Q: Car sputters and backfires under load

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I have an 88 mustang with a new cam, springs, coil, distributer, fuel pump, spark plugs, wires, timing chain and I'm having a sputter problem if I go over 3500 rpm and if I keep pushing it it will backfire. Then when u let rpms come back down it continues to sputter till u turn car off and back on. Then it's good till u go over 3500 rpm again?

My car has 292000 miles.
My car has a manual transmission.

This sounds like one of the valves are sticking or a spring is weak or broken. You may also have a lifter that is holding the valve open after you go to 3500 rpm and will continue to hold open the valve until you shut off the engine and oil pressure gets off the lifter. You may have to check the push rods and lifters for clogged passages. If you would like to have this checked in person, an expert from YourMechanic can come to your car’s location to diagnose the sputtering issue and determine what repairs are needed.

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