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Here's a useful tip for you. Sell the gto and buy a kia.

Then you can run whatever you want in the engine and you won't be killing a unicorn in the process.
 

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Sponsored by seafoam? Do you wash your clothes with it?

Ever since I added Svede OTRCAI I can hear a thump when I shut the car off.
Or maybe my engine or motor mounts are blown. :dunno:

Comp test shows nothing to be concerned about.
 

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I have a 04 GTO LS1 engine and it's only seen 55K miles. Just today I finished a 30 mile drive and upon turning my engine off in the driveway, I heard a "thump thump" sound just as the engine finished its last turn. I was alarmed so I turned it on and shut it off again. The same "thump thump" sound came from the engine as it shut down. I tried it again, and I only heard one "thump". Again, and only heard it once.

On a normal basis this engine runs beautifully, and still has great gas mileage despite my occasional lead-foot joyriding. With oil changes, I always give it valvoline full synthetic 5w-30 oil with a half can of sea foam and a full bottle of Lucasoil synthetic oil additive in the oil pan. The problem can't be because of poor upkeep...

My dad's saying it's a timing problem, and eventually that my engine will do something called 'dieseling' where it'll start turning in reverse when I shut the engine down. Is this true?
Moreso, what in tarnation would I do to fix it?

Thanks ya'll.
I have a 04 GTO LS1 engine and it's only seen 55K miles. Just today I finished a 30 mile drive and upon turning my engine off in the driveway, I heard a "thump thump" sound just as the engine finished its last turn. I was alarmed so I turned it on and shut it off again. The same "thump thump" sound came from the engine as it shut down. I tried it again, and I only heard one "thump". Again, and only heard it once.

On a normal basis this engine runs beautifully, and still has great gas mileage despite my occasional lead-foot joyriding. With oil changes, I always give it valvoline full synthetic 5w-30 oil with a half can of sea foam and a full bottle of Lucasoil synthetic oil additive in the oil pan. The problem can't be because of poor upkeep...

My dad's saying it's a timing problem, and eventually that my engine will do something called 'dieseling' where it'll start turning in reverse when I shut the engine down. Is this true?
Moreso, what in tarnation would I do to fix it?

Thanks ya'll.
I know this post is old but I am literally having this same problem. Did you so happen to fix it?
 

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7 years later the advice would still be the same. Dont try to start it and find out if it's broken. Get it to a qualified mechanic!!!! It could be anything and it's impossible to guess without running tests on it
 
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