I just poped in a new used blocked in my truck....

Now at when it starts ( like cold starts ) it back fires....??????

I dont have a clue at what to do ...

This just happens at when it sits for awhile, but at when it warms up no problem afterwards.....

Can anyone help......

Do you know how many miles are on this engine? Usually a backfire is related to timing, either in the valve train or ignition timing. A worn or flat cam can run rough and maybe cause a backfire. Sticking valves won't open and close as they should and cause a backfire that might clear up when warm... I'd check all the basics, and then look deeper. A vacuum gauge on the intake will tell you all about the status of the valve train. Good luck.

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86 ranger 4x4 2.3l efi gas non turbo 5 speed. Small lift. 2.25 in exh w/turbo muffler, no cat or egr. New cam, lifters, rocker arms (stock grind). New fuel pump in tank.

Was told that the engine had 62 xxx miles on it when i bought it to replace the one that was in it....

That is confusing. I agree. I would check all the basics, timing belt, ignition timing (with a timing light), check to see that the pcm is controlling the advance correctly... other than that, hope you got a good engine.

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86 ranger 4x4 2.3l efi gas non turbo 5 speed. Small lift. 2.25 in exh w/turbo muffler, no cat or egr. New cam, lifters, rocker arms (stock grind). New fuel pump in tank.