Engine/Transmission (1998.5 - 2002) APPS Calibration for mileage?

[Bunyan]

does calibrating your apps give you better mileage?

 

[Bob4x4]

No... ... ... .

 

[blacksheepdiesel]

Uhmm, actually, if the APPS is not within specs it can effect mileage. Also, if an APPS is getting worn it can have a negative effect on fuel mileage. The reason is because the tracer tracks get worn and when you have the cruise control set the speed will go down 1 mile below what the cruise is set at and then it gives the engine extra fuel to get back up to the set point. Continual seesawing will decrease mileage, even if a little bit as it is more efficient to run a constant speed. I have had 4 or 5 different APPS on my truck and every one of them has done this toward the end of it's life cycle, which isn't very long when you drive at one speed all the time. The last APPS I took off was a new from Dodge unit that only lasted 50,000 miles and never did give me good mpg's. I currently have one of Gary's microswitch units on it and it gives noticeably better mpg's than the previous one. The engine even sounds smoother. I have an APPS from timbo on standby when this one dies and I will have to calibrate it.

A correctly calibrated APPS will make the engine run smoother and more efficiently than an out of spec APPS.

Godspeed,
Trent

 

[Jefff929]

Trent, excellent answer

Bunyan, I think Bob4x4 was basically correct in that if it is a little off you are probably not going to notice the change, so no not directly. When I calibrated my APPS I found it slightly changed the shift points on the trany for the better, that could affect the mpg.

 

[Bunyan]

thanks guys. Bunyan

 

[PC12Driver]

A correctly calibrated APPS will make the engine run smoother and more efficiently than an out of spec APPS.

I can see a new APPS producing those results over an old APPS with dirty or worn brushes, but I don't see how adjusting the voltage will change how the engine runs. The ECM translates the output voltage of the APPS to a desired RPM - nothing more. And the ECM self-adjusts for the voltage range of the APPS.



So let's say that you're tag says . 550v and your actual reading is . 500v. According to the "calibration" procedures, you advance the APPS rehostat body so the actual volts match the tag at idle. You've simply moved the brushes further down the plate by a degree or so. Effectively the same thing as depressing the throttle pedal a touch. And Pushing on the pedal a little bit won't make the engine run any better, just a little faster.



After reclocking the APPS rehostat, the ECM needs to learn the new minimum and maximum voltages from the APPS so it can assign them to idle and full throttle, respectively (disconnect/reconnect batteries, key on, pedal slowly to floor and back to idle). Before the APPS adjust, 1. 00v might have resulted in 1,500 rpm no-load (made up numbers just for example). Now, after reclocking and re-teaching the ECM, 1. 05v would give 1,500 rpm. Engine-wise, that is the only thing that has changed. Timing and fueling are based on intake temperature and pressure, and engine load. The APPS voltage/rpm relationship is irrelivant to engine performance.



Where this can help however, is the case where the few degrees of twist might put you past a bad spot on the brushes. Since the bad spot usually happens at 1,800 +/- rpm though, getting past the bad spot is unlikely. The folks most likely to benefit from the adjustment are the auto trans guys, since adjusting the volts to match will get the auto transmission shifting to match the engine load more precisely (like Jeff).



As an example of how the voltages don't effect the manual transmission trucks, I replaced my factory APPS (. 520-ish) with a Williams Controlls APPS (. 640v) and didn't notice a thing (aside from the missing dead spot). If idle voltage was worth anything more to the ECM than an RPM command, I would have surely noticed something with that big of a jump.

 

[Bob4x4]

Uhmm, actually, if the APPS is not within specs it can effect mileage. Also, if an APPS is getting worn it can have a negative effect on fuel mileage. The reason is because the tracer tracks get worn and when you have the cruise control set the speed will go down 1 mile below what the cruise is set at and then it gives the engine extra fuel to get back up to the set point. Continual seesawing will decrease mileage, even if a little bit as it is more efficient to run a constant speed. I have had 4 or 5 different APPS on my truck and every one of them has done this toward the end of it's life cycle, which isn't very long when you drive at one speed all the time. The last APPS I took off was a new from Dodge unit that only lasted 50,000 miles and never did give me good mpg's. I currently have one of Gary's microswitch units on it and it gives noticeably better mpg's than the previous one. The engine even sounds smoother. I have an APPS from timbo on standby when this one dies and I will have to calibrate it.



A correctly calibrated APPS will make the engine run smoother and more efficiently than an out of spec APPS.



Godspeed,

Trent

:-laf:-laf:-laf:-laf

 

[blacksheepdiesel]

No ******* match here, guys! I am no electronics guru but I do have 500,000+ miles experience driving and wrenching on one truck. My tendency is to be very observant of everything, including how the truck is operating and therefore I notice even the slightest changes. I can't prove by scientific tests that a correctly calibrated APPS makes the engine run better or provide better MPG's but I do know what my experience has been.

Is it possible to see the real time output of the APPS? I know there are some incredible electronic tools these days. It would be fascinating and enlightening to see what the APPS is doing while driving down the road. I would be willing to donate my truck and my time to one day's worth of tests with several different APPS being installed, calibrated and not, brand new and worn, Dodge and Williams, and see what effect if any it may have on engine performance and mpg's. Since I travel all over the country the location of testing is not an issue for me. Anybody up for it?

