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spuggy spuggy is offline
Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 3,523
Originally Posted by torresmd View Post
OK so I just bought my 930 slantnose and went to get it registered here in Arizona and failed emissions. Well to my surprise the car does not have a cat so it failed miserably.
My '78 RoW has never had a cat fitted. It passed the post-registration emissions check in WA after the engine swap (but is exempt from the bi-annual due to age). When I took it to the UK, it passed an inspection there - including the (age-related) emissions portion.

In fact, last dyno guy I used remarked on the gas analyzer output, saying "clean running motor - may be using a lot of fuel, but it's burning it all, nothing wasted".

Without the cat. Just a data point.

Depending on the emissions standards you have to meet, your car may simply be set too rich at idle...

Factory spec gives 2-4% CO2 for a pre-81 930/60, or 2-3 %/1.5-2.5% CO2 for US engine types, depending on year/model.

I find my car runs much better when warming up, or part-throttle driving, at about 3.0 %, but would probably exceed my state's HC limit at anything over 3.25%.

There could be some other issue - like a tough (or non age-related) emissions standard that really needs a cat to pass. Or something that needs to be addressed that's making it not pass.

I'd advise an fuelling/ignition check/tuneup, set the idle CO2 to the low end - say, 1.5% - and drive around carefully off-boost until the motor is good and hot - you may find it'll just sail through the emissions check like that. (Or you may be better off simply connecting the O2 sensor and making sure that that is all working correctly)

Then just richen it up on a gas analyzer until it runs right when warming up and doesn't surge part-throttle under load. Which is where it's running efficiently, and is somewhere around 3.0% on my motor.

If the AZ rolling road test is like the WA one, they'll tell you to shift up if you're making more than 3,000 RPM at the test speed in the gear they originally asked you to be in - so as far as I understand it, idle mixture adjustment is pretty much the only thing in the picture sub-3000 RPM off-boost...

Which would all be a lot less hassle than getting an inspection-only exhaust system, no?

If there's any kind of special flagging that goes on in your state for multiple fails, you maybe want to take it to a shop that knows 930's and has a gas analyzer - for their advice. This free advice may be worth what you paid for it.
'77 S with '78 930 power and a few other things.
Old 01-31-2009, 06:12 PM
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