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post #1 of (permalink) Old 07-09-2001, 01:36 PM Thread Starter
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Exhaust Issues???...

Well I have what I think is an exhaust issue but it may not be...When I idle or downshift when driving I get a popping sound like a real mild backfire. However it only occurs when I am off the gas...I did fix a pretty big leak at the connection of the exhaust manifold and the pipe itself which made it a little better...

As far as I can tell it isn't an engine issue...The engine seems to idle fine and doesn't seem to be skipping at all...But for further info that may help I have adjusted the timing and the idle mixture a little bit but both of those seemed to help the problem and not hurt it...

Well now that I have said so much I will shut up...Tell me what you think...I have only theories since I am only a "Rookie with a Wrench"...

Josh Lavalleur
'70 CJ5 4.3L V6
D27 & D44 axles
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post #2 of (permalink) Old 07-09-2001, 01:41 PM
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Re: Exhaust Issues???...

Timing could be off a little, or it could be running rich. doesn't sound like an exhaust problem to me.

78cj5 4.2

post #3 of (permalink) Old 07-09-2001, 02:44 PM
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Re: Exhaust Issues???...

Probably not the exhaust. Sounds like your timing is a little retarded (not mentally retarded...the opposite of advanced). When you are on the gas, the vacuum advance advances the timing. When you let off the gas, the engine vacuum drops, thus "turning off" the vacuum advance and alters your timing. I guess that the timing could be too far advanced also. Get yourself a timing light, they are pretty cheap, and set you timing with the engine at idle. Im not sure how much advance your engine will need..probably 4-6 degrees of advance. This means the plug is firing before the piston is at TDC (top dead center or the top its stroke). Of course, if that 4.3L is a later model, computer controlled engine, none of this applies...except that the timing should be set for about 2 degrees of advance. Hope this helps...good luck.

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post #4 of (permalink) Old 07-09-2001, 02:53 PM
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Re: Exhaust Issues???...

I'd check the exhaust again. Maybe try plugging it and listen for pressure escaping ahead of the muffler.

post #5 of (permalink) Old 07-09-2001, 05:58 PM
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Re: Exhaust Issues???...

I'd vote for the air leak in the exhaust probably near or at the manifold.

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post #6 of (permalink) Old 07-09-2001, 09:56 PM
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Re: Exhaust Issues???...

This is a similar issue with my buddies bronco. He is running 2" dual exhaust with glasspacks. He first had a 302 in it. It did just like you said . It'd pop when you let off the gas or engine braking. After a bit he swapped in a 351 but kept the same exhaust. The popping stopped. Maybe the exhaust was too "open" for the 302 which caused it to pop, but adequate for the 351 which eliminated the popping. Thats the only conclusion I can ,make.

post #7 of (permalink) Old 07-09-2001, 11:04 PM
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Re: Exhaust Issues???...

I will bet on the exhaust leak my daughters cavalier does the same thing .I haven't been able to get that thing to seal since I changed the muffler .sometimes I get it just about sealed and it rattles loose again..
How dide you fix the leak if it is one of those patch kits forgetaboutit they dont work.

Learn to let go of what does not serve you ,but forces you to serve it
why does everyone ask if I am gonna paint it ?
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post #8 of (permalink) Old 07-10-2001, 07:08 AM
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Re: Exhaust Issues???...

Mine did the same thing about two years ago. It was a leak right where the pipe attaches to the manifold. The popping went away when I fixed the leak. Like previously posted, check the exhaust from the muffler forward.

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