I took my APPS off with the intention of resetting it to the proper voltage as tagged on the side. I also wanted to setup a "high idle" switch to idle the truck up to about 1200 RPM with the flick of a switch. I reset it the APPS no problem (it was reading like .3 V and supposed to be at .519V).

I got the high idle by hooking up a ~130 ohm resistor to the APPS sensor ground (wire #4 - http://xj.cdevco.net/apps/apps.gif) and that seemed to work by effectively raising the output voltage to about .70-.75 V vs. the idle of 0.5V. I tested it in the engine bay and it worked; when I put everything back together with the wires going into the cab and the resistor on a switch , hooked up the APPS and turned on the ignition, I got a reading on the #4 sensor ground wire of 4V. The truck actually won't let me start (not that I have tried but the wait to start light flashes, and the fuel pump does not prime it self for 1-2 seconds like it normally does). So I took my wiring off, and now I am back to "stock" with the same results. Tried disconnecting the battery for 2 days and still nothing. If I actually disconnect the APPS completely, it'll let me start. It's when I hook it back up that it doesn't let me.

I took the APPS off and did some readings:
#3 - APPS Signal to #4 - APPS ground - IDLE: 360 ohms
WOT: 2.1K ohms

#4 - APPS sensor ground to #5 - APPS sensor supply: 2.62K ohm

#3 APPS signal to #5 sensor supply - 2.5k ohms IDLE, 700 ohms WOT

These readings seem to be correct (?) as far as I can tell. Any suggestions?

At this point I cannot drive my truck. Not ready to drop $350 on an APPS that seems like it works according to ohmeter readings.

 

Well here's the update

The APPS SENSOR GROUND when hooked up to the truck/ignition on, was reading 4V instead of being a ground.

This is a ground supplied from the ECM. Coincidently, the idle validation switch ground is also dead now. Since both of them "broke" at the same time, it suggests that its a problem with the ECM since these both get their grounds from the ECM. Or, wherever the ECM gets its grounds for these 2 sensors. I checked continuity between other sensor grounds on the ECM and these 2, and I think that only these 2 had continuity. I then tried hooking these both up to a regular battery ground, and everything "works fine." As in, the idle voltage went back down to 0.5 V, the check engine light went away (no codes). I don't think that is the "proper" fix to my problem though.

Does anyone know where the ECM gets its ground for these? I would like to check upstream of the ECM but have a feeling it is within the ECM and that I fried it (?). The wires are #11 and #32 on the ECM.

Anyone know what my replacement options are? I beleive I will have to get a new ECM.

 

The ECM in every vehicle supplys the grounds to sensors, etc., they complete the circuit, I think you fried it.

 

For the price of a new ECM, you might as well get a MAD ECM.


phox

 

I think I fried the ECM too. I'd like to verify this by finding out which PIN is the ground to the chassis ground that the ECM it gets its ground from that provides the APPS sensor ground (32) and idle validation switch ground (11) with. If that ground is a good ground where-as the others are 4V, it's got to be the ECM. Does anyone know which pin it is?

Looks like the price of the stock ECM is about $400. Maybe I could go with a Cummins ECM (?).

I will have to check on the prices of a mad ECM with no core. I might get a MAD Ecm and sell my Edge if I can do that for significantly less than $400.

Then there is always a junkyard ECM...

 

I doubt you fried the ECM. I suspect you fried the throttle position sensor.

I hooked my APPS up wrong on my truck when I first did it. No problems because of it. The ECMs are pretty tough.

 

I am still not positive here but pretty sure it's the ECM. No clue what on earth I did.

The APPS seems to be fine based on a number of tests.

The ECM is giving me +4-4.8V on my #11 "sensor ground" pin and #32 pin "APPS sensor ground" grounds now. I'm pretty darn sure these should be true battery grounds (provided through the ECM but ultimately go to the chassis or - on the battery). Worse yet, the MAP sensor and other sensors share the #11 ground with the APPS idle validation switches, so they are also getting +4.x Volts where they should have a ground.

Anyone want to stick a voltmeter on the APPS or MAP sensor ground for me and confirm that it is 0 V when the ignition is switched on.

 

"The ECM is giving me +4-4.8V on my #11 "sensor ground" pin and #32 pin "APPS sensor ground" grounds now."

Don't worry about what the voltage is from the "sensor gnd" is to vehicle GND. Measure the voltage from the sensor ground to the sensor supply on both channels and see what you get. It should be 5V if I remember correctly.

You can't measure the resistance of the throttle sensor because it is an active component, ie there is a circuit in there that supplies voltage to the ECM. I suspect you burnt out the op amps in the TPS.

The "sensor grounds" aren't necessarily at 0Volts with respect to vehicle ground because it is isolated and has protection circuitry.

