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Old 03-19-2021, 01:33 AM   #6
kwmech
Senior Member
 
Join Date: Mar 2003
Location: Colfax-California
Posts: 8,720
Re: What are these ?

Early attempt at NOx control. It only allowed ported vacuum to the distributor once the engine was warmed up and the trans was in high gear. Manual transmissions got the AIR pump. Never saw tcs on a manual truck that I remember. This was in California anyways when I had my smog license a few years back. BUT it also varied by the GVW rating of the truck
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