Please tell me this isn't as bad as it sounds..

[wgerow]

Turned the key on at the gas station, made a back-fire like noise......now it sounds like there is a hole in the exhaust sys. Heat exchangers are not stock, and they do have a fair bit of surface rust on them, believe my mechanic said the cat was removed....... am fearful it is much worse than exhaust related.

1983 911 SC, 191k on clock. 20+ years of records with no sign of ever been opened up. Always runs like a top, never any problems. Drips a minor amount of oil on the garage when parked. No oil spewing or smoke associated with current event. Drove it home about 10th of a mile.....seemed to drive fine......but I feel sick

listen here:
911 SC - YouTube

[pete3799]

Only way you're going to find out what it is involves jacking it up and getting under it.
Sounds like an exhaust leak to me.

[timmy2]

Lie down beside it with it running and feel for the leak, probably blew out a gasket. (Set your parking brake!)

[Jdub]

What did you see when you inspected the air cleaner/box? Do you have a pop off valve, and did it leave a dent in the filter? If so, it worked. Now, make sure it has set properly and there are no leaks. Test the airbox seal by trying to get a fingernail under any screw - if there is room the box is blown.

Also as per the posters on exhaust. But you always check the airbox after a hard backfire - esp. when the car starts running "differently". Good luck!

[jeffs9146]

Almost sounds like a sparkplug came out!??

[Bob Kontak]

Originally Posted by timmy2

Lie down beside it with it running and feel for the leak, probably blew out a gasket. (Set your parking brake!)

Sounds like right near a head. Too pronounced not to be. Should be an easy find.

[wgerow]

There is a pop off valve
No dent in filter, everything intact, nothing is loose

I have had a spark plug not fully seated before, similar sound but this is ten times louder....and car seems to have full power

I don't have means to lift the car, but crawling under it I tried to look for a hole. Nothing obvious or visually apparent from my limited review, but it does sound like it is very close to the engine, towards front of car.....so maybe yes a hole at/near a header?

Thanks for the help

[budge96]

Sounds like a broken valve spring may allow it to run reasonably decent yet noise rises and
falls with RPM.
Shouldn't be to difficult to isolate determine cylinder afflicted and have a mechanic replace...
Common 3.0 liter problem after 35 odd years on the run...
Bert

[wgerow]

Originally Posted by jeffs9146

Almost sounds like a sparkplug came out!??

Despite my quick dismissal of this suggestion, this was exactly the problem. No 6 cyl. (All the way fwd rhs?). A review of the engine bay in the daylight and I saw the plug wire sitting there, plug still attached. No signs of stress or damage on the plug threads. That plug being the most difficult to access I assume it did not get tightened all the way when replaced last summer. I guess I was too freaked out by the noise to notice the power loss in the short drive from the station to the house.

I installed a new plug and voila, was purring like usual!

Previous plug issue I encountered was a wire not seated on the plug fully....quite a bit different than a plug fully dislodged.

Back on the road

Thanks

[timmy2]

Guess you didn't need to lie down by the car after all...
Glad you found it, and apparently no damage done.

[James Brown]

"this isn't as bad as it sounds"