light knock at neutral throttle
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Junior User
Joined: Oct 2003
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From: Whitehorse, Yukon, CAN.
light knock at neutral throttle
Howdy,
I just picked up a '78 bronco and drove it 1200 miles to where i live. after i got home i noticed what i first thought was a rattle but then realized that it was a light knock that would go away if i got on or off the gas. i can't hear anything at idle but now that i hear it it seems very noticeable.
i'm hoping it's not bottom end but that is my suspicion
. it is definetely in time with the engine. the engine is high mileage but is still a drag as i don't want to have to rip the engine out of something that ran like a top for the trip home.
any ideas, if the engine is pooched i think i'd like to replace it with a 460. any opinions here.
tia
Bob
I just picked up a '78 bronco and drove it 1200 miles to where i live. after i got home i noticed what i first thought was a rattle but then realized that it was a light knock that would go away if i got on or off the gas. i can't hear anything at idle but now that i hear it it seems very noticeable.
i'm hoping it's not bottom end but that is my suspicion
. it is definetely in time with the engine. the engine is high mileage but is still a drag as i don't want to have to rip the engine out of something that ran like a top for the trip home.any ideas, if the engine is pooched i think i'd like to replace it with a 460. any opinions here.
tia
Bob
Elder User
Joined: Sep 2003
Posts: 908
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I have a very similar sound in my high mileage 400, and suspect it's a wrist pin. The pin floats at neutral throttle.
When they get worse, they will knock more when you get on or off the gas, as now the pin is really loose.
I don't know for sure that's it, but it's what I suspect.
How is your oil pressure? Any metal filings visible on the dipstick when you pull it?
When they get worse, they will knock more when you get on or off the gas, as now the pin is really loose.
I don't know for sure that's it, but it's what I suspect.
How is your oil pressure? Any metal filings visible on the dipstick when you pull it?
Freshman User
Joined: Feb 2003
Posts: 27
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From: Alberta
I have almost more of a ticking in my 400 at idle, it sounds like a lift but they are almost new. We changed them thinking thats what it was but nothing changed. It doesn't burn any oil and there is no metal filings in the oil. Oil pressure is really good also. Any clues? Would be great
TMK
TMK
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Junior User
Joined: Oct 2003
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From: Whitehorse, Yukon, CAN.
Originally posted by scroob
I have a very similar sound in my high mileage 400, and suspect it's a wrist pin. The pin floats at neutral throttle.
When they get worse, they will knock more when you get on or off the gas, as now the pin is really loose.
I don't know for sure that's it, but it's what I suspect.
How is your oil pressure? Any metal filings visible on the dipstick when you pull it?
I have a very similar sound in my high mileage 400, and suspect it's a wrist pin. The pin floats at neutral throttle.
When they get worse, they will knock more when you get on or off the gas, as now the pin is really loose.
I don't know for sure that's it, but it's what I suspect.
How is your oil pressure? Any metal filings visible on the dipstick when you pull it?
oil pressure seems a little low to me (between the o and the i on the stock guage, up around the L on first start of the day @ -3).
haven't noticed any filings but i'm going to change the oil soon so i'll keep my eyes open.
how long has your engine been making this sound?
see ya
Bob
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Junior User
Joined: Oct 2003
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From: Whitehorse, Yukon, CAN.
Originally posted by Bill_Beyer
If it's a wrist pin you should be able to 'short it out' by removing the spark plug wires 1 at a time until the knocking stops.
If it's a wrist pin you should be able to 'short it out' by removing the spark plug wires 1 at a time until the knocking stops.
thanks for the tip, i'm going to poke around with a stethescope to see if i can hear it at idle, if so i'll try your idea.
see ya
Bob
Elder User
Joined: Sep 2003
Posts: 908
Likes: 4
When I bought the vehicle, there was a discernable "wop wop" sound at cold idle, which went away after the engine warmed up. I figured that was piston slap. I eliminated the usual suspects by starting the engine with all the belts and fuel pump off. A fuel pump can make that same sound.
I drove the vehicle across country and back in summer 2002. Because of my basic laziness in prepping for the trip, I failed to change a certain $5 part and found myself halfway across with a very hot motor and a blown head gasket. When I pulled the thermostat, it was the original factory unit. Ouch.
When I got to my destination, I pulled the head to replace the gasket, and noticed a scratch in the #5 cylinder wall corresponding to the position of the wrist pin.
The rapping began shortly after getting home. It was very faint at first, and sounded just like a slightly flat lifter. You only hear the sound at neutral throttle, like you described. The best time to hear it is at about 50 MPH just as you top a hill and let off the gas.
It has gotten worse. I suppose if I continue to drive it, it will someday reveal itself.
I drove the vehicle across country and back in summer 2002. Because of my basic laziness in prepping for the trip, I failed to change a certain $5 part and found myself halfway across with a very hot motor and a blown head gasket. When I pulled the thermostat, it was the original factory unit. Ouch.
When I got to my destination, I pulled the head to replace the gasket, and noticed a scratch in the #5 cylinder wall corresponding to the position of the wrist pin.
The rapping began shortly after getting home. It was very faint at first, and sounded just like a slightly flat lifter. You only hear the sound at neutral throttle, like you described. The best time to hear it is at about 50 MPH just as you top a hill and let off the gas.
It has gotten worse. I suppose if I continue to drive it, it will someday reveal itself.
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Senior User
Joined: Apr 2003
Posts: 270
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From: columbia
My 78 f150 nocks slightly at idel I thought that a piston wasn't firing but by listening to it, it sounds like all 8 are firing sounds good though and nocking goes away when I rev it up hope it aint serious.
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Thread Starter
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Junior User
Joined: Oct 2003
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From: Whitehorse, Yukon, CAN.
Howdy,
well i pulled the valve covers the other night and took off all rocker arms and pushrods, everything looked ok. the pushrods were straight and the only trouble i saw was a spot of pitting on the fourth rocker arm back on the drivers side. it is on the valve end of the arm and meakes up about half of the area that rides on top of the valve.
reinstalled everything and retorqued the bolts to haynes manual specs. knock is still there. think i might pull fuel pump next . i crawled all over the motor with a stethescope at idle and couldn't hear any obvious noise. really trying to avoid pulling the oil pan to look for bottom end trouble. guess i'll just drive it if i can't pin it down.
see ya
Bob
well i pulled the valve covers the other night and took off all rocker arms and pushrods, everything looked ok. the pushrods were straight and the only trouble i saw was a spot of pitting on the fourth rocker arm back on the drivers side. it is on the valve end of the arm and meakes up about half of the area that rides on top of the valve.
reinstalled everything and retorqued the bolts to haynes manual specs. knock is still there. think i might pull fuel pump next . i crawled all over the motor with a stethescope at idle and couldn't hear any obvious noise. really trying to avoid pulling the oil pan to look for bottom end trouble. guess i'll just drive it if i can't pin it down.
see ya
Bob