Engine/Transmission (1998.5 - 2002) Does anyone know....

[NoSeeUm]

If you can measure the voltage off of the IAT and compare that to a table to get the actuall IAT?



Thanks;

Jim

 

[Bob Wagner]

just to add to the topic

I would say yes... .



good info here.







Intake Air Temperature Sensor Problem:



I thought I would share with everyone my findings about the low mileage problem, several people have complained about. Seems that no one has ever found a solution for it.

Maybe I have!



During our development I've become aware of the fact that the Cummins ECM calculates the fuel the injection pump has to inject, based on the signal of two main inputs.





Pressure in the manifold AND the Intake Air Temperature.



Obviously the most important input is the pressure measured by the MAP (Manifold Absolute Pressure) sensor. To make it simple, the higher the pressure, then more fuel will be injected. This does not mean that the Intake Air Temperature sensor is less important!

To make it simple again, the higher the air temperature in the intake, the less fuel will be injected.





Hot air is less dense than cold air, thus less fuel has to be injected as the temperature rises.



What happens if the IAT sensor gives a wrong reading of the temperature?



In my case, the IAT sensor wasn't able to read very cold temperatures, but also didn't read high temps. It was like it's temperature range was much shorter than it should have been. When I compared my original sensor to a new one, I also noticed that it's reaction time was way to slow!



Before I proceed, I would like to point out that NO code has ever been set in the ECM/PCM!





The ECM can only detect a completely dead sensor. ( Voltage too high/low )



After finding out that my stock sensor was off of it's values, I proceeded to install the new one.





Installation is very simple. All you need is a 22mm socket and the ability to climb onto the engine since the IAT sensor is located in a very uncomfortable position. It's at the end of the cylinder head towards the firewall, on the driverside.





Here's a link to see where it is located:

http://dodgeram.org/tech/dsl/mt_2_feb98/fuel_sys_comp.htm





Once the new sensor was in, I noticed immediately that the EGT's at idle were about 75°F lower!!! Cruising at 85 the EGT's dropped about 100-120 degrees!!!





Great, and the mileage? Driving like I normally do, MPG is better by 1. 9 miles per gallon!





Yes, that's the number!



Sure, I can't claim that everyone with the "low mileage" has a bad IAT sensor, but I think it's worth it to give it a try. Obviously, I don't know how your mileage will increase, but from what I've seen through the WWW, several people seem to have the same problem like I did!



In my case, since the IAT sensor never gave an high enough reading of the temperature, the ECM was fooled into thinking that the air was cooler than it was in reality. Thus it added more

fuel than could be burned. This little more fuel added wasn't enough to increase performance, but was enough to KILL mileage.



Hope this helps.

Marco.

 

[rweis]

I have noticed that if you watch the overhead mpg as the engine warms up to operating temp that when the IAT? tells the ECM that operating temp is reached the mpg goes up about 5 mpg (I know the overhead mpg reading is not correct, just use it as a release point). At a slow cruise (55) the boost has not changed much, only the engine temp has risen, but it is noticable when the IAT notifies the ECM to notify the VP44 to go to a leaner setting.



I watch the mpg fairly closely as it is a good gauge as to how things are doing as a system. On the same road, at the same speed, same weight, same weather, the mpg in the overhead should be about the same (however incorrect). IF it goes off significantly, something has caused it and the problem solution hunt is on.



Bob Weis

 

[NoSeeUm]

Thanks Bob, that is some good information!



Has Marco ever let you know how he reads IAT?



I would think that Marco reads the IAT either as an internal number in the ECM or as a a direct temperature read out on the back side of the ECM via the diagnostic port.



I know that the Edge Juice has a IAT display. I was wondering if I could do the same or something like it. Either as a voltage / resistance to temperature conversion that I could do manually or as direct temperature read out using a Fluke or some such.



Thanks;

Jim