High NOX

[helpme]

Got a 94 3.0 Ranger and it wouldn't pass emissions. High NOX by almost double.Got 190K miles on it. Last tuneup was done at 140K. New plugs and wires. Cleaned up the PVC valve. Has no EGR. Checked vacuum with guage and its right in the middle of the green. Has a lot of local miles. Not much freeway. Seems to run pretty smooth though. Have run low test gas but have been running hitest lately. Bought vehicle new in '94 and I'm an only driver. Any ideas to get the NOX down? Thanks.

 

[helpme]

More...

I have never seen a check engine light on this truck (except at crankup).
Even if I leave the gas cap off. Is this a shortcoming of OBD-I?

 

[BeaterMan]

you said it doesn't have a egr? did it have one at one point and someone omitted it or did it never have one? that could cause high NOx and so could ignition timing.

 

[graff104]

you said it doesn't have a egr? did it have one at one point and someone omitted it or did it never have one? that could cause high NOx and so could ignition timing.

says he is the bought it new in 94. Try pulling the codes just cause the light isn't on doesn't mean there is not something stored that might point us in the right direction.

 

[helpme]

I'll do that. Here are the numbers. On the 25/25 test it read 2407. Max GA. legal is 1121. On the 50/15 test it read 2432. Max GA. legal is 1227. So they're real high not just a little bit.

 

[macarchie]

Was this issue resolved? I have the same problem with a '91 (no EGR and high NOX). Curious to know what the answer is.

 

[BRUTUS_T_HOG]

turn the ignition timing down when you go to get it tested..

and you are SURE you have no vacuum leaks