How to lower the NOx emissions without replacing the catalytic converter?

  • 1998 DODGE RAM
  • V8
  • 2WD
  • 153,000 MILES
I have a 98 Dodge ram 1500 5.2L 318 with 153,000 miles. I have failed emissions testing three times. Did tune-up, replacing plugs, wires, rotor, and distributor cap. Ran fuel system cleaners. The third test showed significant improvement for HC, and CO, both passed. However my truck is failing the NOx test. I took it into a shop to have it diagnosed, the technician said everything checked out good, including the O2 sensors. He told me for $250.00 he would do a chemical treament to clean valves and injectors, and it would take him about four hours to do. He believes this would solve the NOx problem. Also I was told my truck does not have an EGR valve. Any suggestion on how to lower the NOx emissions without replacing the catalytic converter (which was replaced with an after market cat about 12,000 miles ago)?
Do you
have the same problem?
Saturday, November 27th, 2010 AT 1:05 AM

1 Reply


There are a few things that cause higher levels of NOx gasses. For example, higher combustion temps. Is the engine running hotter than it should? Also, there is an EGR valve on this vehicle. Has someone removed it? It should be on the intake manifold.

Take a look at the attached pic below for a description of the EGR system and how it works. Has the EGR or the EGR solenoid been removed? If it has, that is likely what is causing the problem. Make sure to check on the intake manifold, (I believe the driver's side) to see if someone has put a blank plate over the EGR port.

If you look at pic 2, I highlighted the EGR valve so you can locate it. Make sure the vacuum hose to it is attached. If it is, disconnect it from the EGR, and start the engine to confirm there is a vacuum to it. If there is, then I would recommend getting a vacuum pump to confirm it holds vacuum.

Let me know if this helps answer your question or if you have others.

Take care,


See pic below.
Was this
Thursday, August 19th, 2021 AT 10:00 PM

Please login or register to post a reply.

Sponsored links