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.
