 90* section attached. This section applies pressure to the back of the flex circuit as the 6 brass connector pins are pushed against the zebra strip. I am also guessing that the pins are held in a jig as the black plastic is injection molded into the APPS mold cavity. This will insure that the pins and circuit will ALMOST always make a good contact to the zebra strip.

 

[Gary - K7GLD]

AHHhhh - the old push-in type connector where the edge of the film is exposed, and you HOPE a good solid connection is made when you push it into the female part - talk about a POOR choice for reliability... Another bad mark for DC/Cummins...

 

[Sticks]

No, please don't let this die. I started it and I want to see the solution found. I have just hit the wall as far as my capabilities go for testing them.



Gary - I was also thinking of a small 12v fan mounted close to it as well. I still want to try to remove it from the radiating heat though. I have the parts for an extension so it's not like making a bracket will kill me effort wise.

 

[Gary - K7GLD]

A cooling fan will merely circulate the underhood heated air over the APPS - using hosing to bring in outside air will provide cooling. Real easy to rig up a temporary setup to see if it helps, then a permanent one if it does...

 

[Scheibins]

Originally posted by sticks

Guys, I think we need to seriously need to take heat into consideration here.

Mine has been surging for about 4-6 months now. If has dropped to idle, thrown a code and the CEL, THREE times in this time period. Sometimes at idle it jump 50 to 100 rpm and I notice it at light throttle as well. You know, all the normal stuff .



Anyway, I've being watching the tread for a while and appreciate all the good info guys. Sticks you may be on to something with your truck, but I'll tell ya I've noticed surging before I even get out of the neighborhood. ~~60 seconds after start, about an 1/8 mile.



Thought I'd throw in a little for this thread.

 

[Sticks]

I have 10 scans just like this from different runs. Info was collected with my Alex Pepper OBD-2 software. Free download to read files. PM me if you want to see the scans in action and I will e-mail you the data files from my runs.



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[Gary - K7GLD]

STICKS, now I *am* confused!



Your first PC scan shows erratic operation while under cruise control operation - and I thought we had pretty well established that the APPS was out of the comtrol loop when CC was engaged...



Sigh, back to the drawing board I guess! Or else you have some other problem than APPS!



PLUS, the info from Dave about the connection, or lack of it, at the pin connector, is discouraging as well. The ability to drill and spray cleaner at the contact fingers had definite possibilities - but doing anything to affect the contact at the plug is considerably more difficult, other than flooding the insides of the APPS with contact cleaner and hoping some works down into the plug attachment area and improves contact...

 

[Gary - K7GLD]

OK, after some thought, a question/theory...



Sticks, exactly WHAT/where are you sampling for the graphs you posted above? One seems to be labeled operating with the cruise control engaged, the other is labeled "idle"



I can sorta understand why the line display would be jagged in CC, since the ECM would be constantly making minor running adjustments to engine fueling/RPM to maintain a steady speed - not a "flat line" as with an old-fashioned throttle cable that merely holds the throttle to a single selected position, regardless of engine RPM...



So, what exactly WAS that graph monitoring?

 

[pharlacher]

Injection Pump

Truck won't start. Getting Error codes 1688, 1689 and 237 water in fuel light is on and I have a FASS and not using the stock filter. . Have been getting error code P0236 for a couple of weeks Figured I was going to need a new injection pump and ordered one from Piers today. Truck was running great so I told him I could wait a couple of weeks. Piers if you read these I need a pump as soon as you can get one to me. Anyway I am sitting here waiting for the tow truck to come and drag my truck home. Can anyone help me and confirm that this is an injection pump problem? I have never seen the po237 before and I think it has to do with the turbocharger. Also, I never got a warning, truck was running great just kept getting the p0236 code. Is there anything else I should be looking at? Truck has 93,000 miles. 2500 4X4. TST level 1, B&d torque converter and valve body, RV injectors, 4 inch exhaust, AFE intake filter. I hope it is only the injection pump, I ordered a high output form Piers. I figured if I had to change it why not add a little more ump. What makes the damn thing just die? No black smoke, no stumble, nothing..... figured I had some time. stupid me. .

Thanks in advance Help. .

Paul. . walking in Simi Valley already having withdrawl pains... I hope I am doing this right

 

[pharlacher]

Gary, sorry about the last post. New at doing this. Please ignore it. Paul

 

[Sticks]

Originally posted by Gary - KJ6Q

OK, after some thought, a question/theory...



Sticks, exactly WHAT/where are you sampling for the graphs you posted above? One seems to be labeled operating with the cruise control engaged, the other is labeled "idle"



I can sorta understand why the line display would be jagged in CC, since the ECM would be constantly making minor running adjustments to engine fueling/RPM to maintain a steady speed - not a "flat line" as with an old-fashioned throttle cable that merely holds the throttle to a single selected position, regardless of engine RPM...



So, what exactly WAS that graph monitoring?