 

Thanks for the reply.

I think my ECM is screwed up regardless. i asked for a electrical engineer friend's help and he ripped a resistor off the PCB with a screwdriver trying to open up the sealed box. so i guess i will need both.

I definitely have VERY VERY VERY limited electronics knowledge (hence why I asked for help) but I still don't understand what is going on and would like to have an understanding. I have to at least learn from my mistakes

Why would antyhing cause me to be getting 4.x Volts (to battery ground) on the APPS sensor signal. This should be 0.5V at idle (to battery ground) according to the APPS reset article on dieseltrans.com. And I verified that when all was working last week.

Currently, if I take the APPS sensor ground and put it to a battery ground instead of using the ECM ground, , the APPS sensor signal goes back down to 0.5V and everything seems to be dandy. When hooked up to the APPS sensor ground to the ECM... 4V at idle, wont let me start the truck, etc.

What is going on there?

So what does the circuitry in the APPS do exactly? The potentiometer is just a linear potentiometer and it works whether the truck is on or off, no? Do the circuits provide the grounds perhaps???

the moral is the story is , if it's not broke don't fix it... and especially if you don't know what you're doing don't try to fix it. This is going to end up being a $500 high idle switch.

 

We've all been there, (the if it ain't broke part). In the grand scheme of things this will be no biggie. I know it's just nerve racking when you are trying to cover all the bases trouble shooting with no luck or end in sight.
It'll work out and we will all learn something at your expense, then a few weeks from now you'll save yourself the next potential headache on someone elses sad experiences.

Step back and take a deep breath.

Good Luck

 

"I think my ECM is screwed up regardless. i asked for a electrical engineer friend's help and he ripped a resistor off the PCB with a screwdriver trying to open up the sealed box. so i guess i will need both."

Can I have your old ECM ?

"Why would antyhing cause me to be getting 4.x Volts (to battery ground) on the APPS sensor signal. This should be 0.5V at idle (to battery ground) according to the APPS reset article on dieseltrans.com. And I verified that when all was working last week."

Can you share a link on that ?

I think the APPS is fried. Disconnect the APPS and do your measurements over. The ECM circuitry is pretty tough.


"Currently, if I take the APPS sensor ground and put it to a battery ground instead of using the ECM ground, the APPS sensor signal goes back down to 0.5V and everything seems to be dandy. When hooked up to the APPS sensor ground to the ECM... 4V at idle, wont let me start the truck, etc."

Can you run the truck with the APPS sensor ground connected to vehicle ground ?

"So what does the circuitry in the APPS do exactly? The potentiometer is just a linear potentiometer and it works whether the truck is on or off, no? Do the circuits provide the grounds perhaps???"

There are 2 pots in there, each with different outputs. This lets the ECM rationalize whether the pots are healthy or not, so it can detect a failed APPS. The circuitry has an op amp to control the ratio of the voltages between the two as well as the upper and lower bounds.

 

Sure.

http://www.dieseltrans.com/phpBB/viewtopic.php?t=614

I did the reset procedure just out of curiosity. It was in fact reading .3 V at idle whereas the tag on my APPS said it should be at .519. I did the adjustment and got it up to .51 V.

Well you have changed my mind. I think you are right too. Thanks for the insight.

Yes I can... It seems to run fine... Doesn't throw any codes either. Doesn't seem like it is the brightest idea though. From what you said below...

... there's probably a good reason for this... so my truck doesn't start going WOT when I am not telling it to, for example.

 

"Yes I can... It seems to run fine... Doesn't throw any codes either. Doesn't seem like it is the brightest idea though. From what you said below..."

Shorting the APPS to ground won't cause a run away truck. Apparently when you do that the APPS outputs are correct. As soon as the APPS outputs are incorrect, like when you leave the APPS ground float, the engine will be killed.

If it works shorted and you want to save a few bucks, just leave it shorted.

Can I still have your ECM ?

 

Don't sweat it, lots of us have done similiar things by accident(this will make you more careful from now on), besides APPS was probably on it's way out anyway . Maybe you should go ahead and fry your ecm , so you'll have reason to change it out with MAD ECM, you won't be disappointed.

 

I drove today... Just to move into the driveway. She is idling a WEE bit high. About 1000 RPM at .50 V instead of 800 or 850 or whatever. Not quite sure why. Wonder if this is something that is usually an "ECM learning" type thing (floor it slowly with the ignition on/engine off, and let off slowly as per the FSM). I wonder if the ECM isn't able to learn anymore because the APPS is all screwed up. If so I can probably make some mechanical adjustments to fix it.


I do plan on getting a new ECM but the truck is going to sit for a while. When I get the new one you can have it!