"bllsht" > wrote in message
...
> In message . com>,
"Stevil"
> wrote:
>
> >Hello All,
> >
> >My 89 4.2L YJ just failed its smog on HC, results as follows...
> >
> >15mph MAX 124 AVG 34 MEASURE 125
> >25mph MAX 104 AVG 23 MEASURE 104
> >
> >As you can see it was a real close one, it was well below average on CO
> >and NO.
> >
> >I should have put two and two together as I noticed the other day some
> >soot build-up on the tail pipe. SO my question is beyond changing the
> >PCV valve, an oil change, and high octane gas, is there anything else I
> >can do? I changed the PCV valve, distributor cap, rotor and ignition
> >wires three months ago, do you think changing the sparks would help
> >any?
> >
> >Thank you in advance for your time and consideration of this matter and
> >your replies.
> >
> >Cheers, kind regards,
> >Steve
>
> Some soot on the tail pipe is pretty much normal on a vehicle with a cat
> converter. If there was a lot of it, that would indicate it's running
> rich, but if your CO readings were low, it's not rich. High octane gas
> might help a little with high NOx, but won't do a thing for HC.
>
> HC is unburned fuel. Anything that can cause a misfire could cause this.
> Ignition problems, or a lean mixture would be what I'd look for first.
> Make sure the timing is where it belongs. Could also be a dead cat
> or air injection system.
>
Along with the misfire idea, change the spark plugs. If the air injection
system is sub-standard, that would give you a point or two on the HC too.
On a vehicle this old, often the pump seizes up and someone puts plugs in
the holes for the AIR nozzles.

Earle