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Unread 04-02-2012, 06:06 PM   #1
mcp0526
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1978 CJ5 
 
Join Date: Jun 2011
Location: Stroudsburg, PA
Posts: 89
Popping While Idling. Thoughts?

I have always used my CJ as a DD, but only recently have I started putting 60 miles on it a day back and forth to my new job. The jeep runs great as it always has and it seems to enjoy being used that much.

One thing I have noticed though is an increase in a popping sound coming from my exhaust (headman headers to purple hornies) when at idle. Also, the exhaust smells rich like gas. Could the increased runs and long times at higher RPMs be changing things in there? Possibly cleaning it out? Running around town it doesn't happen as much as after a long commute.

FYI: My commute is ~30 min. highway speeds 75% at 55mph 10% 60mph.

Sounds (and smells) like I might need to lean it out?

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Unread 04-02-2012, 06:16 PM   #2
ahar9
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1994 YJ Wrangler 
 
Join Date: Oct 2011
Location: saint leonard, maryland
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Mine did the same and I have same exhaust setup. I ran some fuel system cleaner through it and it's perfect now
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Unread 04-02-2012, 06:19 PM   #3
mcp0526
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Huh. I just had a bottle of Marvel Mystery Oil in my hand the other day at the store and was weighing whether or not it was worth it.
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Unread 04-02-2012, 06:39 PM   #4
LT1CJ7
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1983 CJ7 
 
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It might have a small intake or exhaust leak.
At idle, It will purr then go pop pop purr pop pop pop ???
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Unread 04-02-2012, 06:44 PM   #5
mcp0526
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Yeah that's pretty much it. Just had the new headers and mufflers installed less then a year ago so I don't think it is an exhaust leak. Excuse my lack of knowledge...what would cause an intake leak?
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Unread 04-02-2012, 06:53 PM   #6
LT1CJ7
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Loose bolts on intake or carb, vacuum hoses, power booster, bad gaskets on intake or carb.
I mainly run into loose intake bolts or bad intake gasket.
I've also had one where the timing was too advanced which seemed to intensify the popping.
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Unread 04-03-2012, 08:19 AM   #7
JeepHammer
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1973 CJ5 
 
Join Date: Aug 2007
Location: South West Indiana
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90% of the time popping out the exhaust is an Ignition issue.

I've done ignition upgrades on several I-6 engines that popped out the exhaust when done with cheap plug wires.
Change wires, adjust timing and the 'Popping' goes way.

The popping you are hearing is unburned fuel getting into the exhaust, then igniting.
if you get two or three in a row, not just one cylinder doing it, then it's usually an ignition issue.

You CAN get too much fuel dumping into the intake, arriving as a liquid (instead of atomized properly) and the heat in the cylinder will cook it into vapor,
When the exhaust valve opens, the fuel vapor is ready to ignite and looks for oxygen.
When it hits oxygen, it flashes over and you get a 'Pop'.

----------------

'Scavenging' is a term used to describe what happens in the cylinder when the intake and exhaust valve are open at the same time, (End of exhaust stroke, beginning of intake stroke there will be an 'Overlap' in the camshaft where both valves are open at once)

The idea is to let the outgoing hot exhaust gasses 'Suck' some of the intake charge through the cylinder,
And that will 'Scavenge' extra exhaust out of the cylinder so the cylinder can COMPLETELY fill with fresh fuel/air mixture.

The amount of scavenging that goes on depends on the back pressure in the exhaust, size of the header tubes/exhaust manifold, and the amount of overlap in the camshaft valve timing.

A free flowing exhaust, large header tubes, large diameter tubes/short exhaust will cause over scavenging,
Sucking the fuel/air mixture out the exhaust port, and when it hits something hot enough to ignite it, it will also make a 'Pop'...

'Shorty' exhausts and large tube headers are really bad about over scavenging...
And when that fuel hits the exhaust and meets something hot, you get a 'Pop'.

Just trying to give you some information that will help and understand why things happen the way they do.
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Unread 04-03-2012, 03:13 PM   #8
mcp0526
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Location: Stroudsburg, PA
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Thanks for the info guys. Funny enough I have everything saved in my Summit Racing shopping cart for the first step of TeamRush or a good tune up (bigger cap, msd wires, and new plugs). I guess I should commit finally huh? I've been waiting for my paycheck! I will put the parts on and see if that helps.
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