misfire popping sound through exhaust help with plugs - Chevelle Tech

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post #1 of 56 (permalink) Old Nov 24th, 13, 9:06 PM Thread Starter
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misfire popping sound through exhaust help with plugs

Hey guys my misfire is back again. I'm getting the same constant popping sound through both exhausts at an idle. I pulled the plugs which are a month old and this is what they look like. I think I'm running too lean? The thing is, it smells like gas and just standing behind the car makes your eyes water? What can you guys say about the plugs?

Things i've done:

New wires( one month old msd)

New cap and rotor

Did a valve adjustment and it checked out great.

It's always been misfiring, engine barely has 600 miles on it.

Carb was way too lean when I first got the engine back ( was backfiring through the carb on acceleration, I went up two jet sizes and it went away but car seems like it still doesn't have that power... feels like it wants more gas but I dont know if it's too lean or rich cause it smells like gas and I have that popping sound at the exhaust like it's missing)

am i too lean or rich?
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1970 Chevelle ss clone 454
1968 Dodge Charger R/T 440 six pack
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post #2 of 56 (permalink) Old Nov 24th, 13, 9:18 PM
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Vince
 
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Re: misfire popping sound through exhaust help with plugs

you are getting closer to a good mixture.
what carb-jets-pv-intake???
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post #3 of 56 (permalink) Old Nov 24th, 13, 9:32 PM
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Mark
 
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Re: misfire popping sound through exhaust help with plugs

If you have remote temperature gun , shoot each tube on the headers and see which tube or tubes are running colder , those would be the cylinders to look at . If you don't have a gun, spray water from a bottle on each header see which ones the water don't boil of quickly and look closely at those cylinders . Check the plugs and wires . Check resistance across the plug wires , if you have a meter . Swap the plugs around and see if the problem moves to another cylinder with the plugs , then you'll know it's the plugs .Good luck
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post #4 of 56 (permalink) Old Nov 25th, 13, 12:36 AM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

so am I running rich or lean based on plugs?

1970 Chevelle ss clone 454
1968 Dodge Charger R/T 440 six pack
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post #5 of 56 (permalink) Old Nov 25th, 13, 1:25 AM
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Re: misfire popping sound through exhaust help with plugs

Quote:
Originally Posted by tomwadek View Post
so am I running rich or lean based on plugs?
You can tell by the scent. It will have a really rich scent if it is running rich, and same goes for lean.
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post #6 of 56 (permalink) Old Nov 25th, 13, 1:56 AM
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Re: misfire popping sound through exhaust help with plugs

Check that you are getting spark to all cylinders. Popping through the exhaust could either be raw fuel loading up in your exhaust (more like a boom), or a lean miss. One plug or more will be wet if this is happening.

If you're all good there, I would go up a couple more primary jet sizes and see if it gets any better.
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post #7 of 56 (permalink) Old Nov 25th, 13, 2:16 AM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

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Originally Posted by quan3165 View Post
Check that you are getting spark to all cylinders. Popping through the exhaust could either be raw fuel loading up in your exhaust (more like a boom), or a lean miss. One plug or more will be wet if this is happening.

If you're all good there, I would go up a couple more primary jet sizes and see if it gets any better.
well theres no loud boom just a constant light popping that can only be heard standing at the back of the car. All header tube are 172 degrees and a spark plug tester shows all spark plugs are going off.

If it's too lean why does it smell so rich?

1970 Chevelle ss clone 454
1968 Dodge Charger R/T 440 six pack
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post #8 of 56 (permalink) Old Nov 25th, 13, 8:33 AM
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Tyler
 
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Re: misfire popping sound through exhaust help with plugs

A lean miss will cause an incomplete burn of all hydrocarbons. Might make it smell like raw fuel. Usually this means you are WAY lean.

I don't know anything about your setup though.
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post #9 of 56 (permalink) Old Nov 25th, 13, 1:35 PM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

well I just took it to a carb shop and i had him hear the exhaust and showed him the plugs. He test drove it and said based on everything I'm wayy too lean. The car wants to get up and go but isn't getting enough fuel...

