GMC Sonoma Failing CA Smog

My 99 Sonoma - 2.2L, 5-speed - just tanked on new CA smog test. Failed
the NO measurement at 25 mph, which I understand is new, more stringent
test. Max is 527, I measured 876. Passed NO at idle. HC measure 0.0
(pass), CO measured 0.01 (pass).
Anybody got an idea of what I am looking at with this high NO
measurement? Truck feels like its running fine. No "Check Engine"
light ever. New AC platinum plugs a few months ago.
This vehicle doesn't even HAVE an EGR valve, which would be my first
suspect.
I am told that a lot of vehicles are failing on this test.

Thanks

On Fri, 25 Feb 2005 wrote:

> My 99 Sonoma - 2.2L, 5-speed - just tanked on new CA smog test. Failed
> the NO measurement at 25 mph, which I understand is new, more stringent
> test. Max is 527, I measured 876. Passed NO at idle. HC measure 0.0
> (pass), CO measured 0.01 (pass). Anybody got an idea of what I am
> looking at with this high NO measurement? Truck feels like its running
> fine. No "Check Engine" light ever. New AC platinum plugs a few months
> ago. This vehicle doesn't even HAVE an EGR valve, which would be my
> first suspect. I am told that a lot of vehicles are failing on this
> test.

Could be nothing more complicated than excessive carbon buildup in
combustion chambers. Give it an Italian Tuneup (can of BG 44K or bottle of
Chevron Techron *concentrate* in 1/2 tank of gas, drive around until
you're down to almost empty, take it out on the highway and go up some
hills at high speed in 2nd or 3rd gear. Get those revs up there. This will
frequently blow a great deal of crap out of the combustion chamber and may
well drop your NOx levels substantially.

No timing to set, and as you say, no EGR valve, so if this doesn't do the
job, the reduction portion of your catalytic converter is the next
suspect.

In article
.com>,
wrote:

> My 99 Sonoma - 2.2L, 5-speed - just tanked on new CA smog test. Failed
> the NO measurement at 25 mph, which I understand is new, more stringent
> test. Max is 527, I measured 876. Passed NO at idle. HC measure 0.0
> (pass), CO measured 0.01 (pass).
> Anybody got an idea of what I am looking at with this high NO
> measurement? Truck feels like its running fine. No "Check Engine"
> light ever. New AC platinum plugs a few months ago.
> This vehicle doesn't even HAVE an EGR valve, which would be my first
> suspect.
> I am told that a lot of vehicles are failing on this test.
>
> Thanks

Given the low HC and CO numbers, I suspect that it's running lean.
This can be verified by observing the fuel trim readings on a
scan tool.

> wrote in message
oups.com...
> My 99 Sonoma - 2.2L, 5-speed - just tanked on new CA smog test. Failed
> the NO measurement at 25 mph, which I understand is new, more stringent
> test. Max is 527, I measured 876. Passed NO at idle. HC measure 0.0

> (pass), CO measured 0.01 (pass).

Engine is running HOT -- lean >> perhaps bad gas!




> Anybody got an idea of what I am looking at with this high NO
> measurement? Truck feels like its running fine. No "Check Engine"

Last time you had a (tune-up) service done on that engine, how many miles ago?

Also was it done by a repair facility -- what items were R/R?

I'd scope the ignition system >Spark Plug Gap<

How many miles, what's the odometer read?


BBA

Here's what GM just told me: I took it to big GM dealer early yesterday
a.m.. Sat and waited for emissions guy to get in. He took one look at
previous test results and said, "Oh, you're running 89 octane, aren't
you? (yes, I was) "Run it out, run a full tank of Chevron 93 through
it, bring it back to me when its almost empty. I will test it while you
wait and I guarantee it will pass."
He never even looked at the truck or tested it. He told me, "I don't
have to look at it. There's nothing wrong with that truck." He
explained that -- since '99 and later 2.2 do NOT have an EGR system --
many are doomed to fail new, stricter CA NOx standards at slow speed IF
you take the test on regular (89 octane) gas.

Well, so at least the EGR controversy is settled. It'll take a while
to run a full tank of 93 octane through it. Then I'll take the test
again.

You need to cool down the combustion chamber temp.. run Redline's Water
Wetter through the radiator, that'll usually help out.
Also run a high octane gas, and you should pass just fine.

> wrote in message
oups.com...
> My 99 Sonoma - 2.2L, 5-speed - just tanked on new CA smog test. Failed
> the NO measurement at 25 mph, which I understand is new, more stringent
> test. Max is 527, I measured 876. Passed NO at idle. HC measure 0.0
> (pass), CO measured 0.01 (pass).
> Anybody got an idea of what I am looking at with this high NO
> measurement? Truck feels like its running fine. No "Check Engine"
> light ever. New AC platinum plugs a few months ago.
> This vehicle doesn't even HAVE an EGR valve, which would be my first
> suspect.
> I am told that a lot of vehicles are failing on this test.
>
> Thanks
>

Final chapter on this story: Ran out the regular gas and ran thru two
tanks of 91 octane Chevron per GM advice. Also took it up and down
hills on freeway in 2nd gear at high RPM night before test. Took it
back for re-test yesterday with fingers crossed. Passed w/flying
colors! NOx reduced from around 900 down to 78. There were no codes in
the computer indicating anything else amiss so all I spent was the
extra money for premium gas. Beats the heck out of an $800 cat!
Now...back to regular gas.