Popping in the exhaust - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tex_waco_usmc · 07-10-2013, 11:00 AM

So, Ive been dealing with this situation and wanted opinions before I go and dump money into the truck.

A little about the truck. It is an 87 TBI 350 with 700R4. I am getting a popping noise in the exhaust. I thought it was back firing through the exhaust. So I checked timing and gave it a complete tune-up (plugs, wires, cap, rotor, PCV). Checked timing again. All checked good. Purrs like a kitten minus the popping in the exhaust.

My father and I think that it is a baffle in the muffler come loose and slapping the inside of the muffler. But, I am not convinced. I need to replace the exhaust anyways and have a set of 40 series flows for it. But, before I spend the money to do that, is there a way to check to make sure it isnt a backfire? Suspect maybe a burnt valve or some carbon caked up somewhere allowing fuel into the exhaust.

cory d · 07-10-2013, 11:06 AM

could be lean

tex_waco_usmc · 07-10-2013, 11:12 AM

Quote:

Originally Posted by cory d

could be lean

How would I check that and/or correct it?

82GMCstepside · 07-10-2013, 08:04 PM

Mine does it also. Have new exhaust from engine back. Ive changed cap, rotor, plugs and wires. I checked the vacuum and its good but erratic at times. I have some play in my distributor so I am changing that next. that coulb be your prob.

INSIDIOUS '86 · 07-10-2013, 08:22 PM

This is on deceleration right?
Posted via Mobile Device

Unca · 07-10-2013, 08:44 PM

take a look at the catalytic converter. they are notorious for falling apart and blocking airflow. they can rattle n grumble n block airflow thru the exhaust.

82GMCstepside · 07-10-2013, 09:18 PM

Mine is at idle. No cats on my ride. Its just a slight popping while at idle. Like a small miss. Im restoring her so when I pull the cab off I will change the distributor. That could be it.

lunchbox99 · 07-10-2013, 09:59 PM

need to do a leak down test. could be bad exhaust valve or exhaust valve seat. the pop is probably from explosion in cylinder with exhaust valve not closed all the way or "sealed". could also be carbon build up on piston...I would do compression and leak down test and go from there, cover the basics first.

**Willowrun** · 07-10-2013, 11:38 PM

I agree with Lunchbox. I went through the same thing before....bad exhaust valve sealing. If you recently changed the plugs i'd pull them and look for one that looks different from the rest. If there is one that doesn't look like the others do a compression/leak down to verify poor sealing.
Posted via Mobile Device

82GMCstepside · 07-11-2013, 04:07 AM

Just changed the plugs. Old ones looked all about the same with 3K miles on them. I'll pull em and see after a few miles. Thanks for the info.

tex_waco_usmc · 07-11-2013, 09:13 AM

I found the culpret! I took it to a shop to put it up on a lift and well I found that the baffel in the muffler was so loose and flapping that it beat the inside of the muffler out! LOL Im not joking! I found a crack in the mufflers skin where the metal was protruding outward. The casing looked as if I had bottomed out on the muffler several times all dented and mangled and it has never touched the ground... It was in pitiful shape... Cut it out and the guy had a used muffler laying around. (Ive got flowmaster exhaust for this truck but I dont want to install until she gets closer to the ground.) Cost me $40 and all I did was watch him work! LMAO Doesnt hurt my feelings one bit. Also, no more embarrassing noises coming from this pig.

Rufton · 07-11-2013, 09:41 AM

Quote:

Originally Posted by INSIDIOUS '86

This is on deceleration right?
Posted via Mobile Device

I'd like that. I suppose a healthy cam and unhealthy mpg required.

INSIDIOUS '86 · 07-11-2013, 11:35 AM

Quote:

Originally Posted by Rufton

I'd like that. I suppose a healthy cam and unhealthy mpg required.

Just crack the transfers open a little more and then idle it down with more fuel than it wants then if you straight pipes out the side you can shoot flame. Works great and burns your eyes an makes a lovely smell at idle
Posted via Mobile Device

Rufton · 07-11-2013, 12:43 PM

Sounds like the perfect setup for McDonalds's drive through

07-10-2013, 11:00 AM	#1
tex_waco_usmc Project Heaven in my 67!!! Join Date: Jan 2009 Location: Bosqueville, TX Posts: 899	Popping in the exhaust So, Ive been dealing with this situation and wanted opinions before I go and dump money into the truck. A little about the truck. It is an 87 TBI 350 with 700R4. I am getting a popping noise in the exhaust. I thought it was back firing through the exhaust. So I checked timing and gave it a complete tune-up (plugs, wires, cap, rotor, PCV). Checked timing again. All checked good. Purrs like a kitten minus the popping in the exhaust. My father and I think that it is a baffle in the muffler come loose and slapping the inside of the muffler. But, I am not convinced. I need to replace the exhaust anyways and have a set of 40 series flows for it. But, before I spend the money to do that, is there a way to check to make sure it isnt a backfire? Suspect maybe a burnt valve or some carbon caked up somewhere allowing fuel into the exhaust.