The graph is monitoring the APPS sensor output not what the ECM/PCM decides the engine is running at. The OBDII software samples the sensor about 3 times per second. If I add another sensor (RPM, Speedo, IAT, MAP... ) then it samples each one about once per second, and it gets slower for each additional one I add. That is why I have only been monitoring the TP% because the spikes rarely last for more than one second.



My cruise control is all electric. So the APPS sensor has no effect on the engine operation until it is depressed past the point that the ECM/PCM (whoever is controlling the engine speed with the cruise engaged) is operating, and the cruise control has no effect on the APPS readings. I apologize, when I refer to "Idle" I mean foot is off the throttle, and the APPS assembly has returned to zero. So in the above scans, the cruise control is engaged on the highway at 75mph, my foot is off the throttle, and the APPS output is jumping all over the place in the top one, and the bottom one, I am still running down the highway at 75 with the cruise, and the APPS output returns to normal.



I have scans with the truck sitting still, and FOT (foot off throttle) at idle, and the scans look the same (and the percentage numbers are the same), only the RPM's are jumping from 800 to 1200 and anywhere in between. Sometimes it will hold the higher revs for a few seconds then drop off, others it just jumps up and down like I am goosing the throttle.



Variations of . 4% does not make a noticeable difference - running normal and the TP% in the scan shows 9. 0 - 9. 4 and looks like an EKG. Variations of 4% (9. 0 - 13. 0) makes for an irritating drive, annoying at stoplights, and a bit harrowing in stop and go traffic.

 

[Blackbird]

Hi gang -

What became of this thread? I now find myself in this position.



Jay

 

[Sticks]

Since I am walking the tightrope of being able to keep the truck/having to sell, I have stopped all work on it.



Gary has several that are available as guinea pigs, and I am staring at the parts to do a APPS relocation to get it away from the heat, and mount it so any dust that it scrapes up will fall away from the sensor and fingers (turning it 90*).



I still have the same problem and it goes away after getting heat soaked - Drive until the engine is up to temperature, park for 1/2 an hour or driving for 1 hour. Stays gone until the engine cools down.



There was another thread by mgonclaves that showed a 216 code that turns out to be the APPS, and another that had the same symptoms as us, but was the wire harness to the VP44 (got chaffed/crimped)... which could be my problem since this all started for me after my vp44 replacement.

 

[Gary - K7GLD]

We're leaving early tomorrow morning for the Oregon coast, will be gone for over a week - just in case anyone tries to contact me for the APPS or anything else - still have 2 up for grabs for those willing to try them and either exchange their old one or return what I send out if it doesn't help...

 

[15w40]

I have dropped the ball on the APPS schematic. Things have been hectic and I just have not had the time to do a good job in analyzing the circuit. It has been a while since logging on to the TDR forums and I just received an email from this thread.



If anyone is waiting for me, give me a couple more weeks to finish and post how the APPS works along with a schematic. One problem in reverse engineering a circuit is that often the components are not marked in any way. These components are bought in bulk by the circuit maker and are cheaper if the cost of marking the component is eliminated.



Here is a list of things left to do:

1. Remove several components that are mounted upside down or not marked to determine values.

2. Remove capacitors to measure values independent of circuit parasitics.

3. Remove some unmarked components that appear to be ESD devices and test them using a curve tracer.

An ESD device (Electro-Static Device) is used to soak up damaging electrical spikes before they can damage transistors and other components.

4. Reassemble the APPS and power it up to document its operation.

5. And finally, see if there is any way to fix or repair the APPS.



With the schematic and knowledge of how it works, it may be possible to adapt the much cheaper APPS from an earlier ISB. These can be purchased from Cummins for about $40. I am not holding my breath on this one. The newer ECM may require more than just a potentiometer and an idle validation switch. At least it should be possible to work out a strategy of testing a questionable APPS before just swapping it out and hoping for the best.



The APPS that Gary has sent to me has a label on the cover that shows “0. 564 Volts” I believe this is the APPS output with the throttle not pressed and tells the ECM to go to an idle. One common problem with Op-amp circuits that are exposed to periodic heat and cold is a shift in offset voltage. To put this in other words, the change in voltage from 0. 564 to a new and incorrect voltage may confuse the ECM and create a problem. I hope to measure the reassembled APPS to see if this could be the problem.

 

[Blackbird]

Originally posted by 15w40

With the schematic and knowledge of how it works, it may be possible to adapt the much cheaper APPS from an earlier ISB. These can be purchased from Cummins for about $40. I am not holding my breath on this one. The newer ECM may require more than just a potentiometer and an idle validation switch. At least it should be possible to work out a strategy of testing a questionable APPS before just swapping it out and hoping for the best.



The APPS that Gary has sent to me has a label on the cover that shows “0. 564 Volts” I believe this is the APPS output with the throttle not pressed and tells the ECM to go to an idle. One common problem with Op-amp circuits that are exposed to periodic heat and cold is a shift in offset voltage. To put this in other words, the change in voltage from 0. 564 to a new and incorrect voltage may confuse the ECM and create a problem. I hope to measure the reassembled APPS to see if this could be the problem.

Dave -



I just had to install a new APPS. Would any readings off a new one help. Let me know if I can help.



Jay