DIY AIC
Senior User
Joined: Aug 2010
Posts: 238
Likes: 0
I just got done making the 'pigtails for the relays for this mod.
The way that mod works, the "new" pot takes the place of "half" of the APS's resistor and uses the "fixed value" (of the APS) that remains. When activated, twisting the **** has the same effect as depressing the pedal.
The APS is nominally a 5K resistor and it is supplied with a 5VDC reference. The wiper is connected to the ECU and the other leg is grounded. With the IVS closed, the ECU reads the voltage at the wiper. The more the pedal is depressed, the higher the voltage the ECU sees.
If you want a larger range of RPM adjustment, go with a little larger (resistance) pot. I wouldn't go any larger than 5K.
The way that mod works, the "new" pot takes the place of "half" of the APS's resistor and uses the "fixed value" (of the APS) that remains. When activated, twisting the **** has the same effect as depressing the pedal.
The APS is nominally a 5K resistor and it is supplied with a 5VDC reference. The wiper is connected to the ECU and the other leg is grounded. With the IVS closed, the ECU reads the voltage at the wiper. The more the pedal is depressed, the higher the voltage the ECU sees.
If you want a larger range of RPM adjustment, go with a little larger (resistance) pot. I wouldn't go any larger than 5K.
Thread Starter
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Logistics Pro
Joined: Oct 2008
Posts: 4,818
Likes: 1
From: Avilla, IN
First off, 0 ohms is no resistance and that is a dead short.
If the pcm supplies 5V, then the voltage drop across the circuit must also be 5V. This is Kirchoff's Voltage Law. This means the the pcm can only determine the current through said circuit. The Current equals Voltage divided by Resistance.
The directions indictate that as you turn the pot counter-clockwise you reach maximum resistance. 2 kOhms in this case. Later it says that turning the pot clockwise (reducing resistance) will increase rpm. Another user here did this mod and reported an effective range of 1200 rpm to 2500 rpm. Since I already determined from the instructions that you turn the pot clockwise to increase rpm and decrease resistance. If you assume that its a linear system you can make a model for the pot resistance compared to rpm. I did this and determined that to move the rpm range from 1200-2500 to 700-2000, I need 750 Ohms in series with the pot.
If you are curious, the equation is:
RPM = (-13/20)*(Pot Resistance + Added Resistor Value) + 2500
If the pcm supplies 5V, then the voltage drop across the circuit must also be 5V. This is Kirchoff's Voltage Law. This means the the pcm can only determine the current through said circuit. The Current equals Voltage divided by Resistance.
The directions indictate that as you turn the pot counter-clockwise you reach maximum resistance. 2 kOhms in this case. Later it says that turning the pot clockwise (reducing resistance) will increase rpm. Another user here did this mod and reported an effective range of 1200 rpm to 2500 rpm. Since I already determined from the instructions that you turn the pot clockwise to increase rpm and decrease resistance. If you assume that its a linear system you can make a model for the pot resistance compared to rpm. I did this and determined that to move the rpm range from 1200-2500 to 700-2000, I need 750 Ohms in series with the pot.
If you are curious, the equation is:
RPM = (-13/20)*(Pot Resistance + Added Resistor Value) + 2500
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
Just ordered the parts to do my own. Got everything from DigiKey.com plus a handful of 75k ohm resistors for the 140V IDM Mod for less than $30. Even ordered a nice aluminum **** to put on the Potentiometer. Too bad everything isn't here for this long weekend.
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
I just finished installing the DIY AIC mod and it works well, however I can't adjust the idle below about 1500 RPMs once the engine starts to warm up. I may need to add a bit more resistance to the circuit. Other than that it works like a charm. I'll be sure and update what I find.
Hotshot
Joined: Oct 2003
Posts: 17,791
Likes: 99
From: Ashland City, TN
Redneck AIC
Go to the hardware, pick up a broomstick.
Use the new broomstick to replace the broken and mended one in the garage.
Take the one that's broke and cut to adjust.
Wedge between seat and pedal.
Done.
hahahaha. =)
Go to the hardware, pick up a broomstick.
Use the new broomstick to replace the broken and mended one in the garage.
Take the one that's broke and cut to adjust.
Wedge between seat and pedal.
Done.
hahahaha. =)
Thread Starter
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Logistics Pro
Joined: Oct 2008
Posts: 4,818
Likes: 1
From: Avilla, IN
I am going to try and get mine done tomorrow night. I've been so busy lately I haven't gotten around to putting all the pieces together.
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From: Illinois
Post Fiend
Joined: Dec 2010
Posts: 10,121
Likes: 3
From: Orrville, Ohio
I don't know what has made the difference but I haven't had the issue of not being able to adjust the idle down on a warm engine since the first time I used the AIC. It seems to work fine now on a cold or a warm engine. The only thing that takes a little tweaking is that as the engine warms up it runs progressively faster and faster. I still think this is a function of the PCM changing the injector timing but it works fine as long as I sit there for a minute or so and slowly adjust the idle back down until it stabilizes. I really like this for warming up a cold truck on mornings like this one when it is in the single digits outside. Combine this with plugging in the block heater and it really warms up fast. This is a really good mod for the $30 or so it costs. No regrets so far. I will have to take a picture later of the finished product of where and how I mounted the switch and pot.
Cargo Master
Joined: Oct 2010
Posts: 2,674
Likes: 16
From: Ideeho
I did that for quite a few years on my 96 F350. I finally found the Ford AIC on ebay and installed it. I love it. The only thing I dont like about it is the mounting. I'm thinking the bracket that came with mine is for a SuperDuty. Does anyone have a pic of the Ford AIC mounted correctly in a 96 with a 5 speed? Thanks.....
