Hi: Bought a 93 Rodeo a couple months back(3.2L with 200,000 miles), overall very happy with it but a couple things are bothering me.
It had a high Nox reading on the E test and in order to pass I had a tune up(plugs, wires, timing,oil change), replaced the EGR and catalytic. After this work I failed again and the way I squeaked through was to have the shop do the test with the engine cold. This was at the advice of a Isuzu mechanic and the ppm went from 900 to 400. Any thoughts on why or what else may be wrong?
The other issues are when warm the engine idles up and down from around 700-900 rpm. The last observation is I have never had a vehicle that would start this well in sub zero weather(-35 C) but needs to be coaxed into going whem warm. Not getting a CEL.
Have a feeling all these things are connected but don't want to have my mechanic changing parts until the right one is found.
Apprecite any help

O2 sensors maybe?

Also, have you changed fuel filter, cleaned fuel injectors, and checked the fuel pump?

Haven't a clue, honestly, just guessing. Good luck

Since most of the emissions stuff is bypassed until the engine warms up, I'd start there.

Re-check the EGR valve, and ensure there is vacuum at the hose that goes into it (just pull it off when the vehicle is running and put your thumb on it).

Also, test your PCV valve by taking it off the vehicle and shaking it. You should clearly hear the ball bearing shake inside of the case.

Strange that it's not throwing a CEL.

Steve

Since most of the emissions stuff is bypassed until the engine warms up, I'd start there.

Re-check the EGR valve, and ensure there is vacuum at the hose that goes into it (just pull it off when the vehicle is running and put your thumb on it).

Also, test your PCV valve by taking it off the vehicle and shaking it. You should clearly hear the ball bearing shake inside of the case.

Strange that it's not throwing a CEL.

Steve

Thanks for the replies, will get at it when the snow stops and it warms up above freezing.

Steve brings up some good points. Check your EGR system over. This is the system that reduces/controls nitrous oxide levels by *cooling* the combustion temps a bit. This is likely why your mechanic suggested getting the smog test done while cold. A cold engine will have lower NOx, but higher hydrocarbons due to the catalytic converters not being up to temp. Cats wont do much for NOx, so you may have not needed to replace that in the first place. A clean (cool) combustion chamber, proper spark plugs, proper ignition timing, funtioning EGR, and maybe a tip-top cooling system are pretty much the only ways to control NOx.
G/luck
Joel

Thanks for the replies, will get at it when the snow stops and it warms up above freezing.

Heh, no problem.

OT, I've got a set of coveralls from the Ontario Ministry of Transportation that keep me warm even in -35 C weather :)

They are the ones that the truck inspectors wear on the side of the highway. I aquired them from someone who had them assigned to them and never returned when they retired.

I just put my thermal body suit on, and that on top, and man do I stay warm. The only bad thing is is when the gloves come off, your hands freeze quickly.

Mind you, it does kind of suck sometimes working *under* the vehicle with 8" of frozen snow and ice though.

Good luck!

Steve