guys have an 88 plymouth voyager with the 3 liter v6 in it, and it keeps failing on the NOx what would cause this? they suggested EGR valve we installed a new one and it still failed, help as the emission laws are strict now and i need to use this car

 

usually the egr or timing. check the timing.

 

Also remove the intake and clean the hell out of it. Especially in the area of the egr. If the tunnels running to the egr are filled with crap it can give high readings. I assume you've already done the basics like O2 sensor, plugs, fuel filter, etc, etc.

 

a chart that i have points to several problems that it could be:
1-egr system
2-loose missing vacuum lines
3-ignition timing
4-block or stopped up exhaust
5-fuel mixture to lean
6-carbon builup in the cylinders
7-catalytic converter
I am not a guru this is just off of a chart i use to help figure out why one wont pass the dreaded test----good luck

 

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