Muffler Cough

[Alan Lindquist]

On my way to work this morning, my muffler coughed. Or so it seemed. If any of you have feedback, I'm interested.

1980 SC with 225K miles - no known engine work (I bought it with 121K) except for valve adjustments. Motor is in stock configuration.

Engine still has decent compression and runs reliably and within operating ranges for oil burn (1100 miles/quart) and engine temps are just above warm-up range unless it get to be 90+ degrees, then I see mid-gauge temp. It's likely that I'm running a bit rich. I have a cat-bypass J-Tube and Dansk stainless muffler with 84mm tailpipe.

Cool day today - morning in the 50's. Was pulling a long grade at 60+ Mph and about 3,000 RPM and everything seemed normal.

Suddenly it sounded like a subdued backfire, or rather an internal chamber combustion - two in quick succession. It wasn't loud or violent and it didn't seem to come from outside the car like it exited the tailpipe. It sounded more internal.

I looked back to see if maybe I ran over something that sounded like a chamber/exhaust backfire. Nothing in the road. I didn't feel a shudder or impact to the sound and it didn't happen again. Engine continued to run rock solid.

Continued to work, ran through gears up and down, sat at idle at stoplights. Everything seems normal.

What do you think it was?

[Oh Haha]

I suspect it was just the combination of the cool air, the load on the engine, and the CIS adjusting itself.

Mine will cough a bit sometimes but I haven't really paid close enough attention at the time to compare to your cough.

I wouldn't worry about it unless it continues.