When buying a new APPS from Dodge I was told that breaking the seal to calibrate the APPS would void the one year warranty, so I didn't touch it. It is possible that some of those brand new factory fresh APPS I received were not the best internally which could be the cause for lower mpg's and engine not running as smooth as it has. That most certainly could be the case for my last Dodge APPS as it only lasted 50,000 miles instead of the normal 100,000.

I do know that the APPS was one of the main causes in breaking two NV5600 transmission's in my truck. Both times I had heavy 5th wheel campers hitched up to a 5th wheel hitch that had a lot of slop in it. The ring and pinion was also worn and had a lot of play there. With the cruise control set at 65 mph and going up a slight but moderately long grade in both instances the cruise control dropped out and then it realized the truck was losing speed and so it applied full throttle. The engine sped up, then the slop was taken up in the ring and pinion and finally the play in the hitch was tightened up and "WHAM". It broke three teeth off of 6th gear at the root and the 2nd time it broke a brand new mainshaft. About a month after the 2nd transmission was replaced I began to notice the APPS was acting up and soon installed a new one. The ecm was simply more sensitive to the APPS than I was. New APPS, no more broken transmission's! The 5th wheel hitch was eventually replaced also.

Again, I am not an expert but I do have a lot of experience with one truck.

Godspeed,
Trent

 

[PC12Driver]

As it turns out, I have a bunch of miles on my truck and am quite perceptive of its performance as well. I've had three APPS on my truck, and aside from the failures that were fixed (dead pedal, fluttering RPM), I did not notice any change in performance. I do notice however that it runs smoother when I drive it right after I run my Kubota tractor. But then it does feel a little rough after I fly the turbine-powered plane. My point being that the seat-of-the-pants-meter is relative, biased, and inaccurate. We all know someone who swears an oil change improves power. SOP feel is irrelevant.



There's nothing scientific or magic about the APPS. It's just like a volume knob on a radio, or a variable resistor, nothing more. The idle position has the most resistance, full throttle the least. Less resistance = more volts. And all the available APPS make the same flavor volts, so the ECM won't prefer one over the other. Volts are directly proportional to the RPM. So a direct indication of what the APPS is doing on the road is the tach. No special tools needed.



You're giving that little volume knob too much credit for things it has no control over.



BTW, your truck has a vacuum controlled cruise control (two cables to the APPS)? According to my shop manual, all the manual trucks run cruise electronically... . ?

 

[Bob4x4]

I would never tow a heavy load with cruise... ... ... what were you thinking????

 

[Jefff929]

how heavy is heavy?

 

[blacksheepdiesel]

Yep, vacuum cruise, early 2001 model with NV5600. I thought the vacuum cruise was used until mid-year when the rear drum brakes were replaced with disc brakes??

Bob, when I drive in SoCal I DEFINITELY don't use the cruise because of mountains and wwwaayyyyy too many people!!!! Have towed almost 300,000 miles with cruise set.

Jeff, a couple months ago I pulled a Newmar Kountry Aire 5th wheel (supposedly the last one made) from Indianapolis to NJ. Newmar makes the only campers I know of with dual-tandem axles (8 tires) which have a GVW of 21,000 lbs!! This particular camper also had a custom tile floor and my guess is it weighed between 16k and 17k and my truck weighs 9k; fortunately I didn't have to cross any weigh station scales, they were all closed!!!! I would much rather pull this camper than a 29' bumper hitch "tail wagger" any day. Most of the time the loads I pull range from 6k to 12k.

Godspeed,
Trent

 

[HBarlow]

As it turns out, I have a bunch of miles on my truck and am quite perceptive of its performance as well. I've had three APPS on my truck, and aside from the failures that were fixed (dead pedal, fluttering RPM), I did not notice any change in performance. I do notice however that it runs smoother when I drive it right after I run my Kubota tractor. But then it does feel a little rough after I fly the turbine-powered plane. My point being that the seat-of-the-pants-meter is relative, biased, and inaccurate. We all know someone who swears an oil change improves power. SOP feel is irrelevant.

There's nothing scientific or magic about the APPS. It's just like a volume knob on a radio, or a variable resistor, nothing more. The idle position has the most resistance, full throttle the least. Less resistance = more volts. And all the available APPS make the same flavor volts, so the ECM won't prefer one over the other. Volts are directly proportional to the RPM. So a direct indication of what the APPS is doing on the road is the tach. No special tools needed.

You're giving that little volume knob too much credit for things it has no control over.

BTW, your truck has a vacuum controlled cruise control (two cables to the APPS)? According to my shop manual, all the manual trucks run cruise electronically... . ?

Ditto. Well said.

It is, unfortunately, somewhat rare to read common sense posts like this.

I find it surprising and disappointing to read so many posts by folks who fervently believe that snake oil in their crankcase makes 20% more horsepower, 30% more torque, and an additional 10 mpg or some new aftermarket part like a new dipstick with a chrome handle makes the engine run smoother or faster.

I replaced the APPS in my high mileage '01 so many times I was afraid I'd wear out the threads in the mount and never notices any difference whatsoever in performance or fuel economy with new ones, old ones, or just broken in APPS modules. If Gary had been offering his improved versions then I would have been first inline to buy one.