Piston Slap: An Emissions Digression, Dodging Diverted Air?

Sajeev Mehta
by Sajeev Mehta
piston slap an emissions digression dodging diverted air
TTAC Commentator Nate writes:I’m working on a 1979 Dodge D200 with 360CID V8 4BBL carbureted engine, automatic trans, A.I.R. pump, EGR valve, and charcoal canister for the fuel tank hydrocarbons. The underhood factory decal says “California Medium Duty Emissions” and it has no catalytic converter from new. So here’s my situation:
  • All hoses, pipes etc. are there and all valves etc. are working .
  • The A.I.R. pump works but the diverter valve has failed (vacuum diaphragm leaks) and is in the open position so it’s always blowing fresh air into the exhaust manifolds.
Is it likely to pass the emissions test like this? I took my Ca. smog tester license training in 1984 and honestly only remember bits and pieces. So far I’ve not been able to find a new or good used diverter valve. Please advise!Sajeev answers:I know you’re a handy guy, so let’s assume the other items are sorted: horn/all lights work, good brakes, legal tires, carb is tuned up, fresh spark plugs/wires/filters, etc.You should sail past the emissions test because — as you suggested — a medium duty, 3/4 Ton truck in 1979 (or even 1/2 tons back in 1978?) rolled out of the factory lacking a catalyst. I can’t find where such a vehicle fits in California’s rules, plus if it was ever sold/registered in California in the past, odds are its emissions testing bar is set low! Check out the “evaporative” section here, there’s a chance you just need a functioning charcoal canister with intact rubber hoses!I reckon it’ll be just as they say about any pre-1975 vehicle: nothing!As a bonus, considering the air injection reactor pump (smog pump) is stuck in “lower emissions” mode (i.e. always thinning out the exhaust with fresh air) you should pass with flying colors. Granted, those colors are dirty shades of brown with shameful amounts of that killer clear stuff, but an emissions-exempt antique is a historical relic and not a menace to urban living.Good luck finding another diverter valve! After working on a buddy’s 1991 Ram 150, finding several body and (Central) Fuel Injection components were shockingly impossible to procure from the usual places. Certainly not impossible with a few calls to the right junkyards, but your high malaise-era emissions equipment? That’s a totally different kind of pain: I recommend making its part number a saved search in eBay. [Image: Chrysler Corp.]Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.
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  • R Henry R Henry on Mar 06, 2019

    If all smog control devices are present, AND emissions are within spec, you will pass. The pass threshold for 1979 medium duty trucks is VERY low. The inspector is VERY unlikely to notice that failed component. Does your truck backfire ALOT on decel, as my old Nova did with that failed valve?

  • -Nate -Nate on Mar 06, 2019

    You are correct however, I can't find anyone who'll touch the Holly 4165 carby, it's leaking a little bit out of the rear bowl, my brother did some OnLine research and Holly says this leak is common and normally caused by incorrect, too high float level . California's AQMD is very vigilant about hassling smog test stations looking for reasons to yank their licenses, once I find someone who'll take the carb apart, repair it , re install and adjust so it passes the tail pipe test, I can take it to a test onlty station and it'll fly through . My brother who's no mechanic, decided to make a problem out of this instead of letting e handle it so it's all moot for the moment . -Nate

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