Hi everyone. Yesterday, during a normal drive on a flat road surface at about 40 MPH, the muffler on my 71 Cutlass "exploded". Looking under the car, I can clearly see where the buttom of the muffler has torn away near where the bottom and sides meet. Prior to this event, I could smell gasoline when I stopped the car and parked it. I think I had unburned fuel accumulate in the muffler until: "KABOOM!". Now, I need to figure out were to start in the troubleshooting process. I've read a few threads on on this web site related to this problem but I'm not sure where to start. Points, Plugs, Timing, Ignition Condenser, Carb, Choke? Can anyone offer some advice? Car has the original 350 in it if this helps.

Thanks!

 

I'd start looking at timing. Retarded timing will pop through the exhaust.

 

Are you sure the muffler didn't just rust out? I had one recently that looked like a bomb had gone off ... but it was just rusted out.

 

Look down into the carb with the engine running and make sure it's not dripping fuel also when the engine is off.

 

Thanks for the info rec'd so far. I'm fairly certain it wasn't a rusted out muffler. It was just installed 6 mos ago.

 

“Prior to this event, I could smell gasoline”
If you smelled Gas before the Big-Bang, then start checking all of your fuel lines, carb, Charcoal canister, etc for leakages.

Question:
Have you converted your rubber fuel hoses to Ethanol rated fuel lines?
Have you replaced your accelerator pump in the carb with a new Ethanol rated pump?
While cruising at 40 mph, did your car bog down and start to stall before the explosion?
Or did is just go Kaboom?

Theories:
If your car died while cruising at 40 mph for a few seconds due to an intermittent ignition failure and then the ignition reactivated, that would cause the problem you have described.

My other theory is its time for a carburetor rebuild, along with new points, plugs, Disturber cap and cables.

Common muffler explosion scenarios:
#1 Turn off the ignition while traveling at speeds over 30 mph. Coast for several seconds then turn on the ignition.
Gas will accumulate in the exhaust system and when you turn on the key, Kaboom. The longer the key is off the bigger the boom.
#2 Cold engine flooding due to carburetor issues and or dirty/damaged plugs.
This problem happened to my 71 CS. I had a damaged (squashed electron) on one of my plugs.
On cold mornings, I had to be careful to keep from flooding and backfiring until the engine was Hot.
I eventually found the damaged plug and have not backfired in a year.
The damaged plug would not fire reliably when cold.
While searching for the cause, I Rebuilt the carb, Replace the distributor cap, Points, Plug wires, adjusted timing, and corrected vacuum issues. I still had the backfiring issue until I removed and discovered the bad plug.

 

sound like it's running rich and pooling in the muffler till kaboom!

 

I had a 72 Chevy truck with a 3 on the tree and a stove bolt 6. Wind that baby up in 1 rst or second and kill the key for 10 seconds and then hit the ignition. Thing would backfire so loud it sounded like a sonic boom. I used to go through a lot of mufflers.

 

We did that back in the day!

 

I've seen bad condensers do that,but driving along at 40 mph you should have felt the engine cut out prior to the boom.

 

A bad condenser is not intermittent, it will run like kaka all the time if that was the case.

 

Its that Tonawanda water!

 

I was going to guess turbo rocket fluid

 

Bent prudunsal rod leading to a muffler bearing failure.

 

It could have been a muffler bearing failure but we have not eliminated the possibility that the kanootering valve stuck!. This is common when the finagling pin works loose.

 

i had a nissan truck do the same thing. it ended up being the timing. it sounded like a cannon

 

You are wrong I've seen probably 50 times in a 7 year period that a condenser caused this kind of back fire. I used to work in a parts store back in the 70's and it wasn't a surprise when we say one. I've seen you argue against this several times and who knows why it happens but it does. I just know that people that replaced a muffler and didn't replace the points and condenser would be back within a month with a brand new muffler blown to hell.
Sorry to buck you but I just speak from hands on experience, you see a lot of odd unexplainable things working in a parts store.

 

In most of the cases that I've witnessed in about 40 years of working on cars it's a fuel issue, too much unburnt fuel. But hey, I'm not too old to learn something new. A condenser is a cheap replacement.

 

Old thread, but figured I would share my experience.
I had a 71 Chevy pickup with a wooden floor in the box. When my muffler "exploded" and blew a hole in the box, it was due to the plug wires being installed incorrectly. So my cylinders were firing out of sequence and consequently caused a lot of unburnt fuel to accumulate in the muffler.

Lesson learned: never let anyone work on your vehicle that you don't trust and even if you trust them, verify.

d1

 

Just a quick update - I started with replacing the plugs and wires. To date, I haven't had any new "explosions". The car does sit in a heated garage during the winter months here in New York - so, I only put about 40 miles on the car with new plugs and wires before putting it away. I'll keep everyone posted. My project for the upcoming year will be to convert the front drum brakes to disc. If anyone has any experience with a conversion like this, I'd love to hear about it. Thanks.

 

I had one explode like a bomb while I was in the car. I was a poor college student and my idle stop solenoid was malfunctioning so the car dieseled after turning off the ignition. To stop the dieseling I used to give it gas and it would stall out almost immediately, except one time.... the engine revved very quickly and suddenly BOOM!!! The unburned fuel accumulated in the muffler and the resulting explosion scared the s**t out of me. And the is how I learned what and idle stop solenoid was and what it is for.https://classicoldsmobile.com/forums...es/redface.gif

 

Another way to handle dieseling is to turn off the car when it is in drive.

 

Yup, live and learn. Not sure if my gut spilling actually helped anyone, hopefully it did.
Still not sure if my muffler bearing had anything to do with it at all.

 

Or dump the clutch.