Popping noise out of exhaust

glassbowtie77

glassbowtie77

Well-known member
Joined
Apr 28, 2008
Messages
58
Location
Long Island, New York
I was driving along today steadily at 65 mph, when I let off the gas coming to a red light I noticed a pop pop pop noise coming out of my left sidepipe. Anyone know what causes this?
 
Excessive fuel burning in exhaust due to rich mixture or a lean misfire burning in the exhaust, check exhaust for air leaks too. Since it happens when you let off the gas, it's almost certain a lean mixture and an air leak in the exhaust.
 
Your popping is typically a symptom of a lean condition. When running lean, you get a lean misfire when you let off the gas, and unburned fuel enters the exhaust. Richen up the carb.
 
lars said:
Your popping is typically a symptom of a lean condition. When running lean, you get a lean misfire when you let off the gas, and unburned fuel enters the exhaust. Richen up the carb.
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With a carb, what do you consider lean enough for this to happen...?? 16-1, 17??

:drink:
 
You'll start getting popping in the exhaust in the mid-15 range if you slam the throttle closed and the rear wheels are pulling the engine over.
 
lars said:
You'll start getting popping in the exhaust in the mid-15 range if you slam the throttle closed and the rear wheels are pulling the engine over.
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What does a DPFI unit do under those circumstances...??

I would imagine it would pop it's ass off, but the cats and muffs would kill a RR loco sound, so not know a thing....

:chinese:
 
DPFI does not respond the way a carb does to having the throttles slammed closed - no comparison. The IAC does not immediately seat upon throttle closure to create the sudden closure possible with a carb, giving the DPFI time to enrichen and correct the induced lean condition without popping. California-emission carbs had a dashpot on the throttle lever to prevent the sudden closure, and this would reduce the tendency to get the lean misfire popping: emissions are very high when the lean misfire popping occurs.
 
Nope...the idle table comes back into play...probably high 13's. I have no decel popping even with 3 inch exhaust and very loud mufflers on my EFI 383..
 
lars said:
DPFI does not respond the way a carb does to having the throttles slammed closed - no comparison. The IAC does not immediately seat upon throttle closure to create the sudden closure possible with a carb, giving the DPFI time to enrichen and correct the induced lean condition without popping. California-emission carbs had a dashpot on the throttle lever to prevent the sudden closure, and this would reduce the tendency to get the lean misfire popping: emissions are very high when the lean misfire popping occurs.
Click to expand...

Cute, I remember a car I had that came with TWO idle solenoids....one for the a/c and the other for something else....anyway, it took a bit to get that sorted out and running decent...trying to recall the exact configuration, not to confuse with some friends' car....Distinctly remember two idle solenoids though...:hissyfit::sos:
 
You won't get exhaust popping in the high 13's - that mixture will produce a very smooth and well-sounding deceleration idle. One of the problems we're seeing is that most fuel around the country now has ethanol additives (about 15%), and this causes a lean condition. If you have 15% ethanol, you cannot run mixtures any leaner than about 14.2:1 without getting popping. If I know a carb is going to be used with ethanol additive fuel, I usually set it up in the high 13 range to assure no popping.
 
lars said:
You won't get exhaust popping in the high 13's - that mixture will produce a very smooth and well-sounding deceleration idle. One of the problems we're seeing is that most fuel around the country now has ethanol additives (about 15%), and this causes a lean condition. If you have 15% ethanol, you cannot run mixtures any leaner than about 14.2:1 without getting popping. If I know a carb is going to be used with ethanol additive fuel, I usually set it up in the high 13 range to assure no popping.
Click to expand...

I have heard and from my experiences, for every damn point they stick ethanol in gas, we can just about subtract that from our overall fuel economy....making 15% ethanol content cost us about 12%+ in MPG....

what say YOU???

then I wonder about the hydroscopic aspects of Ethanol, especially here in Florida where ground water can float concrete swimming pools outta the ground, believe it or not.... I dunno if you noticed some older posts of mine concerning this issue and my recurring problems or not...

:eek:
 
lars said:
Your popping is typically a symptom of a lean condition. When running lean, you get a lean misfire when you let off the gas, and unburned fuel enters the exhaust. Richen up the carb.
Click to expand...

might 6 month old gas cause this also?
 
Not real likely, unless the gas tank has been uncapped and exposed to moisture for some time. I have 2 year old gas in one of my cars right now, and it runs flawlessly, and the oil refineries store gasoline in their tanks for periods far exceeding 6 months.

Popping in the exhaust is normally caused by a misfire which allows raw fuel to enter the exhaust system. The misfire is either caused by an ignition system problem (fouled spark plug, for example) or by the mixture being too lean to ignite in the cylinder. A rich mixture, by the way, will seldom misfire. The gas would have to be exceptionally bad to actually be able to cause a misfire from the bad gas alone, and if it were that bad, it would likely cause drivability problems throughout the power range.
Lars
 
Well here's what I found so far. There was an exhaust leak right at the head by cylinder #1, loose header bolts. I went around and checked them all and found several other bolts that needed some tightening as well. I also checked my idle mixture screws as per Lars paper they were 4 turns too rich, should have been 6 turns out, they were 10 out. The idle is much smoother now and the gas smell from the exhaust is way less. Tomorrow, weather permitting, I will test drive it and see how runs. Hopefully my exhaust popping noise will be gone, and my performance and gas mileage will be improved as well.
 
The popping noise is still there. Upon further inspection the header gasket is blown out by cylinder #1 from the bolts coming loose. I am ordering a set of Stage 8 locking header bolts from Summit along with a new set of header gaskets. Any suggestions as to which are the best gaskets to buy? I am looking at a set of soft aluminum gaskets from Percy Performance. They are supposed to seal the best and they claim they are burn out and blow out proof. I am also looking at a set of Mr. Gasket Copperseal gaskets, any opinions on these or is there something else that I should be looking at?
 
I use the same copper gaskets that I bought back in 2005 - Mr Gasket if I remember correctly.... the local AdvancedAuto had them on the shelf but Summit is about half the price, see if they price match Summit's price....
I also have Breslin (that's what the Percy's lock bolts used to be) lock bolts... good stuff as far as I can say... no leaks....:thumbs:
 
glassbowtie77 said:
The popping noise is still there. Upon further inspection the header gasket is blown out by cylinder #1 from the bolts coming loose. I am ordering a set of Stage 8 locking header bolts from Summit along with a new set of header gaskets. Any suggestions as to which are the best gaskets to buy? I am looking at a set of soft aluminum gaskets from Percy Performance. They are supposed to seal the best and they claim they are burn out and blow out proof. I am also looking at a set of Mr. Gasket Copperseal gaskets, any opinions on these or is there something else that I should be looking at?
Click to expand...

I have used the Mr Gasket copper gaskets with good success. You have to retorque them (copper) a few times after they get hot. A thick header flange is also important. The thin ones just don't ever seal well. I look for 3/8" thick.
I also like the Percies header bolts. No tie wire/clip BS.
 
Go with the aluminum gaskets. I have used both al and cu and the al are thicker, softer so they conform to irrigularities better. You have to retorque the al more frequently and more times than the cu, but once they're set they work pisser.

I just bought the ones they sell on the performance isle at Autozone.

Composite exhaust gaskets are just an effort in futility.
 
Slicing the flange, so each tube is individual, usually makes even composite gaskets work.
 
Anybody know what the correct torque setting is for my Hooker sidepipes and how the heck do you get in there to get a socket on the bolts? The stage 8 bolts look like they will take an allen wrench in the center. is there a special tool made to fit in there without damaging the ceramic coating on my headers?
 
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