Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

1989 Oldsmobile Cutlass Supreme knocks when accelerating

When I accelerate the car starts knocking – like it’s missing. Could the transmission be going out? Points and plugs seem okay.

If you are hearing that knocking sound from the engine under acceleration, first thing I’d do is get the spark plugs and wires replaced. If the knock persists, try a couple tanks full of high octane ( premium) fuel. If that makes it better, have your ignition timing and your EGR system checked. Next step would be a bottle of Seafoam administered through the throttle body to decarbonize the combustion Chambers and pistons.

Thank you. I will work through the list:

My 1984 Chevy Cavalier did that. The problem went away when I used premium. I put Marvel Mystery Oil in the regular gas for a few tankfuls and the problem went away. I think there were carbon deposits and the MMO dissolved them and the carbon went out the tailpipe.

My 1984 Pontiac Sunbird also did that. Mid-grade gas was rare at the time, except at Sunoco stations, so I’d put in half regular and half premium.