Q: Misfire happens at 1500 rpm's.

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so I bought the car for 650 dollars and it had a really bad misfire so I changed all the plugs and coil packs and it seemed to help it significantly but it still has a miss fire at 1500rpm and smooths out in higher rpm. I did a block test yesterday and the fluid stayed blue (I ran the test for 15min) can't say for sure what coolant was used prior but I'm running blue devil coolant flush in it rn.

My car has 170000 miles.
My car has an automatic transmission.

Hi there. Check the fuel injectors one at a time by disconnecting the harness and see if the engine stumbles or not. If the engine stumbles when the injector is turned off, then the injector was working. If the engine did not stumble when turning off the injector, then either the injector is not working or there is a more severe issue with the cylinder. You also can get a noid light and test all of the injectors for firing. If they all turn on, then put a compression tester on all of the cylinders and check the balance of the engine. Any cylinders that are low on compression, check them with a leak down tester (requires compressed air) and see what the leak percentage is and where the leak is coming out at. It is common to have a burned valve. If you need further assistance with your engine misfiring, then seek out a professional, such as one from Your Mechanic, to help you.

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