popping in muffler

[bob911s]

Possible dumb ? When my '77 is cool ( not up to normal op temp )When I shift I get a pop in my exhaust. After I get warmed up it seems to go away. It's a Ca. car and needs to pass state smog. The FI was set up on a smog machine to pass and from taht point on it seems to be a constant problem. " I " think its too rich but taht would stop it from passing. Any ideas?

[Adam]

Could be a bad gasket that seals up when fully up to operating temperature, too. If it allows an air leak, then that could explain your popping sound.

Hold a rag over the (cool) tailpipe while idling and listen for leaks further inside the exhaust. If it's not leaking, it should stall pretty quick.

[RazorRacer]

My guess is the timing. Retard the timing a degree or two and the popping should go away. I don't think it's a problem though.

[v9ff]

I have a 1984 with a Fabspeed premuffler, Borla single out and no O2 sensor and I often get a pop when I release the accellerator upon shifting.

Is the problem really a leak in the exhaust system somewhere? If so, no one has been able to explain to me exactly why this phenomenon occurs. Anyone willing to try?

I know the car is running rich so it can't be a lean issue.

Let me know what y'all think!

[masraum]

The two main reasons for exhaust popping are 1 leaky gaskets (often can make for really loud backfires) and 2 rich condition on overrun. The rich condition on overrun is not necessarily due to anything being set wrong, it's just that when you are coasting there is gas getting into the exhaust, it's often normal. Bob, you are probably getting that when the car is cold because the car runs more richly when cold, so you have some excess gas. Steve, in your case your free flowing louder exhaust is probably why you are hearing the popping. If you hear it when you have only let off of the gas partially then that's fine, but if your foot is not on the gas pedal and you still hear the popping then you may either have an exhaust leak or a leaky injector. You shouldn't have popping if you completely let off of the gas pedal. The DME cuts fuel if you let all af the way off of the gas pedal to increase fuel efficiency.

[v9ff]

Thanks Steve!

That's the best explaination I've heard yet.

[KTL]

Steve (v9ff),

Could be your Fabspeed premuffler does not properly align with the heat exchanger or muffler flange(s). That's the problem I have with mine at the premuffler to muffler flange. Fabspeed had a problem with their jig and the part actually turned out crooked. A number of people had this problem with their product.

[v9ff]

Kevin,

From what I remember of the Fabspeed fitment problem... aren't they like totally off? Around an inch or so? I got lucky with mine and it fit pretty well when I installed it and the joints look very flush. How off is your premuffler?

[KTL]

You're right Steve. Some people's premufflers were crooked by a significant amount. Mine is only off by a slight amount. Maybe 1/4 inch. Still enough to cause a slight leak at the muffler flange.

I doubled the gaskets and loosened the muffler band clamps to allow max. amount of adjustment I could get. Still have a bit of misalignment though.

Mine does fit better than the cat. conv. in one way. With the cat., the muffler seam didn't want to sit in the channel of the muffler bracket (but you could still secure the muffler just fine). Now the muffler seam does fit in the channel with the premuffler on. Just doesn't line up at the flanges too well and causes a mild pop on lift after big throttle opening.

[Superman]

Exhaust leak.