69 472 BACKFIRING THROUGH EXHAUST [Archive] - Maximum Torque Specialists Cadillac Forums

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TONY793

11-03-2005, 07:16 PM

HEY GUYS,
I AM NEW TO THIS FORUM AND AM LOOKING FOR SOME ANSWERS TO A PROBLEM WITH MY 69 DEVILLE. IT IS ALL STOCK AND I JUST HAD THE CARBURETOR REBUILT AT A SUPPOSEDLY REPUTABLE LOCAL SHOP. THE CAR STARTS RUNS AND IDLES FINE, BUT WHEN I DROVE IT HOME AND MASHED THE THROTTLE ON THE HIGHWAY CRUISING TO ABOUT 85MPH THE ENGINE BACKFIRED THROUGH THE EXHAUST WHEN I RELEASED THE ACCELERATOR BLOWING UP A NEW MUFFLER. I FIGURED IT MIGHT BE RUNNING TOO RICH SO I BROUGHT IT BACK AND HAD IT ADJUSTED MORE LEAN BUT STILL HAD THE SAME PROBLEM. ANY SUGGESTIONS?

cadillac chap

11-03-2005, 08:34 PM

are you talkin bout it back firen after you let up suddenly after haven it mashed? or just lettin off the gas while driven? cause if you let up after haven it mashed you gonna drop fire with the sudden rpm an fuel changes. which will cause some fuel to be sent threw an then theres your backfire. if your machine is all dialed in correctly, carb and timin then just dont lift up suddenly. altho you prolly dont have your timin an carb adjusted to mesh togather very well. im sure someone will have some tips better than this. an how to eliminate it. you can use o2 sensors but i have lil knoweledge on it.

DOC

11-04-2005, 10:18 AM

If the engine backfires on deceleration only, it is generally caused by a leak in the exhaust in front of the muffler.

DOC

Nashalac

11-04-2005, 10:37 AM

Or if the engine has an AIR system and it running rich it will explode again in the exhaust when the added oxygen is pumped in.

shwing

11-04-2005, 05:19 PM

Had the same problem with my old truck. I tightened up the nuts at the ends of the exhaust manifolds where the Y-pipe attaches and problem solved. Just be careful, the studs and nuts are usually pretty rusty and you can snap them off. A good spray with penetrating oil (WD-40) and let them soak a while before you start wrenching.

TONY793

11-05-2005, 06:48 AM

THANKS GUYS,
IT SEEMS THAT SHWING WAS RIGHT. I TIGHTENED THE DONUT AT THE Y PIPES AND THAT SEEMS TO HAVE BEEN THE PROBLEM. THIS FORUM IS GREAT AND I'M SURE I'LL BE BACK WITH MORE QUESTIONS REGARDING THESE TORQUE MONSTERS.