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450 SEL deceleration backfire

Started by 90077merc, 27 June 2021, 01:15 AM

90077merc

Hello,

My 450 SEL is backfiring on deceleration. Also I have no catalytic converters. I heard this is usually an air flow sensor or engine timing issue. Any thoughts?
1974 450 SEL

daantjie

Do you have any other anti -smog crap fitted?
Daniel
1977 450 SEL 6.9 - Astralsilber

UTn_boy

^^ What Daniel said/asked. 

If you have a U.S. car it would have been fitted with emissions and smog equipment.  Lack of catalytic converters won't cause backfiring.  If your secondary air injection is still hooked up and working, then you probably have a bad diverter valve, vacuum leak, a bad switchover valve, and maybe a combination of those things along with other issues.  Otherwise the ignition retard/advance is or is not working.  Backfiring is only caused by incorrect fuel mixtures and incorrect ignition timing.....sometimes both.  However, the air plate housing shouldn't have anything to do with the back firing. 

Do us all a favor and please tell is the year that your car was manufactured (on tag inside of drivers door jamb if a U.S. car), as well as if it is or is not a U.S. model.  Once we know that we can further help you.  The 450sel pretty much spanned the whole of the 70's, with each year having different things for different markets. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

90077merc

1974 450 SEL. It's manufactured for California  :o. I would need to check the engine again to see if the smog equipment is still there.
1974 450 SEL

UTn_boy

Here is a schematic of California emissions for 1974 V-8 cars.  Follow this schematic to make sure that everything is in its place or properly blanked/plugged off. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo