# '85 720 not passing emissions test - help!



## briaread (Mar 2, 2012)

Hi there,

My '85 720 with the Z24 engine keeps failing the state emissions test with high CO levels. I've tuned this thing best I can (plugs, timing, all filters, oil change) which got it to pass the HC portion of the test, but the CO level won't go down. Anybody got ideas on what to try next?

Thanks!
Brian Read


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## Snellgelt (Nov 7, 2012)

Can you tell me if you did find a solution?
I'm having the same problem here in Colorado.

thanks!


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## smj999smj (Jan 1, 2006)

Since it's carburated, the thing to do would be to adjust the carburator idle mixture and monitor the reading with a gas analizer, which is something most people don't have access to, unfortunately,


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## Snellgelt (Nov 7, 2012)

Shop has already done that - result were WELL within spec for the NO and HC, but not for the CO (initially 70, now 56 and 40 is the limit) ... in the process we noticed that the prior owner has removed most of the emissions equipment.

Now I am in need of the vacuum switches, AB valve, vapor canister with vacuum switch and check connector, to name a few)

Is there anybody out there ..... who has these parts and doesn't need them? My vehicle is a 1986 (built in 1985) Nissan 720 standard bed, 2wd, Z24 with 5 speed manual.

Doreen
Colorado


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## smj999smj (Jan 1, 2006)

The vapor canister is not going to affect your CO readings; its use is to store fuel tank vapors when the engine is not running until a later time when they can be introduced to the intake manifold and burned in the combustion process. High CO is the result of incomplete combustion and can be caused by a number of things, including a dirty air filter, faulty oxygen sensor (something I would replace if it's original or has been installed for a long time), faulty TPS, faulty ECT or a faulty thermostat.


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## Snellgelt (Nov 7, 2012)

ok - makes sense. I'm looking at my diagram but I don't see "TPS" nor "ECT"- would you please tell me what these are?

thank you so much!


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## smj999smj (Jan 1, 2006)

Well, forget about the TPS as you wouldn't have that. The Engine Coolant Temperature Sensor (also referred to as the "ECT," "Water temp sensor" or "Cylinder Head temp sensor") will "usually" be located not for from the thermostat housing. I don't work on too many Z24S engines these days, so my memory fails. It'll be a two wire plug and the wires will probably be yellow w/ blue stripe and yellow w/ green stripe.


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