Engine/Transmission (1998.5 - 2002) I need help with modifying my high idle

[mgoncalves]

What I am attempting to do, is have the option of having my high idle kick in anytime the coolant is below the required 140 degrees. My friend is pretty handy with electronics, so he is doing most of this for me. It would be much easier for us if someone with a service manual can tell me a voltage value for a given temperature, or even a resistance value. The sensor I am messing with is the one under the drivers side battery.



So far, all we know is that as the temperature rises, so does the resistance of the sensor, which means as it gets hotter it lets less voltage through and vice versa. We will have to use a pot to find the right amount of resistance/voltage to use if there isn't a good range defined somewhere.



If anyone has the info, it would be greatly appreciated.



Thanks,

Matt

 

[Evan A. Beck]

Why are you focusing on the battery temperature sensor? Wouldn't it make more sense to go off the ECT (engine coolant temperatue) sensor? The battery temperature sensor is one of the inputs used for the charging system.



On another note, Banks has a device called a CBC (computerized brake controller) with their exhaust brake, which ties into the ECT sensor. It will activate the brake on a cold start, and keep it on until the temperate reaches 125°F. I am sure you could adapt it to make it work with a high idler instead of an exhaust brake.

 

[Whitmore]

Matt, the temp senser under the drivers side battery is for when the battery is charging , it senses the heat in the battery and will cut out the charging cycle if the battery is getting too hot



cheers, Kevin

 

[mgoncalves]

Well, I guess I am attacking the wrong place???



Evan: It is my undertstanding that the requirements for the factory high idle to go on are (other than parking brake, no throttle, etc. ) ambient temp below 32 degrees and coolant temp below 140 degrees.



Kevin: In another thread about the high idle, I asked which sensor was used to determine the ambient temp and was told it was the sensor under the battery. It was said that the intake manifold sensor wouldn't be able to get cold enough with the engine running and the grid heaters on. I didn't know where to start, so that answer sounded reasonable to me.





So does anyone know for sure which sensor is used for ambient air temperature?





By the way, what spurred this on is I love the high idle but wish it came on under about 50 degrees.



Thanks,

Matt

 

[Whitmore]

Matt,



The engine coolant temp senser located into the cooling jacket , at key on the PCM sends out a regulated 5 volt signal to the ETC senser, The PCM then monitors the signal as it passes thru the ETC senser to the senser ground or senser return. When the engine is cold the PCM will operate in loop cycle. It will demand slightly richer air/fuel mixture and higher idle speeds. This is done until normal operating temps are reached.



The PCM uses inputs from ETC senser for the following calculations.

injector pulse width

ASD relay shut down times

idle air control

pulse width prime shot during cranking

o2 senser closed loop times

purge solinoid on/off times

radiator fan operations

target idle speeds



cheers, Kevin

 

[mgoncalves]

That's kind of why I don't want to mess with the coolant temp sensor. I just want to be able to run the factory high idle anytime the coolant temp is under the 140 degrees as required by the computer. I should be able to give a false ambient air temp reading and as long as all the other requirements are met the high idle will be activated. I don't want to use the high idle if the engine is already fairly warm (140).



What I need to know is where does the signal for ambient temperature come from. If not the from the sensor under the battery or in the intake, where is it? It can't be the sensor for the overhead thermometer/compass, can it?





Thanks,

Matt

 

[Whitmore]

Matt, the IAT is at the drivers side far back on the motor in the intake, its near the MAP senser and it has 2 wires that go to the ECM where all the math is calculated.



cheers, Kevin

 

[mgoncalves]

Kevin,



Are you saying that the computer uses the IAT for its ambient reading? Do you have a list of what that sensor's results effect?







Thanks for your patience with me





Matt

 

[Whitmore]

Matt the IAT senser reads the temp inside the intake not ambient,



I have a temp senser in my intake horn and a gauge in the cab, I see aprox 20* higher than ambient at this point, now with the mass of the iorn at the location of the IAT I am guessing yet another 20-30*



so ambient being say 40*

intake horn at 60*

IAT at 80-90*



This summer I will get more readings at the horn and I am still looking for 20* above ambient... ... ... ... unless heavy load and then all bets are off.



90* intake * is desired for max efficiency.



cheers, Kevin

 

[Evan A. Beck]

Originally posted by Whitmore



The PCM uses inputs from ETC senser for the following calculations.

injector pulse width

ASD relay shut down times

idle air control

pulse width prime shot during cranking

o2 senser closed loop times

purge solinoid on/off times

radiator fan operations

target idle speeds

Kevin,



I think your findings about the ECT sensor are for a gas powered truck, not a diesel... O2 sensor, inj PW, etc...

 

[mgoncalves]

That's what I understood, the IAT does not supply the ambient reading. It would be to hot in the intake to be less than 30 degrees for very long.



OK, now I am getting real confused. If the IAT sensor doesn't supply the computer with this, and the battery temp sensor doesn't do it, what does??



Everything points at the sensor under the battery. That is the only logical sensor to supply an ambient reading. Will I hurt anything by telling the computer that the battery is colder than it really is on occasion?



Well, I'll find out tomorrow if the battery sensor is tied in with the high idle



Thanks,

Matt

 

[mgoncalves]

So, does anyone know what voltage is required for the temp. to be below 30 degrees and also one for below 15 degrees?