High idle mod
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i know in my brothers dodge (cummins) when he is in park, he can press the on button on the cruise control and then raise or lower his idle with the accelerate or coast buttons in increments of 100RPM all the way up to 1500. his is an 07.5 so everything is controlled by the ECM.
i know its a completely different animal, but there has got to be something
i know its a completely different animal, but there has got to be something
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im not really sure where voltage came into the conversation. the only reason you'd need to keep a alternator at a higher RPM as i described would be for amperage output. new alternator or not, no alternator is going to be able to keep up with the demands of a winch and having a second battery is just a really really gay bandaid. Warn's 12.5K winch at maximum load uses around 500-600amps. the goal is to be able to keep the alternator spinning where it makes most electricity so the battery replenishment is at its most efficient level. plus if im in a situation where i need a winch or excessive amounts of lights, fuel consumption is probably going to be last on my list
Last edited by marshal; 12-16-2010 at 10:34 AM.
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There are a couple high rpm strategies used by the PCM. Cold Idle start up, low voltage, extended idle, AC performance, and alternator high field conditions. If you want to use the PCM to control, you need to trick one of these signals. AC head pressure would work, but would also would trip the high speed fans and suck 40+ amps.
Extended Idle, low voltage and alternator high field idle kicks are probably not high enough to be worth the trouble. Extended Idle simply raises idle rpm if idling for a length of time, most vehicles around 20 minutes. That is PCM internal timing, good luck on modifying that. Low Voltage is used by both the PCM and alternator for control and feedback. There are 3 - 4 power input lines into the PCM, trying to figure out which one the PCM uses to determine low voltage issues would be an interesting task. If a low voltage is determined, engine idle is raised but not to an unlimited amount. This will cause a "Check Charging System" DTC though if playing with the voltage values. But can be cleared pretty easily.
The PCM and alternator communicate in PWM signals. If the alternator tells the PCM it is in full field, the PCM will begin to raise the idle rpm after a set time if condition still exists. Making an interface to control this signal would be more work then simply adding a second alternator to the system.
All of these idle rpm increases are not that much, likely 850 rpm at the most, it depends on the particular engine calibration and likely differs between each engine option. The highest engine kick would come from cold idle conditions.
Cold Idle start works off the ambient sensor & ECT, but playing with this affects engine timing and performance. No biggie during idle only, clearing DTC's would be easy. But would need to interface the two sensors. Other than that, I don't know of any other way to increase idle rpm except one.
If you want my honest opinion. Have somebody press on the gas pedal...
Extended Idle, low voltage and alternator high field idle kicks are probably not high enough to be worth the trouble. Extended Idle simply raises idle rpm if idling for a length of time, most vehicles around 20 minutes. That is PCM internal timing, good luck on modifying that. Low Voltage is used by both the PCM and alternator for control and feedback. There are 3 - 4 power input lines into the PCM, trying to figure out which one the PCM uses to determine low voltage issues would be an interesting task. If a low voltage is determined, engine idle is raised but not to an unlimited amount. This will cause a "Check Charging System" DTC though if playing with the voltage values. But can be cleared pretty easily.
The PCM and alternator communicate in PWM signals. If the alternator tells the PCM it is in full field, the PCM will begin to raise the idle rpm after a set time if condition still exists. Making an interface to control this signal would be more work then simply adding a second alternator to the system.
All of these idle rpm increases are not that much, likely 850 rpm at the most, it depends on the particular engine calibration and likely differs between each engine option. The highest engine kick would come from cold idle conditions.
Cold Idle start works off the ambient sensor & ECT, but playing with this affects engine timing and performance. No biggie during idle only, clearing DTC's would be easy. But would need to interface the two sensors. Other than that, I don't know of any other way to increase idle rpm except one.
If you want my honest opinion. Have somebody press on the gas pedal...
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Now I see where you're going with this. That makes sense now! I think it would be nice to be able to keep some accessories going without killing the battery. I only had one set of offroad lights on my F250 so they didn't draw much. I mostly did it for cold weather to keep the motor warm.
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If you could find the wire and value the gas pedal sensor is sending the PCM you could modify that signal. It was built in my 05 F250 I just soldered two wires together to use the BCP idle which was a 1200rpm base and monitored battery charge. It makes the A/C kick a lot harder down here in Texas. My A/C barely trickles cold at idle...
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