He's charging me 150 to set it up right. hopefully this works...

1970 Chevelle ss clone 454
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post #10 of 56 (permalink) Old Nov 25th, 13, 1:45 PM
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Re: misfire popping sound through exhaust help with plugs

Quote:
Originally Posted by BigBrad View Post
You can tell by the scent. It will have a really rich scent if it is running rich, and same goes for lean.
Woof.

Quote:
Originally Posted by quan3165 View Post
A lean miss will cause an incomplete burn of all hydrocarbons. Might make it smell like raw fuel. Usually this means you are WAY lean.
Yup. If it smells rich, burns your eyes, makes you wish you were breathing farts instead...it's probably lean-misfiring.

Too rich = excess carbon monoxide (CO). CO is colorless and odorless. Doesn't make your eyes water, just kills you quietly.

Too lean = misfire = entire cylinderful of fuel and air goes out the tailpipe--vaporized and noxious.

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post #11 of 56 (permalink) Old Nov 25th, 13, 3:46 PM
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Re: misfire popping sound through exhaust help with plugs

Popping through the exhaust is usually a lean condition which causes an over-heated exhaust.

Most the time, it's a vacuum leak,..which is un-metered air getting to the combustion chamber. With a trained ear, sometimes you can hear the vacuum leak. Otherwise, check each of the vacuum sources, check for the correct carb mount gasket, and check for a leak at the intake manifold.

Also, if your timing doesn't have enough lead, she'll burn warm which will elevate the exhaust temps.

Good luck!
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post #12 of 56 (permalink) Old Nov 25th, 13, 6:28 PM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

ok just got it back. He had to go up a jet size and it's not missing anymore, the rpms aren't jumping and I dont feel it anymore, however; I do still hear the popping in the exhaust at idle but it's sooo faint. I hear it more often in the passenger side exhaust but again it's faint. He said it's because there is still some unburnt fuel sitting in there and it should go away on it's own. Any truth to that? or should I ask him to make it more rich. Car feel responsive now...
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post #13 of 56 (permalink) Old Nov 25th, 13, 6:38 PM
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Re: misfire popping sound through exhaust help with plugs

I hope your carb guy checked for a ruptured power valve, a fairly common problem when it backfires through the carb. You may still have a vacuum leak, check torque on intake bolts and make sure your carb gasket is sealing properly to the intake.

Searching for vacuum leaks can be frustrating, here's my method: Get a can of Gumout choke & carb cleaner and spray any spot you suspect a leak while idling the engine. If idle speed goes up when you spray a spot, you've found your leak.

Your plug gaps look really wide, have you set them to the spec for the ignition system you have?

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post #14 of 56 (permalink) Old Nov 25th, 13, 7:52 PM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

Quote:
Originally Posted by pnugene View Post
I hope your carb guy checked for a ruptured power valve, a fairly common problem when it backfires through the carb. You may still have a vacuum leak, check torque on intake bolts and make sure your carb gasket is sealing properly to the intake.

Searching for vacuum leaks can be frustrating, here's my method: Get a can of Gumout choke & carb cleaner and spray any spot you suspect a leak while idling the engine. If idle speed goes up when you spray a spot, you've found your leak.

Your plug gaps look really wide, have you set them to the spec for the ignition system you have?
It backfired through the carb only once about 8 months ago. I kinda hear a little bit of something coming from the cowl induction hood vacuum. I'll try the carb cleaner tomorrow.
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post #15 of 56 (permalink) Old Nov 26th, 13, 1:10 PM Thread Starter
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Re: misfire popping sound through exhaust help with plugs

heres an update. I did the carb spray thing to check for vacuum leaks and found nothing. I did this at a low idle but the rpm didn't change at all.

The car is no longer burning my eyes if I stand behind it. The right side tail pipe(passenger) has a very very faint popping. The driver side does not anymore.

1970 Chevelle ss clone 454
1968 Dodge Charger R/T 440 six pack
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