ORIGINAL: Ken

Oxides of Nitrogen (NoX) are usually created by overly high cylinder temperatures during combustion. Generally speaking, EGR problems are a major cause of high levels of NoX. One of the problems that occurs on Magnum engines is the clogging of the EGR port passage inside the intake manifold. What happens is: When the engine controller allows exhaust gasses to re-enter the intake (exhaust gas recirculation), it reduces the amount of fuel through the injectors. This is because EGR gas is inert; it doesnt help the burn in any way. If inert gas takes up, say, 10% of the volume in a cylinder, you'd need to reduce fuel by 10% to keep the proper mixture. If the inert gas doesnt get there, the fuel mixture is too lean; the major cause of high combustion temp.

I really think you need to get to a shop or dealer that can accurately monitor the PCM. The Chrysler DRB3 can actuate the EGR system, which should make the truck stall if done at Idle. If it doesn't stall, either the valve isn't opening, or the passage is gummed up.

Here in MA, we also have the IM240-style emissions testing. There is a list of qualified service centers that are state-approved to make emissions repairs. If you spend a certain amount at one of these shops, and your car still doesnt pass, you get a waiver. If you go to a shop not on the state's list, you get no waiver no matter how much you spend. Choose your shop wisely, and read the info they gave you with the rejection sticker. There's usually some good info there.