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Old 04-12-2009, 11:55 AM   #1
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Exhaust popping

When I'm cruising in gear but without applying any accelerator, the exhaust is popping. I'm assuming it's back pressure and it makes me want to open it all up a little bit (or a lot a bit, I'm flexible).

I'm putting a new carb on it so I'll have that side of the engine torn down already and it seems to be a perfect time to put in a new manifold. Should I do it? Also, what should I get?

Rachel

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Old 04-12-2009, 08:43 PM   #2
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When I'm cruising in gear but without applying any accelerator, the exhaust is popping. I'm assuming it's back pressure and it makes me want to open it all up a little bit (or a lot a bit, I'm flexible).

I'm putting a new carb on it so I'll have that side of the engine torn down already and it seems to be a perfect time to put in a new manifold. Should I do it? Also, what should I get?

Rachel
If the popping is happening during deceleration, it's normal & might even sound cool to some folks.

I cant remember if you ever did say you had a 4.2L I6 & what year your jeep is.
These two details would be a big help to me.

The intake manifold on the 4.2L is fine for the MC2100.
when doing the swap, there are a few things on the intake that should remain hooked up.
The intake manifold heater. Needed to keep the air/fuel mix from the carb vaporized, until the manifold warms up. Also it's sender switch.
The CTO switch (or valve) whatever it is, & all the vac lines for it.
The charcoal canister.
The EGR valve.

Now the exhaust manifold (log) can be replaced with a header.
Hedman, & Pacesetter being two companies that make reasonably priced headers for the 4.2L
Both of these companies make a dual outlet header,(6 into 2) in case you are putting duel exhaust on there.

Did I mention, that none of the mods we've been discussing lately, are exactly legal? Nutter, MC2100. Exhaust mods too.
If you don't have Emissions inspections there, you'll probably be OK.

And for the tree-huger in you, it's likely that your engine will run cleaner & more efficiently with those mods, so you won't loose any sleep over it.

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Old 04-12-2009, 08:45 PM   #3
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the exhaust popping may mean it already has some exhaust work done. maybe just a louder muffler, or something. some of the aftermarket exhausts will make popping noise like you're describing.
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Old 04-13-2009, 01:24 AM   #4
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It's an '89 I6.

I have no emissions to worry about, nor are there particularly illegal mods here. You should see some of the stuff on the roads. In theory we get inspected once a year to make sure we have mirrors and reverse lights and all that stuff, but mostly everyone takes their cars to independent <wink> inspectors instead of the BMV.

It doesn't really happen when it's decelerating as much as under load without acceleration. I notice it most going down hills in gear without my foot on the gas. If I press in the clutch it goes away.

Rachel
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Old 04-13-2009, 02:22 AM   #5
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Yeah thats normal mine is doing that than again I have no muffler... it broke off *winky winky* and yeah its kinda like running in a lower gear when your going down a hill, your trans wants to move faster so its trying to turn the engine faster so its kinda like a rumble right or is it more like a backfire?
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Old 04-13-2009, 02:41 AM   #6
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More like a mini-backfire. It's not a no muffler rumble.

R
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Old 04-13-2009, 06:34 AM   #7
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It's an '89 I6.

I have no emissions to worry about, nor are there particularly illegal mods here. You should see some of the stuff on the roads. In theory we get inspected once a year to make sure we have mirrors and reverse lights and all that stuff, but mostly everyone takes their cars to independent <wink> inspectors instead of the BMV.
It does pay to make friends with your inspector!!! An extra $30.00-$40.00 can make them temporarily blind.

Quote:
It doesn't really happen when it's decelerating as much as under load without acceleration. I notice it most going down hills in gear without my foot on the gas. If I press in the clutch it goes away.

Rachel
Yep going downhill in gear with foot off gas, is decelerating.

Any time the drivetrain is pulling the engine.

It's causing a rich condition, & post chamber ignition happens.
In other words some raw fuel gets past the exhaust valve, & ignites in the exhaust system.
Again, some of us like that sound! The deeper the better.
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Old 04-13-2009, 11:59 AM   #8
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Fair enough! I think I'll do the exhaust at some point but that's not a priority right now. Thanks for all your guidance y'all!

R
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Old 04-13-2009, 11:44 PM   #9
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Yep

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