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Where to start with a motor knock

buckmtn

buckmtn

1/2 ton status
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Oct 17, 2005
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Stokesville,Va
My 89 tbi 350 has developed a knock. Upon initial start up it will knock for maybe 5 seconds then it goes away. While idiling it sounds fine. Crussing down the road it sounds fine. Go offroad and try to climb something and getting into the throttle the knock come back and is constant while on the gas. Oil pressure seems fine, no smoke from tailpipe. Where should I start?
Sounds as though its coming from left side of motor but not positive.
 
Ya sure its a KNOCK , not a tapping or ticking sound. It could be main bearings. You could jus pull oil pan, pull oil pump, and pull rod caps and inspect the rod bearings for unusual wear.
 
Sure sounds like a knock to me. Not of the valve tapping or pinging sound. Added some Lucas oil to it but haven't got to drive it yet.
 
Auto transmission? flywheel bolts can work loose and make that noise. But you need to look and not try to bandaid it with oil. Most time you can save a engine by just replacing the bearings. easy to do with engine in. If its the converter then you might get away with just tighten the bolts.
 
Well Lucas did not work. Suprise, Suprise!! I did notice that it does make a slight constant knock when idling. Manual transmisson not auto. Anyway to distinguish this from coming from the valvetrain or the bottom end? Probably end up having to take to someone that know more about it than I do. To change those bearings you'd have to pull the motor would't you. It seems to run fine. No loss of power, oil leaks, smoke just this noise. Any more ideas.
 
Mine has a slight knock when it's cold. It go's away after 2-3 minutes and has done so for about 8 years.

It doesnt smoke at all. 286473 miles on original motor:D
 
Take a broom handle and stick it to parts of the motor while running and put it to your ear. (make sure you dont loose a body part) You will hear where it is coming from easy then. And no you can replace all the bottom end bearings without pulling the motor. just drop the oil pan. But if the bearing surface is messed up you will have to remove motor. I have raced on a engine that made noises and when I got home pulled them down and it was totally screwed up. You will start loosing oil pressure when the mains go.
 
try running some fuel system cleaner that cleans the upper cylinders. I like Lucas, Red Line, or ACES IV.

On top of that run the next higher grade of gas and see if the knock goes away.
 
Sounds like detonation. Check and make sure your knock sensor wire is still hooked up (passenger side of engine in front of starter at pan rail). If the wire is disconnected hook it back up. If it is connected i would start by checking your base timing (should be zero with the EST wire disconnected). If base timing is correct then i would replace the knock sensor and go from there. The fact that you said it starts to make this noise when you start to climb something and doesn't stop until you let off the gas is detonation for sure.
 
4X4HIGH said:
Sounds like detonation. Check and make sure your knock sensor wire is still hooked up (passenger side of engine in front of starter at pan rail). If the wire is disconnected hook it back up. If it is connected i would start by checking your base timing (should be zero with the EST wire disconnected). If base timing is correct then i would replace the knock sensor and go from there. The fact that you said it starts to make this noise when you start to climb something and doesn't stop until you let off the gas is detonation for sure.
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x2!
 
Checked knock sensor wire and was good. Went ahead and replaced knock sensor, no help. Haven't checked timing. After timing check should I check plugs and compression check next? At idle don't here it very often. Mostly at around 1/4 throttle when revving in neutral. Then when offroading when getting into the gas to climb something. Sort of hard to describe to someone over the internet.
 
Definately sounds to be detonation. Check the timing next and also see if there are any codes set. I could be that the ESC module isn't working correctly and therefor not retarding timing when it really needs it.
 
merace19 said:
Take a broom handle and stick it to parts of the motor while running and put it to your ear. (make sure you dont loose a body part) You will hear where it is coming from easy then. And no you can replace all the bottom end bearings without pulling the motor. just drop the oil pan. But if the bearing surface is messed up you will have to remove motor. I have raced on a engine that made noises and when I got home pulled them down and it was totally screwed up. You will start loosing oil pressure when the mains go.
Click to expand...

Don't use the broom handle trick on the valve covers, oil pan or timing chain cover, doing that will give you noises from all over the engine. Try it on the front of the head or side above the exhaust, try the corner, front or side of the block. try to stay away from the fuel pump area if manual.

Should be very accurate for you if done right.
 
Another thing it could be is piston slap. That would explain why you hear it on start up. It makes the noise untill everything heats up enough to expand and then it goes away. Plus under hard exeleration it put enough force on it to come back. I just had my motor rebuilt and it started making a knocking sound for about the first 30 seconds and then it fades away. I took it to the engine builder and he told me that it sounded like piston slap, so now I have to pull my motor back out for him to fix it:mad:.
 
I would have to agree with you on the piston slap idea. I've heard that piston slap noise from a two stroke before and this seems very similar. Hope to have some time this weekend to investigate further. Thanks to everyone for their help.:D
 
Also do a google or search here for Seafoam.. Went through the same problem with my 90 and the stuff cleared it up!
 
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