Hello, i have a 97 chev P.U. 5.7 throttle body. it is miss firing on didernt cylinders??? I have replaced plugs,wires,cap,rotor and coil and...

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Hello Jimmy... how are you doing?

Is this a rebuilt engine Jimmy?

Hi Jimmy... may I ask if the injectors are working properly? A failing fuel injector can cause a misfire Jimmy. Try to remove the injectors and check if it will spray when you crank the engine

Thanks Jim... As a first course of action go and check the fuel injectors first if it will spray fuel. This is common and it can be the cause.

I see, other cause of this is fuel starvation which usually occur when you have a failing fuel pump. It will be best if you have a good fuel pressure Jimmy.

It can be both Jimmy. There are times that the misfire occur on the same cylinder but there are occassions that it will be random. If it occurs in the same cylinder it is an injector failure. If it's random, it can be fuel starvation which can be cause by a failing fuel pump or fuel regulator

May I ask the exact model of your Chevy  Jimmy

No you dont have to Jim... It should play between  52 to 66 psi. Please click the blue link below named FUEL PRESSURE just to have a reference on how to check the fuel pressure. I'll be standing by

FUEL PRESSURE

Have you checked it Jim? Is there anything else I can add or help you with?

Yes indeed Jim... if everything else is good I believe that it's time to check the valve clearances. If the gap is off then that's the cause of misfires. May I ask you a little favor before we get done Jim?

I have an another idea.. Try cleaning your MAF sensor, it can be full of carbon which can cause a misfire. If cleaning doesn't help then try to replace it. All of the necessary parts have been replaced and the MAF can be the culprit. 

Dear Jim, It was a pleasure helping you with your CHEVROLET issue today. Here is a summary of the resolution.

Issue identified : Engine misfire
Solution Implemented : Fuel pressure must be checked as well as the MAF sensor since every necessary parts have been replaced.
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That's great fuel pressure Jim... try to check the vacuum lines as well and replace worn out ones.