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Courtesy of Mike Wassall
Passing
Smog (Hopefully)
|
EXHAUST GASES |
||||
ENGINE
CONDITION |
HC |
CO |
CO2 |
O2 |
NOX |
Retarded
timing |
Decrease |
Same
or increase |
No
change |
No
change |
Large
decrease |
Very
retarded timing |
Some
increase |
No
change |
Some
to large decrease |
No
change |
Large
decrease |
Advanced
timing |
Increase |
Same
or less |
No
change |
No
change |
Large
increase |
Rich
mixture |
Some
to large increase |
Large
increase |
Some
increase |
Decrease |
Decrease |
Lean
mixture |
Increase |
Large
decrease |
Decrease |
Increase |
Some
to large increase |
Very
lean mixture |
Large
increase |
Large
decrease |
Decrease |
Large
increase |
Some
to large decrease |
Ignition
Miss |
Large
increase |
Some
decrease |
Some
decrease |
Some
to large increase |
Some
to large decrease |
Compression
loss |
Some
to large increase |
Decrease |
Decrease |
Increase |
Some
to large decrease |
Worn
engine |
Increase |
Increase |
Decrease |
Decrease |
Same
or less |
Air
injection |
Large
decrease |
Large
decrease |
Some
to large decrease |
Large
increase |
No
change |
EGR
working |
No
change |
No
change |
Some
decrease |
No
change |
Large
decrease |
EGR
leaking |
Increase |
No
change |
Same
or less |
No
change |
Same
or less |
Cat
working |
Decrease |
Decrease |
Increase |
Increase |
Decrease
with 3-way cat |
With the coming of Smog II, aka treadmill
smog testing to my area soon, Ive been doing some reading
up on smog testing/controls etc. As luck would have it, a
friend who is in the trade and studying up for his end of Smog
II, meaning his testing license, was kind enough to lend me some
of his books. So the table above is a compilation from the
prep books for the state test. I am not a smog tech, or
automotive professional, it is just a hobby. While the
above chart should hopefully prove useful, I do have a few more
comments to pass on from my readings and personal experience.
If your car has an O2 sensor it has
to be working to have a chance of passing. Test it with a
decent quality analog meter or any digital multimeter. With
the engine running and warmed up, the O2 sensor should be putting
out about a half a volt, DC. Actually the books say
averaging .45 volts. And it should be bouncing back and
forth, always swinging up and down, from .15 up to .7, at least,
more likely from less than .1 up to over .8. But it should
be up and down. And the testing should be done with it
hooked up to the harness, not disconnected. If it is zero,
it is likely dead, they do die and replacement is recommended
every 30k, test it disconnected from the harness to verify, and
replace it if necessary. I have had them last much longer
than that and not much over 20k, so you never know. A high
reading indicates rich, low a lean condition. If it runs
low, it will probably pass as long as it isnt misfiring, as
long as you dont have to pass Nox. If it is rich, it
probably wont pass. At idle, adjusting the bypass
screw in the AFM can compensate for some excessive richness, but
really isnt the cure but may work as long as you can get it
to cycle up and down. A tight exhaust system at least to
the cat is necessary, it turns out an exhaust leak is something
of an in and out thing and will suck in some air and give a false
reading to the O2 sensor which will in turn richen things up
since it sees too much oxygen.
If your car is pre oxygen sensor,
adjusting the AFM bypass screw will make a definite change in
your idle readings, back it out to lean it out, but will make
little if any difference in high rpm emissions.
High CO indicates a rich condition
according to the state books. But it can also be caused by
gas in the oil if it has been running too rich, so change the oil
if CO is high or you suspect it might be. It tends to be
more of a problem with carbureted cars, but sticky or dirty
injectors could also do it on injected cars.
My friend the smog tech says often, not
always, but often using the Guaranteed to Pass
stuff from the auto parts store will in fact make it pass. I
have never used it, but he says it frequently works. Fuel
injector cleaner can also help, I have had some success with
Techron, and I have heard very good reports about something
called I think it is BK44. I havent used it, I dont
even know who makes it, but those are the only two that seem to
get recommended.
If you are fighting a high Nox problem,
or even if you have to pass it, the state test books say running
premium gas can help. Id always thought premium was
just for octane, but apparently it can do a little more in some
circumstances.
A warmed up cat can make a huge
difference, I recently smogged my 87 E24 project car that has
all of 180 miles on it in the past two and a half years. At
first on the machine it was reading about 600 PPM on HC, which is
way too high. After a good high RPM burn in (70F degree day
and the car was already warmed up to normal temp with an 80C
thermostat) the idle reading dropped to 44PPM, and the 2500
reading was 6PPM. Now I have a problem, I know that, I need
to put some miles on it and figure out what is going on, but that
shows what a good working cat can do. But it shouldnt
be necessary, a 528i with a bad cat, but running good is likely
to be about 200PPM. Borderline for passing, but nothing
like my 6er was.
Passing smog, the number one thing is
make sure the timing isnt too far advanced, that will
make it very hard to pass. Even try retarding the timing a
bit as long as they dont check it like they are supposed to
in California. But it shouldnt really be necessary on
528is and the 530i already had very retarded timing. And
make sure the vacuum retard is working also or else that will
create related problems. Make sure it is running right and
in good tune, plugs OK or better, fresh points if it has them,
reasonably clean oil and air filter. One thing that might
make a little bit of difference if youre are right on the
borderline is adjust the valves a little loose, that is the same
as a milder cam and could make the difference if you are close,
loose like .014, or .016, or even .018, but it will make noise at
that point but shouldnt hurt anything besides your ears.
Like I said, Im no expert on this
subject, but I do know (or have read) a little bit. I hope
this will help you pass what is always a very anxious time for
me, smogging a car.
Mike Wassall
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