Weird knock under load

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

chevyfs

Full Access Member
Joined
Jan 21, 2022
Posts
55
Reaction score
17
Location
michigan
First Name
ray
Truck Year
1986
Truck Model
Chevy C10 Rwd P/U
Engine Size
4.3liter V6
I can't tell what's going on in the video, but a knocking or rattling under load is often just detonation, AKA spark knock or ignition knock.

If it's actually rod knock or something else major, it will usually make the noise while reving just in park or neutral too.
Thats what i was thinking as well. Would the the timing vaccum not being hooked up cause a spark knock?
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,281
Reaction score
6,278
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Thats what i was thinking as well. Would the the timing vaccum not being hooked up cause a spark knock?
That would be a great way to have an incorrect timing but too r-tarded, so it would be driveabilty mess. not sure how likely to make a nosie but im guessing some
 

80BrownK10

Full Access Member
Joined
Oct 22, 2019
Posts
1,878
Reaction score
1,240
Location
Greenwood, SC
First Name
Nate
Truck Year
1980
Truck Model
K10
Engine Size
350
I can't tell what's going on in the video, but a knocking or rattling under load is often just detonation, AKA spark knock or ignition knock.

If it's actually rod knock or something else major, it will usually make the noise while reving just in park or neutral too.
My first thought was spark knock too just by his description. I have not watched the videos though. My work F150 is a 2020 with the 5.0 and that is the most spark knockingest thing I have ever driven. Underload when low in the rpm range it will go to town.
 

80BrownK10

Full Access Member
Joined
Oct 22, 2019
Posts
1,878
Reaction score
1,240
Location
Greenwood, SC
First Name
Nate
Truck Year
1980
Truck Model
K10
Engine Size
350
xc_hide_links_from_guests_guests_error_hide_media
In the video you can hear the engine in idle, then in gear under load spinning tires, then me starting the truck after it stalled, then it also goes into an extremely low idle after warmed up. Now that its low on gas it sounds worse or the knock is just getting worse
That for SURE IS NOT SPARK KNOCK!! Something in that engine is about to let go. Possibly leading to a window mod to the block. I would pull that motor and or swap it with another one.
 

Dave M

Banned
Joined
Jul 30, 2019
Posts
602
Reaction score
1,305
Location
Australia
First Name
Dave
Truck Year
1976
Truck Model
C10
Engine Size
454
I reckon first up I would drop the torque convertor cover and have a visual inspection there. Process of elimination.
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,281
Reaction score
6,278
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
I would also say dont discount a ground out of a non critical comonent that isnt obvious or seemingly likely source.
 

bucket

Super Moderator
Staff member
Super Moderator
Joined
Aug 3, 2010
Posts
29,298
Reaction score
24,601
Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
That for SURE IS NOT SPARK KNOCK!! Something in that engine is about to let go. Possibly leading to a window mod to the block. I would pull that motor and or swap it with another one.

I agree, that last video tells a lot. That's an 'all the time' noise and not a noise just under load.

The engine seems to have a pretty good miss in it too. So it is possible that the shake is causing something loose (like torque convertor bolts) to make one heck of a racket. But it's also very likely that something internal is about to let go and that is the reason for the miss.

That last video really sounds like an engine that is about to go kablooey.
 

chevyfs

Full Access Member
Joined
Jan 21, 2022
Posts
55
Reaction score
17
Location
michigan
First Name
ray
Truck Year
1986
Truck Model
Chevy C10 Rwd P/U
Engine Size
4.3liter V6
I agree, that last video tells a lot. That's an 'all the time' noise and not a noise just under load.

The engine seems to have a pretty good miss in it too. So it is possible that the shake is causing something loose (like torque convertor bolts) to make one heck of a racket. But it's also very likely that something internal is about to let go and that is the reason for the miss.

That last video really sounds like an engine that is about to go kablooey.
It makes zero noise in park thats just whats ******* with me
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,281
Reaction score
6,278
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
It makes zero noise in park thats just whats ******* with me
neutral too? If not in neutral it would be your transmission then when the park lever or internal mechanisms for park are engaged differently. is your shifter adjusted
 

chevyfs

Full Access Member
Joined
Jan 21, 2022
Posts
55
Reaction score
17
Location
michigan
First Name
ray
Truck Year
1986
Truck Model
Chevy C10 Rwd P/U
Engine Size
4.3liter V6
neutral too? If not in neutral it would be your transmission then when the park lever or internal mechanisms for park are engaged differently. is your shifter adjusted
it doesn't make the noise in neutral either, and my shifter is a little finicky, when i try to go into reverse i have to wiggle the shifter around a little in order to get into reverse sometimes. and one time i went to shift and the indicator didn't move at all but the shifter moved, then it slapped into place.
 

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
3,773
Reaction score
6,853
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
LS Swap! Don't forget the cats, nobody likes a stinky engine. Or, it could be a cracked flexplate. I had that happen and it sounds exactly like you're describing. Since you'll have to pull the trans, you might as well have that LS standing by.
 

chevyfs

Full Access Member
Joined
Jan 21, 2022
Posts
55
Reaction score
17
Location
michigan
First Name
ray
Truck Year
1986
Truck Model
Chevy C10 Rwd P/U
Engine Size
4.3liter V6
LS Swap! Don't forget the cats, nobody likes a stinky engine. Or, it could be a cracked flexplate. I had that happen and it sounds exactly like you're describing. Since you'll have to pull the trans, you might as well have that LS standing by.
would my flex plate or Tc also cause my engine to crank slow when i try to start it?
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,281
Reaction score
6,278
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
would my flex plate or Tc also cause my engine to crank slow when i try to start it?
you saying the thign about the shifter is the exact thing you should be focused on, you said its not in neutral but it is park. the shifter is wobbly and doesnt feel proper.

Sounds like the shifter valve thing that controls the shifts and stuff in relation to the internals.. i would go under your truck and maybe give it a wiggle or disconnect the shifter and see how it moves one way and another. i dont know what it should feel like without the shifter in link, but it shouldnt be loosey goosy crunch crunch if that helps.
 

chevyfs

Full Access Member
Joined
Jan 21, 2022
Posts
55
Reaction score
17
Location
michigan
First Name
ray
Truck Year
1986
Truck Model
Chevy C10 Rwd P/U
Engine Size
4.3liter V6
you saying the thign about the shifter is the exact thing you should be focused on, you said its not in neutral but it is park. the shifter is wobbly and doesnt feel proper.

Sounds like the shifter valve thing that controls the shifts and stuff in relation to the internals.. i would go under your truck and maybe give it a wiggle or disconnect the shifter and see how it moves one way and another. i dont know what it should feel like without the shifter in link, but it shouldnt be loosey goosy crunch crunch if that helps.
it doesn't make a noise in park or neutral
 

AuroraGirl

Full Access Member
Joined
Sep 8, 2019
Posts
9,281
Reaction score
6,278
Location
Northern Wisconsin
First Name
Taylor
Truck Year
1978, 1980
Truck Model
K10, K25
Engine Size
400(?), 350
Is your TV cable adjusted properly? you said noises and stuff, and I realize your 4.3v6 probably has a 700r4. Is your carburetor stock?
 

Latest posts

Forum statistics

Threads
42,450
Posts
916,305
Members
33,980
Latest member
ruggedly
Top