Engine/Transmission (1998.5 - 2002) IAT sensor (cleaned )

[Pit Bull]

Just a heads up, the service manual states that you should throw away the old O ring and install a new O ring when you take out the IAT sensor.

 

[jlccc]

IAT and exhaust brake

Several people have postulated that exhaust brakes increase the "fouling" rate of the IAT. I disagree for the simple reason that when the exhaust brake is in use, no fueling is taking place.



In my opinion, what CAN cause increased fouling is high turbine drive pressures. You guys who like to run 30+ psi of boost with the stock HX-35 and 12cm housings with blocked wastegates have turbine drive pressures in excess of 60 psi. During the period of valve overlap that 60+ psi of drive pressure overcomes the 30+ psi of boost pressure and forces combustion products through the cylinder and into the intake plenum. I believe this is a more likely explanation of how the IAT fouling happens. On a stock turbine housing--wastegated at 20 psi--drive pressure is much lower and combustion products are not forced back through the cylinder and into the intake.



Doesn't this sound a bit more likely than use of an exhaust brake?

 

[thepitts]

I replaced mine

I did not clean mine I just replaced it with a new one. I was told that this was not a well cared for part when installed from the factory. The sensors come in a big box, pull one and install. Well after replacing mine and then driving about 250 mile trip my mileage which had not been above 15. 6 before, now this tank was 18. 1 so yes I am pleased. As always your mileage may vary

 

[Cummins Cowboy]

Just reading through this thread, and noticed some compalints about the dealer and not getting a good price for the IAT sensor. you have to remember if you are just Joe blow off the street the parts dept is going to charge you like 30% more than if you are a garage or mechanic. Whenever i buy any part for that matter anymore i always just say that I am from Garrett auto. Just use your last name and put auto on the end so they think you are a garage. LOL works everytime

 

[Diesel Freak]

Re: IAT and exhaust brake

Originally posted by jlccc

Several people have postulated that exhaust brakes increase the "fouling" rate of the IAT. I disagree for the simple reason that when the exhaust brake is in use, no fueling is taking place.

Not always true. Some people leave the exhaust brake on while the truck is idling... to warm the engine up faster. Exhaust gas reversion takes place on valve overlap, and the intake manifold does indeed soot up.

 

[Diesel Freak]

just picked up an IATS from the dealer... . $28. 05



going to see whay 55-60 F reads, and get a resister for that value... . time to play around a bit.

 

[Diesel Freak]

Just did the following experiment on the new AITC I purchased today.



Using two Fluke Multimeters: one connected to the AITS, and the other hooked to an exposed junction K type TC I checked the resistance values from 71. 7F down to 66. 5F. Ambient air temperature was 71. 7F. I lowered the temperature by throttling 80-PSI N2 at varying rates through a 1/8” nozzle.



The TC was in physical contact with the AITS thermister.



Resistance values are accurate within +- . 1F, and resistance values are accurate within +- 20 OHMS



Temperature readings and resistance values were allowed to stabilize for 30 seconds prior to taking readings.



Resistance Values are in kOHMs

T (F) R (kOHMs)

71. 7 = 11. 65

71. 4 = 11. 77

71. 1 = 11. 89

70. 7 = 12. 01

70. 3 = 12. 16

70. 0 = 12. 28

68. 8 = 12. 78

67. 0 = 13. 76

66. 5 = 14. 15



Next I am going to plot the values on a graph. They should produce a straight line.

 

[Vaughn MacKenzie]

Cliff, got a suggestion: instead of adding a resistor in place of the IATS, why not add one in series with it? Say about 10K? That way it will think it is cooler than it is but still be somewhat relative to ambient temperate. I know over there it wouldn't be any big deal but try driving in my area in July when it's 110 and it's fueling like it's 50 out. Can we say lots of smoke and poor mileage?



Vaughn

 

[Diesel Freak]

Originally posted by Vaughn MacKenzie

I know over there it wouldn't be any big deal but try driving in my area in July when it's 110 and it's fueling like it's 50 out. Can we say lots of smoke and poor mileage?



Vaughn

hehe, yeah. . gotta help fight the West Nile Virus somehow

 

[Diesel Freak]

My graph is not quite linear, but it is close enough (used graph paper)



73F should be around 11000 ohm

60F should be around 17500 ohm



however it would not be a good idea to run a 17. 5k resistor when it is 110F outside... you may kill all the Mosquitos in the state.



Who in Arizona wants to give this a try?

 

[dresslered]

Good data Diesel Freak:

 

[Diesel Freak]

Nice plot David... .



I wish I was able to collect accurate data from 32-100F, but I could not get readings to stabilize.



it looks like we could fit an exponential decay function to the graph if we had more data.

