Smog test on 1990 Mazda Miata

I own a 1990 Mazda Miata and it failed its smog test. Does anyone have any
troubleshooting tips?

Thanks!

"liquidoxygen" > wrote in
lkaboutautos.com:

> I own a 1990 Mazda Miata and it failed its smog test. Does anyone
> have any troubleshooting tips?

Can we have some more info? Where are you, different states have
different rules. Why did it fail, be specific please.

If you're tested with an exhaust sniffer take the car out for a run
before the test. Hit the highway and run at least 15 miles at 65mph or
better, then get it tested. That'll get the car warmed up fully and
clean out the combustion chambers and exhaust system.

The early Miata's don't use an EGR valve. So if it failed for NOx make sure
the cooling system is in top condition. High combustion temps lead to NOx
failure. It is also a good idea to run a top engine cleaner through once in
a while to keep the combustion chambers free of carbon. Built up carbon can
raise the effective compression ratio and also lead to higher temps.
Alan
"liquidoxygen" > wrote in message
lkaboutautos.com...
>I own a 1990 Mazda Miata and it failed its smog test. Does anyone have any
> troubleshooting tips?
>
> Thanks!
>

XS11E is correct, you need to give allot more info. I know for one thing, if
your NOX is high you can help quite a bit by retarding the timing.
Especially since so many of us are running around with advance timing.

Chris
92BB&T

"XS11E" > wrote in message
...
> "liquidoxygen" > wrote in
> lkaboutautos.com:
>
>> I own a 1990 Mazda Miata and it failed its smog test. Does anyone
>> have any troubleshooting tips?
>
> Can we have some more info? Where are you, different states have
> different rules. Why did it fail, be specific please.
>
> If you're tested with an exhaust sniffer take the car out for a run
> before the test. Hit the highway and run at least 15 miles at 65mph or
> better, then get it tested. That'll get the car warmed up fully and
> clean out the combustion chambers and exhaust system.
>

"liquidoxygen" > wrote in message
lkaboutautos.com...
>I own a 1990 Mazda Miata and it failed its smog test. Does anyone have any
> troubleshooting tips?
>
Generic catalytic converters, at muffler shops, are cheap
enough. Since there's no EGR valve, that's the only possible
culprit. At least that was the thing I replaced this year to
pass the Texas emissions test with my 1990 Miata. The
numbers changed dramatically, from the first test (fail) to
the second (pass). I'm in a "highly critical" area, suburban
Dallas/Fort Worth, with stricter standards than rural Texas.

Jim Stuyck

It's not that simple even on the miata. If your cat was replaced simply as a
"what else can it be" kind of thing, you simply got lucky that it was the
problem.

Chris
92BB&T

"Jim Stuyck" > wrote in message
. ..
>
> "liquidoxygen" > wrote in message
> lkaboutautos.com...
>>I own a 1990 Mazda Miata and it failed its smog test. Does anyone have any
>> troubleshooting tips?
>>
> Generic catalytic converters, at muffler shops, are cheap
> enough. Since there's no EGR valve, that's the only possible
> culprit. At least that was the thing I replaced this year to
> pass the Texas emissions test with my 1990 Miata. The
> numbers changed dramatically, from the first test (fail) to
> the second (pass). I'm in a "highly critical" area, suburban
> Dallas/Fort Worth, with stricter standards than rural Texas.
>
> Jim Stuyck
>

I have a 1990 Miata too, @ 165,000 miles. Never failed a California smog
test.
Here's what I do to make sure I pass:
(1) tune up - new spark plugs
(2) very recent oil change
(3) new clean air filter
(4) fuel injector cleaning (if needed)
(5) warm car up for at least 20-30 minutes before the test
(6) new catalytic converter if necessary (I've never had to resort to
this)
(7) Get Larry Dennstedt's advice in San Diego (Dennstedt's Auto Repair at
(619)-284-4911)
Dennstedt is a.k.a. "Mr. Goodwrench" with Miatas, also real nice
guy. If anyone can get your Miata to pass smog, he be da man. He wouldn't
charge you for telephone advice. Good luck.


"liquidoxygen" > wrote in message
lkaboutautos.com...
>I own a 1990 Mazda Miata and it failed its smog test. Does anyone have any
> troubleshooting tips?
>
> Thanks!
>
>