07-10-2013, 11:06 AM	#2
cory d Registered User Join Date: Dec 2011 Location: Arlington WA Posts: 1,728	Re: Popping in the exhaust could be lean __________________ GMC C15 355 SM465 3.73 80 C10 cruiser build thread 79 short stepside crew cab. big and ugly. build thread

07-10-2013, 08:04 PM	#4
82GMCstepside Registered User Join Date: Jun 2013 Location: Raceland, La. Posts: 3	Re: Popping in the exhaust Mine does it also. Have new exhaust from engine back. Ive changed cap, rotor, plugs and wires. I checked the vacuum and its good but erratic at times. I have some play in my distributor so I am changing that next. that coulb be your prob.

07-10-2013, 08:22 PM	#5
INSIDIOUS '86 Registered User Join Date: Jul 2009 Location: washington Posts: 4,178	Re: Popping in the exhaust This is on deceleration right? Posted via Mobile Device __________________ 377 sbc thumpr cam autogear m23 muncie 3:73 Detroit trutrac 3''spintech prostreet mufflers xpipe 1 3/4 headers build thread !http://67-72chevytrucks.com/vboard/s...d.php?t=577217 Iroc gauge threadhttp://67-72chevytrucks.com/vboard/s...d.php?t=554511

07-10-2013, 08:44 PM	#6
Unca Registered User Join Date: Apr 2013 Location: Laporte, IN Posts: 57	Re: Popping in the exhaust take a look at the catalytic converter. they are notorious for falling apart and blocking airflow. they can rattle n grumble n block airflow thru the exhaust.

07-10-2013, 09:18 PM	#7
82GMCstepside Registered User Join Date: Jun 2013 Location: Raceland, La. Posts: 3	Re: Popping in the exhaust Mine is at idle. No cats on my ride. Its just a slight popping while at idle. Like a small miss. Im restoring her so when I pull the cab off I will change the distributor. That could be it.

07-10-2013, 09:59 PM	#8
lunchbox99 Registered User Join Date: Mar 2011 Location: Medford, Oregon Posts: 33	Re: Popping in the exhaust need to do a leak down test. could be bad exhaust valve or exhaust valve seat. the pop is probably from explosion in cylinder with exhaust valve not closed all the way or "sealed". could also be carbon build up on piston...I would do compression and leak down test and go from there, cover the basics first. __________________ 79' GMC stepside...the money pit! 355 aluminum partoit heads 2.02,lunati 268 flat tappet,comp roller rockers 1.6,hi-tech torque link intake(Jim McFarland),electric water pump,650 holley double pumper,msd 6al,msd street fire dizzy,doug's long tube headers(ceramic),3" exhaust(flowmaster 40)

07-10-2013, 11:38 PM	#9
Willowrun Senior Member Join Date: Mar 2013 Location: Ann Arbor, MI Posts: 1,029	Re: Popping in the exhaust I agree with Lunchbox. I went through the same thing before....bad exhaust valve sealing. If you recently changed the plugs i'd pull them and look for one that looks different from the rest. If there is one that doesn't look like the others do a compression/leak down to verify poor sealing. Posted via Mobile Device

07-11-2013, 04:07 AM	#10
82GMCstepside Registered User Join Date: Jun 2013 Location: Raceland, La. Posts: 3	Re: Popping in the exhaust Just changed the plugs. Old ones looked all about the same with 3K miles on them. I'll pull em and see after a few miles. Thanks for the info.

07-11-2013, 09:13 AM	#11
tex_waco_usmc Project Heaven in my 67!!! Join Date: Jan 2009 Location: Bosqueville, TX Posts: 899	Re: Popping in the exhaust I found the culpret! I took it to a shop to put it up on a lift and well I found that the baffel in the muffler was so loose and flapping that it beat the inside of the muffler out! LOL Im not joking! I found a crack in the mufflers skin where the metal was protruding outward. The casing looked as if I had bottomed out on the muffler several times all dented and mangled and it has never touched the ground... It was in pitiful shape... Cut it out and the guy had a used muffler laying around. (Ive got flowmaster exhaust for this truck but I dont want to install until she gets closer to the ground.) Cost me $40 and all I did was watch him work! LMAO Doesnt hurt my feelings one bit. Also, no more embarrassing noises coming from this pig.

07-11-2013, 12:43 PM	#14
Rufton Registered User Join Date: Apr 2013 Location: Knoxville TN Posts: 1,170	Re: Popping in the exhaust Sounds like the perfect setup for McDonalds's drive through

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