APCM/AIC High Idle Mod
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Laughing Gas
Joined: Aug 2008
Posts: 823
Likes: 5
From: Dallas, Oregon
APCM/AIC High Idle Mod
I have searched the forums for information on this mod. There are some good posts on how to hook up a high idle control to the TPS (accelerator pedal), but I was wondering if anyone had done a setup using the factory APCM harness.
The factory harness has 4 wires: black-ground. red/yellow-switched power. pink/light blue-pcm/OBDII --. tan/orange-pcm/OBDII +. As best I can tell, the switched power and ground wires are for controlling an electrically actuated PTO. The other two wires connect directly to the PCM and I am guessing that they are the RPM control. If an OBDII diagnostic module can control RPM from the port, the same mechanism should do it from the two wires in the APCM wiring harness.
Does anyone know how the diagnostic tool controls RPM? I would expect that a variable resistance would work if it is analog, but a more sophisticated device would be necessary if it were digital. Does anyone know if there is a risk of doing damage by putting a pot accross the two control wires to test?
Thanks,
The factory harness has 4 wires: black-ground. red/yellow-switched power. pink/light blue-pcm/OBDII --. tan/orange-pcm/OBDII +. As best I can tell, the switched power and ground wires are for controlling an electrically actuated PTO. The other two wires connect directly to the PCM and I am guessing that they are the RPM control. If an OBDII diagnostic module can control RPM from the port, the same mechanism should do it from the two wires in the APCM wiring harness.
Does anyone know how the diagnostic tool controls RPM? I would expect that a variable resistance would work if it is analog, but a more sophisticated device would be necessary if it were digital. Does anyone know if there is a risk of doing damage by putting a pot accross the two control wires to test?
Thanks,
Lead Driver
Joined: Jun 2003
Posts: 8,298
Likes: 25
From: Damon (South East Texas)
I have searched the forums for information on this mod. There are some good posts on how to hook up a high idle control to the TPS (accelerator pedal), but I was wondering if anyone had done a setup using the factory APCM harness.
The factory harness has 4 wires: black-ground. red/yellow-switched power. pink/light blue-pcm/OBDII --. tan/orange-pcm/OBDII +. As best I can tell, the switched power and ground wires are for controlling an electrically actuated PTO. The other two wires connect directly to the PCM and I am guessing that they are the RPM control. If an OBDII diagnostic module can control RPM from the port, the same mechanism should do it from the two wires in the APCM wiring harness.
Does anyone know how the diagnostic tool controls RPM? I would expect that a variable resistance would work if it is analog, but a more sophisticated device would be necessary if it were digital. Does anyone know if there is a risk of doing damage by putting a pot accross the two control wires to test?
Thanks,
The factory harness has 4 wires: black-ground. red/yellow-switched power. pink/light blue-pcm/OBDII --. tan/orange-pcm/OBDII +. As best I can tell, the switched power and ground wires are for controlling an electrically actuated PTO. The other two wires connect directly to the PCM and I am guessing that they are the RPM control. If an OBDII diagnostic module can control RPM from the port, the same mechanism should do it from the two wires in the APCM wiring harness.
Does anyone know how the diagnostic tool controls RPM? I would expect that a variable resistance would work if it is analog, but a more sophisticated device would be necessary if it were digital. Does anyone know if there is a risk of doing damage by putting a pot accross the two control wires to test?
Thanks,
since then and don't remember the details.
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Laughing Gas
Joined: Aug 2008
Posts: 823
Likes: 5
From: Dallas, Oregon
Thanks Roland. I have done more reading since and think I am brave enough to put a rheostat between the two PCM/OBDII wires. I have not found any information on what they do on the earlier trucks, but the 08 information I have found looks like among the many circuits they have added, there are still the two + and - wires to control engine speed with a rheostat. The only joker will be if I need 12V power somewhere to trick the PCM into thinking that a PTO is engaged, but I have not found that input in the connector wiring diagram.
If this works, it will be great because it will use existing wiring and I won't need to cut the wires to the "gas" pedal.
If this works, it will be great because it will use existing wiring and I won't need to cut the wires to the "gas" pedal.
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mfp4073
1983 - 2012 Ranger & B-Series
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Jun 17, 2014 02:38 PM
