To keep it short, I have a question about the use of IM 240 testing on 97 and later Fords running OBDII.
The Ford system used to keep NOX low is done with the EGR system.
This function is controlled by the following, engine rpm, road speed and light throttle application usually in OD or it's possible in third gear under the right conditons.
Does your test procedure force the OBDII system to go into the EGR function?
If not, you may see NOX levels considered to high at a point it's considered legal.
Below this point and at heavey throttle the NOX will be higher with only the cats to offer any clean-up.
Your truck has OBDII that looks at all systems for passing self tests according the PCM program that never changes.
If you have no codes set, the truck is legal per the EPA.
Before you begin replacing parts or doing service on a system with no codes, be sure your not being misled by your testing because the only way you have of seeing any change is by your testing.
Remember, the rest of the world does not have any testing facility and has to rely on OBDII as supported by the EPA as good enough.
Let us know.
Last edited by Bluegrass; 09-15-2011 at 12:37 AM.