Engine/Transmission (1994 - 1998) How about a fixed value resistor in place of the IAT sensor?

[Fordiesel69]

Instead of having the heater grids come one when the PCM feel it is necessary, is it possible to place a resistor on the connector so the heater will always come on?



I don;t like the smoke issue when you let the truck sit for 2-4 hours and the intake is still warm enough to not let them come on.



Anyone have a resistence table relating temp vs ohms?

 

[tgordon]

Here you go. Most people are going the other direction, getting rid of them.



Hope this works for you and is legible.

 

[EKlem]

Yes, it is possible. If you want them to run for 30 seconds, you can just unplug the IAT sensor. If you want them to run for 10 or 20 seconds, the table that tgordon posted will allow you to do that.

One thing to keep in mind is that if you do this, your grids will cycle as if it is really cold whenever you start the truck. This would not be ideal for driving in the summer since it really draws on your batteries.

I suppose you could put a variable resistor in there but then you might as well just rig up a manual switch at that point.

 

[Fordiesel69]

So would this work:



RadioShack.com - Cables, Parts & Connectors: Component parts: Capacitors & resistors: 47K Ohm 1/4-Watt Carbon Film Resistor (5-Pack)



this would put me in between 32 and 14 degrees F. I wonder how many seconds this would be? How long are the grids supposed to cycle after the engine is running, and do both of them cycle together?

 

[tp0d]

Well, since the IAT is -after- the grids, it senses the grids warming up the air, the resistance changes, and the computer turns off the relay for the grids. So, if you put a resistor in there to fool the PCM, the grids will never shut off, and could melt something down... not good.

Instead of changing the wiring as it currently is, just get a toggle switch and wire it onto the relays so you can manually control the grids. I was thinking about doing this at one time, but got side-tracked. I believe Dodge uses a switched ground system, so you would wire one end of the switch to ground and the other to the switching terminal on the relay (ie, the terminal that doesnt read power to gnd)

I would not recommend running the grids for more than 10secs at a time. Bad draw for the batts and for the alt. Could possibly melt something down if they got too hot, dunno. I`ve never heard mine kick on for more than 5secs at a time, got to be a reason for that.

good luck

-j

 

[Fordiesel69]

UPDATE, I installed a 47k ohm resistor and now I get a 10 sec preheat and about a 3 minute on off cycle if I just leave it idle. If I drive it will immediatly stop above 15 mph and not come back until the next start. No smoke on 2-4 hour starts either. 10 sec is all I have seen even when it was 11 degrees one night and the IAT sensor hooked up. Should they ever preheat 20-30 sec?

 

[EKlem]

With the IAT intact, they will heat up to 30 seconds when it gets really cold. If you are going to see colder temps than 11 degrees, I would think that you would want the grids to be able to run at least 20 seconds. You could accomplish this by cycling the key twice. You could also put in a different resistor and in warmer weather just start cranking after a few seconds even though the grids are still heating.