720World

Little Trucks, Big World

Hi guys,

Well, it's again time to get the shaft in Cali, especially Los Angeles.

My truck runs very well, but it IS borderline on the HC and NOX. Smog from 2 years ago passed by a hair, but it was so close I'm not holding my breath on it passing this time.

So I have done the following already...

Rebuild the carb, new O2 sensor and the computer IS cycling properly in closed loop.
New thermostat, new vacuum hoses, distributer is rebuilt and all new ignition components for a proper tune up. EGR and PVC valves are ok and working properly.

What I really need is someone with a gas analyzer to properly tune the truck. The star stations around here will only test, and of course no one want's to help you actually tune up your vehicle.
They'd rather have it fail so you can get into the Cali run around.

Does anyone know anyone that can look at the truck with an analyzer to actually tune it properly without running a full smog first? I may need a new cat as well, but can't know that without the proper tests. My goal has always been to keep the truck running stock and correctly, but it seems that no matter how carefully I keep it maintained, it is getting slowly worse.

Any help would be great, as no one really knows how to work on the z24 without making things WORSE.

Thanks.

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Marc: When you say "studied up on the inter-relationship of the various gases and the color of the plugs," can you share what you learned (or, at least, where you learned it)?

My truck's been begging for a tune-up for the longest time, and I've finally got some time this weekend.  Going to set the valve lash, but I'm also thinking about taking another look at the plugs and seeing if there's any other tuning I should be doing.

Essentially..... Google.  

Lots of reading up on smog, emission gases, tuning, a bunch of youtube videos, etc.

I just read till my eyes bled and put it together.  I used to think that my plugs were fine, being a grayish color and very clean.  But according to some mechanics out there, the ideal should be a light brown when you hit near perfect combustion.

Then I looked at my last smog and the numbers.  In a perfect combustion you should end up with ZERO or close to it oxygen at the tail pipe.  I had 4.5%  So I was running lean.  This caused a possible lean misfire driving up HC and NOX, even though CO was very low.  I suspect that it was also too lean to properly light the cat, so I riched out the mix until

O2 was at 0.3% and after a delay (I guess the cat lit up) you could see the HC and NOX drop.  A LOT.

I have of course learned that NOX is also a byproduct of high combustion temperatures, so a properly working EGR valve and Cooling system to keep the head cool is very important.  I run the stock 180degree thermostat.  You MUST pay attention to this, as many parts places will give you a generic 190 or 195 degree thermostat.  NOT good for the Z24.

Anyway, it goes on, and it's a bunch of reading.  But I learned a lot more from it.  Also realized that the feedback system in these truck NEEDS a lot of leeway to operate properly, so unlike other cars, tuning lean is BAD.  You have to let the feedback do it's work.

My truck always ran good, by any measure, but now it runs quite noticeably stronger.  I'm honestly surprised at the difference that made.

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