| Re: Emission Controls [message #325038 is a reply to message #325016] |
Tue, 17 October 2017 09:03   |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma:
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Learn each system and what they do. There was no A.I.R. or exhaust heat riser on a GMC and it predated. EGR and Cats started fully in 75 but was exempt due to GVW
Non Calif emissions had:
1)Evaporative emissions- a great thing with self regenerating charcoal to catch vapors and reburn. Could only imcrease mileage by minimiziing evap and
Reburning
2) Early fuel evaporation or called AC AutoThermAC carb air preheat. This blended hot and cold air to keep intake air at about 115F. This helped during warmup cycle and minimized fuel pooling and cyl washdown. It kept the air to the Qjet at a more consistent temp so the engineers could tune slightly leaner without drivability issues as fuel vaporized more easily. Under heavy throttle the blend door motor has low vacuum signal so the spring returns it to full cold air so no performance downside. In warm weather it is wide open anyway due to high underhood temps.
3) TVS Thermal Vacuum Switch. Allows ported vac signal to distributor 99% of time. If coolant gets over 220F the switch snaps and sends manifold vac to the dist. This picks up idle speed if in a traffic jam etc and aides cooling. My GMC runs cool at idle in extreme temps simply because there is no road load heat to disipate. This only actvated once or twice when a traffic jam happened immediately after high speed cruise and road load heat did not have time to shed. A great device in this situation. It worked great, then after a few minutes the switch snapped back to ported and idled dropped slightly.
Calif vehicles had a second charcoal canister as well as a complicated throttle kicker setup to control idle speed. They also had specifc Calif carbs and distributors. Someone else will have to chime in on these as mine is Federal and never laid eyes on one.
I see only good reasons to keep 1,2,and 3 above as good running and low emissions usually run hand in hand. If you are misfiring during warmup you are poluting air and your oil. If you are overheating your NOX emmisions may go high.
John Lebetski
Woodstock, IL
77 Eleganza II
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