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350 misfiring - help please

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Old August 15th, 2021, 4:39 PM
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Default 350 misfiring - help please

Hi all

I have a ‘49 3600 with a late 80’s 5.7 350 engine and three speed box. The engine has MSD distributor and leads and dense t20-tt plugs. The engine runs ok but a little lumpy when stationary. When I drive it above 30 mph I start to get a terrible vibration through the whole truck. I’ve had the wheels balanced and they are perfect. I’ve had the propshaft rebuilt and that’s perfect so it can only be the engine or the transmission. Ive changed the plugs and leads this weekend and there has been no change.

The vibration is awful when it starts so I’m now thinking it’s a severe missfire. I do find that when it happens, if I drop it into 2nd gear and Rev the nuts off it, it goes much smoother - could this be load related?

Any help much appreciated.

Anthony
Tamworth, England.



Old August 15th, 2021, 5:46 PM
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Originally Posted by AnthonyW
Hi all

I have a ‘49 3600 with a late 80’s 5.7 350 engine and three speed box. The engine has MSD distributor and leads and dense t20-tt plugs. The engine runs ok but a little lumpy when stationary. When I drive it above 30 mph I start to get a terrible vibration through the whole truck. I’ve had the wheels balanced and they are perfect. I’ve had the propshaft rebuilt and that’s perfect so it can only be the engine or the transmission. Ive changed the plugs and leads this weekend and there has been no change.

The vibration is awful when it starts so I’m now thinking it’s a severe missfire. I do find that when it happens, if I drop it into 2nd gear and Rev the nuts off it, it goes much smoother - could this be load related?

Any help much appreciated.

Anthony
Tamworth, England.
Have you checked to motor gearbox mounts?
Old August 15th, 2021, 5:52 PM
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Get it up to speed where it vibrates badly and shift to neutral - see if it stops.
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