Exhaust backfire, blows hole in muffler, now runs much better...what happened?

[a63vette]

Hey guys, I have been having issues with my fuelie running above 3800 rpm for a while, and after replacing plugs, points, checking the fuelie unit e.t.c. I have been pulling my hair out. Tonight I went to start her up, had difficulty and then she hit, ran very rough and bam.....heard a loud backfire and suddenly she started to run like a champ. Ripped a large hole in the right rear muffler but now no running issues..and fortunately as far as I can tell I didn't bend anything internally. Is this common, make sense e.t.c.? The exhaust setup is 20 years old..

Thanks guys,
Jordan

 

[Mac]

Welcome aboard!!

Hi a63vette! Welcome to CAC!

Pretty easy to diagnose this one- your exhaust system needs replacement, sooner rather than later. The hole in the muffler probably saved your engine. You're lucky to have escaped relatively undamaged as it can be dangerous.

The backfire situation you described sounds what happens when the exhaust system becomes plugged. Exhaust fumes contain enough crud and carbon to coat the insides of the mufflers, slowly plugging the baffles inside them.

Eventually, it will restrict the escape of exhaust gases. Most of the time, a partial blockage will reduce your engine's performance enough that you'll notice and start looking to see what's wrong. Another indication would be a hissing sound from the exhaust system caused by the back pressure buildup.

Exhaust gases are not inert- there's enough unburned fuel and oxygen to burn easily. Remember that old trick of installing a spark plug at the exhaust tip to impress your friends with a fiery display of stupidity back in the 60s?

As soon as the exhaust gases leave the combustion chamber, they start to cool. By the time they reach the muffler, there is no fear of the heat causing the fumes to spontaneously combust. If, however, you run the engine at high RPM and your exhaust system is plugged enough, the heat of combustion can ignite the fumes. The result? An explosive backfire and/or an explosive discharge in the weakest point of the exhaust system which is usually the muffler. Does this sound like what you experienced?

The backfire could cause an underhood fire or internal damages as the exploding exhaust gases are forced back into the engine. That'll ruin your day like nothing you've ever seen. It's much better when the muffler takes the damage, rather than the engine.

 

[midyear]

Had a similar situation happen to me: I had bought a 66 BB AC coupe in Yuma AZ, and decided to drive it home to Atlanta (@2200 miles). around Dallas TX it developed a skip and was losing power. plugs, wires, points, carb clean and adjust, no change. I decided to go on with the skip and was hoping since I was just a day or so from home, I thought that I would make it. Stopped for gas, carb flooded, and upon starting, blew both mufflers wide open! car now ran great, and continued to the whole way home. Later replaced mufflers, car still runs great.

 

[a63vette]

Thanks alot Mac/Midayer...thats exactly what happened..scared the hell out of me. Appreciate the welcome, I followed you guys here from the other place.

Jordan

 

[67HEAVEN]

Thanks alot Mac/Midayer...thats exactly what happened..scared the hell out of me. Appreciate the welcome, I followed you guys here from the other place.

Jordan

And we're glad you did!

 

[67HEAVEN]

By the way, Jordan, if you ever hear someone claiming that open headers don't make any difference......now you've got a story for them. :L

 

[a63vette]

67/Mac & others, I gotta say I used to think those guys on the cobra forum (clubcobra) were wacky, but I think with the recent migration, front end parties et al you guys have stepped it up a notch! Glad to be a part of it.

Jordan

(PS, I apologize..I am a Chevy guy, but to be honest those Kirkham bodies turn me on!)

 

[ChuckG]

I gotta laugh, because about 8 years ago, my "super high performance" 54 Corvette started to run badly. To make a long story short, one day I started it, and was greeting with a LOUD backfire and a bang. Blew a hole in the passenger's side muffler as big as my fist. Car ran great after that. It sounded good too. A new aluminized exhaust system solved the problem. So....not just high performance cars experience this....my 8.5/1 compression 6 banger did the same thing. Chuck

 

[Mac]

Back in 1984, I was driving straight truck loaded with fish (ugh!) for a while. It wasn't that great of a job but it paid the bills until something better came along. The truck was an old Chebby and the brakes weren't all that great, so I was accustomed to using the clutch to 'engine brake' myself down the hills.

This particular day, when I downshifted, it started making strange hissing noises. It didn't sound like tires because it was from underneath the cab. I slowed down and was getting ready to pull off the road and the noise went away. I started speeding up again; the noise came back. Being the intrepid youth, I pushed in the clutch and punched the gas a couple of times to see if it would clear. KaaaaaBOOOM! The muffler separated itself from the tailpipe as the motor backfired hard enough to pop open the hood.

After that, the motor started singing with a deep throated roar. I pulled over and checked under the hood which was rather smokey, then headed off to complete my run. It made a remarkable difference in the power available.