 

[dresslered]

I must say that I have watched the discussions on the IAT sensor for quite some time and yet was never convinced enough that it was worth checking. Well finally, after turning 40k miles on my truck, and ALWAYS getting about 15mpg running empty, I decided to check this out for myself.



I am running a completely stock ETH engine. I have had a Jacob's exhaust brake since 4,000 miles and use it daily. Ninety-five percent of the time I run the truck completely empty while the rest of the time I carry a 4000+ lb. slide-in camper.



When I removed the IAT sensor, I noticed that it was very oily (as others had suggested) but everything was mechanically intact. I saw no reason to believe that this amount of contamination would cause any sort of "insulating" or "slow-reading" effect that so many people have suggested (I’m fairly convinced that a slow acting sensor will not degrade the performance noticeably as it would eventually equalize to the ambient). What I did find was that the sensor resistance read 9. 75-kohms at 69 degrees Fahrenheit. This seemed a little low from the other values posted, but didn’t really give me any great concern. I had wanted to test the sensor across large temperature band but since we were expecting company shortly I decided to just clean the sensor and reinstall it. After cleaning the sensor with a little carburetor cleaner, the sensor was easily transformed back to its original white and clean condition. After drying, I measured the resistance once again. I now measured 11. 58-kohms at the same at 69 degrees Fahrenheit! What this suggests to me is that this oily buildup is actually slightly conductive allowing a parallel path for current thus lowering the overall resistance of sensor.



I realize that this mechanism has been discussed before but I never really gave it much thought until I actually saw it for myself. I am still not sure as to how much effect this will offer to the performance of the engine, but I am dying to see my next fuel mileage calculation. Initial performance did not seem to change any. If this is truly a problem (mainly for us exhaust brake users) it seems that the fix would be to apply some kind of insulating coating to the thermistor leads which would prevent the bridging effect, or relocate the sensor as Marco has done. Stay tuned…. .

 

[Alan Reagan]

Perfomance change won't be noticeable. Fuel consumption decrease should be noticeable.

 

[WTBurke]

IAT cleaning & specs

From March 2002 a good read with excellent photos.

www.dodgeram.org/tech/dsl/sensors/IAT/clean.htm



William

 

[dresslered]

It is a good article but I didn't put a whole lot of faith into the resistance vs. temperature numbers. They should be a little more linear than they show.

 

[WTBurke]

David, yes I see this however, in electronics +/- 15% is normal then of course in resistors there is "silver band" @ 5% and "gold band" @ 2% +/- and mil-spec @ 1% (if my memory serves me correctly) If we could find the manufacture of these thermistors (the spec grade) we could make our own for about $2 bux and spec them out mil-grade for the device. Securing them so they don't get sucked into the combustion chamber is a major requirement.



As Marco said earlier... blow-back from an exhaust break on valve over lap is most likley stressing the resistive qualities of these devices and of course the substraight changes thus giving an error in resistive total at a given temperature. I tend to agree with the overlap theroy due to the "hot" temperatures that the device is exposed to in even a short time period.



Thermistors are not considered "dead on" temperature sensing devices however, there may be closer tolerance devices available that would "track-truer" than what we have as an OE device.



William

 

[dresslered]

I'm not overly conserned with the absolute tolerance of the device, but rather a linear curve would be more in line with what one would expect from a thermistor. I would imagine that the data was obtained from various sensors and measured under different conditions thus giving the "general" guideline. It would be interesting to run a "controlled" test using several samples to get a true characteristic guideline.



I'm not sure that I am buying into the stressing of the substrate theory, as if you read in my previous post, I noticed that the lower resistance values were restored just by cleaning the device. I am really starting to believe that this is a result of a conductive contaminent (carbon?) that is providing a parallel path. Again, my observations should be taken lightly as I am basing this theory on my single sample. It does seem to be in line with what some of the others are claiming as well (i. e. cleaning the sensor and reinstalling).





P. S. I realize that Alan tried to get me to check my IAT sensor back in June conserning my lower than normal fuel mileage! :{

 

[WTBurke]

Good point David,

Parrallel resistance due to conductive film such as carbon would really mess up the soup. I've got 34k on this truck and mine was not carbon fouled at all but the base resistance at 70'F was near the limit of tolerance according to the spec chart for this thermistor. I've not changed it out yet but I'll look into it soon.

Fouling this and allowing a parrallel path to develope is unexceptable but, something at say... 10k that is changed to 8k due to a carbon conductive path thats a darn good change!

I'm curious... on cleaning how much of a change in static resistance has some of the guys observed?



William

 

[dresslered]

William-

I would think that you would be alright where you don't have an exhaust brake. Mine looked just like the ones in the pictures (Yech! An oily mess!).



If I could get a proper sample of about 5 bad ones vs. 5 good ones, it might be worth while to do a temperature check. Not only would we get to compare absolute resistances, but we could see how quickly they track to the ambient.