Heater Grids and IAT

[dresslered]

As long as I have owned my truck, the heater grids cycle when the outside temperature is precisely 66-degrees and below (with a cold engine) just as the factory manual states. However, for the last several days, we've had temperatures down to 57-degrees and the grid heaters are no longer cycling on! Am I being paranoid or could this mean that my IAT sensor is on its way out?



Additionally, if you guys are noticing such improvements with new IAT sensors (power, fuel mileage, etc. ), why has an "IAT out of tolerance" trip code not been set? At what point would it set? Wouldn't the MAP sensor be just as critical since volume is calculated by both pressure and temperature by the ECM?

 

[David Oxland]

Now you've got me wondering. Mine come on at every start. even when we were in AZ with 100F outdoors.

 

[dresslered]

David-



Are you sure that your heater grids are comeing on at those temperatures, or are you talking about the momentary timed "wait to start".

 

[Bigsaint]

Good question David, inquiring minds want to know.

Your ever faithful diesel student,

Scott W.

 

[Marco]

dresslered,



The IAT reading is used by the ECM to determine if the Grid heather has to be cycled (or not).



What you're telling us, sure sounds like a bad IAT.



The ECM can't determine if an sensor is slightly out of tolerance.

All it can detect is a completly death sensor.



About the MAP sensor, I was wondering the same thing too. I replaced my MAP sometime back. No major benefit. Seems that that thing is able to handle most high boost conditions without problems.



Hope this helps.

Marco

 

[dresslered]

Thanks for the info Marco. It is as I suspected. I have noticed for the last two days (57-degrees as well) that my heater grids do cycle. Earlier in the week, it must have been 57-degrees plus a little bit, which caused them not to cycle. This means that my threshold temperature has shifted from 66-degrees downward. Perhaps, by monitoring the change in threshold temperature, this would be a fairly good indicator that the IAT sensor is on its way out. I have not noticed any degredation in power or mileage, but perhaps the change so far is too subtle.



I also found it interesting in one of your previous posts that the resistance values that you measured were not linear as I would expect (they contained a "knee"). This is not typical of a normal thermistor type sensor. Were your measurements fairly controled?



Thanks again for the info.



David

 

[David Oxland]

About the grids; I'm relying on the volt meter indicating low voltage. ie if I continue to wait I hear a relay open and the voltage rises, all this before cranking. So I believe that the grids are being energized but I better check voltage at the grid.



David

 

[dresslered]

The heater grid operation is also readily observed by watching the head lights go from bright to dim during the heater cycles. The voltmeter, I believe, is getting data from the ECM (like the pressure guage) and thus may not be highly accurate during the initial start-up. The relay toggling that you describe sure sounds like the grids, however. I have wired up LED's to the heater grids so that it is rather obvious when my grids are working or not.

 

[Joe Mc]

Originally posted by dresslered

The heater grid operation is also readily observed by watching the head lights go from bright to dim during the heater cycles. The voltmeter, I believe, is getting data from the ECM (like the pressure guage) and thus may not be highly accurate during the initial start-up. The relay toggling that you describe sure sounds like the grids, however. I have wired up LED's to the heater grids so that it is rather obvious when my grids are working or not.

How'd you wire up LED's, where'd you locate them? Any pictures?

 

[troutlips]

LED grids

I wired LED's from my relays sometime ago and mounted them in my A pillar pod. It is really neat to watch them cycle independantly of each other both before starting and after. Your relays are mounted on the driver side, wheel well (under the hood). As with any relay you have control wiring coming into the relay (coil) and the actual switching contacts. I came off of the switching contacts on the grid side of the relays. That gives me and indication that the relay is throwing and that voltage is going to the grids. It does not tell me if my grids are functional. That is, as stated indicated by the dip in the alternator gauge and lighting.



One side of the LED's go to ground and the other side must go through a droping resistor (1500 ohms) and then to the respective LED. If you do not use the droping resistor the LED's will draw excessive current and burn out immediately. LED's have polarity, so if they do not light up, reverse their direction. It requires 2 wires, one from each relay, being routed up to the pillar. The resistors and LED's are mounted in the pillar or anywhere you prefer. Great gadget... ... these toaster lights. chow

 

[dresslered]

I mounted the LED's in the center console. They are individually wired to each of the heater grids studs located at the intake horn. A picture of the console is at:



https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=19327

 

[troutlips]

Heater grid studs are a great place to mount. The relays are a little difficult to reach. Use ring terminals and solder all connections.

 

[Todd T]

I would hate to have Trout Lips LOL

I have noticed that as the weather has turned a little cold, my bucking is coming back with the Powermax3. all summer it was almost undetectable, but, I had gotten a new lift pump and then installed a pusher. the problem was gone until the last few nights when it got cold 60's>



would that be the IAT acting up, and the Powermax3 just amplifying it?



it makes me wonder.