Originally Posted by crobtex

I think it goes like this:

1st Gen = 12 valve
2nd Gen = 24 valve with electronics (98.5 to 2002)
3rd Gen = 24 valve with Common Rail fuel system (CP3)

Originally Posted by tool

Ummm....... Not sure I understand this theory, maybe the PCM does not use this the data but the ECM sure does. WIthout proper APPS signal voltage the ECM cannot judge how much throttle is being applied via the foot feed and does not know how much fueling to provide.

I think the second procedure is very worthwhile for manual tranny trucks, just as others have experienced.

Originally Posted by rjohnson

2fun - Slight correction!

1st, 2nd & 3rd Gens were body style changes.

-All 1st gens were 12v.
-2nd Gens were 12v through mid 98. 98.5's and up are 24v.
-All 3rd Gen's are 24v's w/ common rail injection.

RJ

Originally Posted by pc12driver

Of course the ECM uses APPS info. Since we're drive-by-wire, that's the only way throttle info gets to the engine. I never said it didn't.

"Proper APPS signal voltage": There is not a set minimum or maximum voltage that the ECM looks for. It self-learns those values when the batteries are reconnected and the throttle is depressed to the floor the first time. When you re-clock the APPS, you're linearly raising or lowering the voltages that the ECM sees, at which point it will relearn the new values (after a couple of cycles or a battery disconnect/reconnect) and you'll be right back to where you started. You could pretty much reclock the APPS to any voltage you wanted and the ECM will readjust itself to the new minimum and maximum values, and the truck will drive exactly the same as it did before the reclock (not counting shift points on an auto).

The PCM doesn't automatically adjust, and needs the voltage from the APPS tuned to match it's needs. It's probably a RPM vs. throttle position equation that determines load on the transmission, and if the PCM "sees" more or less throttle than what actually exists, then the TC lock/unlock schedule or tranny shifting schedule will be thrown off. So the APPS needs to be reclocked or "tuned" so the PCM sees a known idle throttle position voltage, and then the ECM will automatically relearn the new voltages. This puts the engine and the tranny on the same page so they can work together.

Long story short: On a manual tranny truck, only the ECM needs APPS info, not the PCM. And since the ECM automatically adjusts for voltage variances, there's no need to reclock the APPS. Not a theory - that's how it works. If you want to reclock the APPS on your manual tranny truck, go ahead, it won't hurt anything. It just won't accomplish anything either. For automatics, go ahead and adjust it. You might pick up some economy and decrease some tranny wear.

Tool (or anyone else), if you can give a better explanation as to why the second method would actually do something on a manual truck, please share.

Originally Posted by 2fun

..Another Q though.... What exactly do you mean when you say "common rail"??? I am not familiar with this term?? Thanks!

Originally Posted by crobtex

Here is the adjust procedure, it is not the same as the reset:

RESETTING THE APPS SENSOR.
(ACCELERATOR PEDAL POSITION SENSOR)
2ND GENERATION 24 VALVE TRUCKS ONLY.

LIST OF TOOLS NEEDED

DIGITAL VOLT METER
# 20 TORQUE BIT SOCKET
# 1 PHILLIPS
# 10 MM SOCKET

Proper service and repair procedures are vital to ensure personal safety of those performing the repairs. Standard safety procedures and precautions should be followed at all times to eliminate the personal injury or improper service, which could damage the vehicle or compromise its safety.
Although this material has been prepared with the intent to provide reliable information, no liability is assumed in reliance of this material.

It has come to my attention that a lot of people think by disconnecting & re-connecting the batteries and stepping on the throttle it is going to reset the apps, no, that is not correct. It is impossible to adjust your apps if you do not know where it is supposed to be set at. That is why you need the voltmeter.

This is the procedure I use to re-set the apps.

With the key on, engine off you need to probe the apps wire to see where your voltage is currently set at.
The best location to probe the wire is on the PCM (power control module) which is located off the passenger side of the firewall.

· You want the C1 connector, this is the connector closest to the engine,
· You want the orange wire with the dark blue tracer which is pin # 23
· Voltage should read somewhere around 0.5 volts,
· At this point the voltage reading does not matter, it just has to be accurately written down for later reference.

*** TURN THE IGNITION OFF ON THE TRUCK ***




Resetting the APPS Sensor cont. page 2
(Accelerator Pedal Position Sensor)
2nd generation 24 valve trucks only.

· The apps sensor is located slightly above and a little to the left of the injection pump.

· Remove the black plastic cover that is located by your injection pump.

The two screws that are holding it are plastic, do not put any downward pressure on them or you will never get them off.

· Un do the 6 - 10 mm headed bolts that hold the bracketry in place.
(DO NOT REMOVE THE CABLES)

You will notice the apps is on the back of the bracketry that you just removed, it is held in place by 2 - 20 bit screws. These screws have a little bit of locktite on them so make sure you have a good socket and gently give a little tap with a hammer before attempting to loosen. Be very careful these screws strip very easily and you only get one shot at them.

· On the apps you will find a white tag that gives you the information on what the apps adjustment should be.

· After loosening the screws you can rotate the apps both clockwise and counter clockwise to get the adjustment you need.

· The reading you took at the beginning of the process on pin # 23 should match the white tag on your apps, if not adjust accordingly.

Originally Posted by TNfarmboy

Very interesting read. I tried the battery disconnect procedure once just for the heck of it , not that I had any symptoms, and didn't notice anything. I once asked why my truck idles so high (900rpm) compared to my 12v which is like a gas engine and about 650 to 700....never got a good answer just some stuff about a high idle kit . Makes me wonder if I should check my idle voltage and try lowering it....(wonder). Maybe I will just leave it alone

Originally Posted by rjohnson

Sorry,,, just saw this post.
Common rail is the fuel delivery system on all 3rd gens. Fuel pump pressurizes common reservoir (Rail) from which the injectors are fed.
2nd gens have individual fuel lines from the fuel pump to each injector.

RJ

Originally Posted by rjohnson

2fun - Slight correction!

1st, 2nd & 3rd Gens were body style changes.

-All 1st gens were 12v.
-2nd Gens were 12v through mid 98. 98.5's and up are 24v.
-All 3rd Gen's are 24v's w/ common rail injection.

RJ