Knock Sound - The 1947 - Present Chevrolet & GMC Truck Message Board Network

85Silverado · 12-08-2002, 09:01 PM

I'm hoping this isn't a Knock from the lower part of the engine. It's a bit deeper sounding then a lifter tap but not as deep as a few other knocks i've heard. But that could just be this one hasn't progressed that far. Would a dead cylinder make a knocking sound? I was getting a bit of backfiring and would smell lots of fuel from the exhaust and it wasn't running as smooth as usual. So I started pulling plug wires while she was running and after numerous shocks i finally came across a plug wire that didn't change the idle any when unplugged. It's not the wire cause it would spark to the frame....and my finger....so I'm thinking it's a dead plug. Would that make a knocking sound? Or is my engine dying? Thanks for any info.

P.S. Also checked around A.I.R. fittings and exhaust manifolds for leaks and have none

Paul D.
'85 Silverado

85Silverado · 12-09-2002, 07:22 AM

No one know's anything?

79BIG10 · 12-09-2002, 08:00 AM

Best bet would be to replace the plug and make sure that the wires aren't arcing against each other. To check this pop your hood while it's at night and running. You should see the arcs if any then. Shine your flashlight where the arcs are to know where to seperate wires while truck is not running. Other than that hopefully not a bearing about to go or worse a rod.

85Silverado · 12-09-2002, 10:13 AM

Well, I've narrowed it down to a dead spark plug. Switched the plug with another in the engine and same noise same idle quality and if i pulled the wire on that plug it was the same as when it was in the other cylinder. So I'm hoping the noise is a dead cylinder and not a bearing or rod.

I kinda got my hopes up about the dead cylinder tho...the dead spark plug is on the same side as the noise. Well, keeping my hopes up, still got another hour before parts stores open. Wish me luck.

85Silverado · 12-09-2002, 07:33 PM

Well, I changed the plug, and still the same sound. I think I might have an exhaust leak somewhere in the Ex. Manifold near the flange. I started her up after installing the plug and some puffs of blue smoke came from down by the flange. I'm begining to think (and hope) that maybe the heat riser is stuck closed or that the flange is coming apart. Too cold to get on the ground to look closer, but tomorrow will be considerably warmer so I hope to check those possibilities out. If it's not those...my engine is dying *sobs* lol

Bowed · 12-09-2002, 08:55 PM

Quote " Would a dead cylinder make a knocking sound? I was getting a bit of backfiring and would smell lots of fuel from the exhaust and it wasn't running as smooth as usual . "

Take a compression check.

12-08-2002, 09:01 PM	#1
85Silverado Registered User Join Date: Dec 2002 Location: Milwaukee, Wisconsin Posts: 198	Knock Sound I'm hoping this isn't a Knock from the lower part of the engine. It's a bit deeper sounding then a lifter tap but not as deep as a few other knocks i've heard. But that could just be this one hasn't progressed that far. Would a dead cylinder make a knocking sound? I was getting a bit of backfiring and would smell lots of fuel from the exhaust and it wasn't running as smooth as usual. So I started pulling plug wires while she was running and after numerous shocks i finally came across a plug wire that didn't change the idle any when unplugged. It's not the wire cause it would spark to the frame....and my finger....so I'm thinking it's a dead plug. Would that make a knocking sound? Or is my engine dying? Thanks for any info. P.S. Also checked around A.I.R. fittings and exhaust manifolds for leaks and have none Paul D. '85 Silverado

12-09-2002, 07:22 AM	#2
85Silverado Registered User Join Date: Dec 2002 Location: Milwaukee, Wisconsin Posts: 198	No one know's anything? __________________ Paul D. '78 C20 Scottsdale 350ci 3 speed with granny gear 14 bolt rearend My trucks are "Car-Guy safe".......which pretty much means death trap in the hands of a normal civilian.

12-09-2002, 08:00 AM	#3
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,774	Best bet would be to replace the plug and make sure that the wires aren't arcing against each other. To check this pop your hood while it's at night and running. You should see the arcs if any then. Shine your flashlight where the arcs are to know where to seperate wires while truck is not running. Other than that hopefully not a bearing about to go or worse a rod. __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

12-09-2002, 10:13 AM	#4
85Silverado Registered User Join Date: Dec 2002 Location: Milwaukee, Wisconsin Posts: 198	Well, I've narrowed it down to a dead spark plug. Switched the plug with another in the engine and same noise same idle quality and if i pulled the wire on that plug it was the same as when it was in the other cylinder. So I'm hoping the noise is a dead cylinder and not a bearing or rod. I kinda got my hopes up about the dead cylinder tho...the dead spark plug is on the same side as the noise. Well, keeping my hopes up, still got another hour before parts stores open. Wish me luck. __________________ Paul D. '78 C20 Scottsdale 350ci 3 speed with granny gear 14 bolt rearend My trucks are "Car-Guy safe".......which pretty much means death trap in the hands of a normal civilian.

12-09-2002, 07:33 PM	#5
85Silverado Registered User Join Date: Dec 2002 Location: Milwaukee, Wisconsin Posts: 198	Well, I changed the plug, and still the same sound. I think I might have an exhaust leak somewhere in the Ex. Manifold near the flange. I started her up after installing the plug and some puffs of blue smoke came from down by the flange. I'm begining to think (and hope) that maybe the heat riser is stuck closed or that the flange is coming apart. Too cold to get on the ground to look closer, but tomorrow will be considerably warmer so I hope to check those possibilities out. If it's not those...my engine is dying sobs lol __________________ Paul D. '78 C20 Scottsdale 350ci 3 speed with granny gear 14 bolt rearend My trucks are "Car-Guy safe".......which pretty much means death trap in the hands of a normal civilian.

12-09-2002, 08:55 PM	#6
Bowed Registered User Join Date: Oct 2002 Location: where it's hot Posts: 1,059	Quote " Would a dead cylinder make a knocking sound? I was getting a bit of backfiring and would smell lots of fuel from the exhaust and it wasn't running as smooth as usual . " Take a compression check.



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