# 1989 Oldsmobile Cutlass Supreme knocks when accelerating

**URL:** <https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194>\
**Category:** Maintenance/Repairs\
**Tags:** oldsmobile, cutlasssupreme\
**Created:** [December 7, 2019, 2:25am UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194 "2019-12-07T02:25:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![bohasha](https://avatars.discourse-cdn.com/v4/letter/b/b5e925/32.png) [@bohasha](https://community.cartalk.com/u/bohasha)\
**Post date:** [December 7, 2019, 2:25am UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194/1 "2019-12-07T02:25:02Z")

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

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**Author:** ![old\_mopar\_guy](https://avatars.discourse-cdn.com/v4/letter/o/6bbea6/32.png) [@old\_mopar\_guy](https://community.cartalk.com/u/old_mopar_guy)\
**Post date:** [December 7, 2019, 3:18am UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194/2 "2019-12-07T03:18:36Z")

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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.

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**Author:** ![bohasha](https://avatars.discourse-cdn.com/v4/letter/b/b5e925/32.png) [@bohasha](https://community.cartalk.com/u/bohasha)\
**Post date:** [January 11, 2020, 5:20am UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194/3 "2020-01-11T05:20:08Z")

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Thank you. I will work through the list:

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**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\
**Post date:** [January 11, 2020, 6:11pm UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194/4 "2020-01-11T18:11:54Z")

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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.

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**Author:** ![davepsinbox\_157004](https://avatars.discourse-cdn.com/v4/letter/d/73ab20/32.png) [@davepsinbox\_157004](https://community.cartalk.com/u/davepsinbox_157004)\
**Post date:** [January 11, 2020, 9:46pm UTC](https://community.cartalk.com/t/1989-oldsmobile-cutlass-supreme-knocks-when-accelerating/154194/5 "2020-01-11T21:46:18Z")

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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.