Sense the IAT sensor needs to put out a certain resistance value to trigger the 3cyl High Idle. Is there a way to fool the sensor with some resistors to make the computer think it is 15deg or whatever. Maybe put this on a switch to activate it with a warning light to shut it off when you start driving?

Anyone done this? Diagrams? Pictures?

Thanks

 

i saw on another site a guy did that...cost like25$ in parts from radio shack, he had a writeup with pics and wiring diagram. my brother and i are kinda in the process of seeing if we cant get it worked out on ours...

 

I think you need to fool the coolant temp sensor too, maybe the battery temp as well. It's not as easy a just one sensor, I do know that.

And yes you can use a resistor and a switch for fooling IAT, many people are doing it now for timing purposes.

 

https://www.dieseltruckresource.com/...d.php?t=136583

 

Coolant temp would be that low. I am talking for like a 35deg start in the morn. There is no Battery Temp Sensor as it relates to the high idle feature.

 

Thanks for the link. Good information but it seems overly complicated to do a potenceomnetor. I want to see a diagram to hook up so the CPU sees like 10 deg at the flip of a switch then when turned off normal operation happens. Make sense?

 

If you don't want to use a potentiometer, just use a fixed resistance (may take some experimenting to find the right size) and add it in series with the IAT sensor. ie, cut one wire to the IAT sensor and add the resistor to the circuit between the two ends of wires. In order to bypass it when not needed, you need a switch installed that also needs connected to those same two ends of wires.

When the switch is open, the resistance is added, ECM will see very cold temps. When the switch is closed, no resistance is added, ECM will see normal temps.

My reason to want the 3 cyl idle would be on those mornings that the truck has been plugged in all night so coolant temp is somewhat warm. The 3 cyl idle would just speed up the rate at which it came up to temp, however this requires fooling of the coolant temp sensor as well.

 

I can see where you are coming from on the coolant sensor.


So I would jump the two wires and bring the power wire in to the switch and on the out part of swtich add the resistors and wire into the out part of the sensor. So it would see at least the minimum resistance needed to activate 3cyl Idle. Kind of like stacking it on top of IAT resistance's, if I am thinking correctly.

 

Here's a picture of what I'm talking about. I would try a 50k ohm resistor to start. That should be enough to fool the ECM into thinking the air temp is cold enough for high idle and 3 cyl idle.

Just remember to open the switch before you drive away or the ECM will still think it's zero out and have advanced the timing.

 

Thanks for all your help, still trying to understand here. I would add a light like my low fuel pressure light to tell me when its active. Doesn't the break for the switch need to be before the resistor so its not there all the time? I dont understand from your drawing where the break is. See attached for what my mind thinking.

 

It will always take the path of least resistance... In your markup, even with the switch closed, the ECM won't see your resistor because the path of least resistance wouldn't be thru your resistor.

In my example, with the switch closed, the circuit would go thru the switch (no resistance) and not see the added resistor.

Maybe I'm just confusing you more?

That's a good idea for having a light to remind you that it's on. You could use a dual pole dual throw switch that would light up when turned on. I posted a picture of some in my Excursion cummins swap link. Click on my sig and go to the last page (11 maybe), there's a picture of some switches I got from waytekwire.com.

 

I think I got it. With the switch closed it becomes the path of least resistance bypassing the resistor even tho it is still inline, with switch open it has to go thru the resistor. Would it be easier to use a lighted switch or switch with a warning light?

 

Either way would work, you just don't want to wire any of your 12V signal or ground for the light into the IAT circuit (keep it separate).

 

Right because a DPDT switch will activate two circuits. It is making sense to me now . Thanks for the patience. I am an I.T. person not an electrical enginneer.