Question about 1999 Chevrolet Silverado 1500

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I own a 96 chevy k1500 5.7 l vortec and have a no 5 cyl misfire

I own a 96 chevy k1500 5.7 l vortec and have a missfire on no 5 cylinder. i changed cap and rotor plugs, wires, compression is 150 psi, no vac leak, also done a induction clean, the ck engine light sometimes flases and other times on steady. sometimes it the light shuts off. misfire is worse when cold and subsides when warm. scanned code po300 any ideas?

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  • jammin777 Feb 04, 2010

    but it only has throttle body injection would that cause all cyl to missfire?

  • jammin777 Feb 06, 2010

    thanks yes a spider assy with poppet valves. i havent decided if i am going to replace the one poppet or upgrade the whole assy but for now i going to see if running sea foam in my tank will clear it up, thanks again for your help and will let you know what happens.

  • mark
    mark Jan 15, 2014

    lower intake gasket went out on my 97 caused miss fire code just like yours/cost a lot befor we found it !!



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It could be a faulty fuel injector, try running a fuel injector cleaner through your fuel system. At worst the poppet nozzle has gone bad and will need to be replaced, you can buy the poppet nozzle it self individually at Auto Zone or buy upgrade MFI system which is much better and less pron to fuel leaking room a cracked poppet line or nozzle which will cause what you have described.

Posted on Feb 03, 2010

Testimonial: "very helpfull, allthese year i thought i had throttle body as it turns out i have muti port. thanks for the fix."

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  • Harvey N Tawatao
    Harvey N Tawatao Feb 04, 2010

    NO the 1996-1998: Sierra; 8 Cyl 5.7L; "GAS, FI, VIN R" has a SCPI FUEL INJECTOR system, If you don't have that system then your have a 1993 to 1995 V8 engine and running a no Vortec with the Throttle body set up. Post me back on what year your Sierra is and if your not sure what's the 8th digit on your Vin number. R you have the Vortec V8 and the engine has the SCPI fuel injector system and if you have Z then you have a Throttle body. Good luck and let me know what engine you have, be gladd to help you get your engine running 100%

  • Harvey N Tawatao
    Harvey N Tawatao Feb 05, 2010

    You welcome, you don't have the Multi port in your truck. But there is the upgrade to replace the SCPI injection in there now. It's like a multi port in a way but there is no fuel injector at the end of the poppet line, just a valve which is common to go bad or carbon up. That is why GM started make the multi port again in 1999 for your truck, the main difference is there is a fuel injector at the end of the poppet line instead which is more reliable. Good luck and hope it's a simple bad plug instead of a bad poppet line. Keep me posted, would like to know your truck is running 100% again soon.

  • 58chevynutt Mar 03, 2011

    Does this come with everything I need to replace the injection in my 97 chevy k1500 5.7 vin.R? you mentioned poppet valve is this the whole setup or do I need more.thamk you


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I had a similar problem with a vortec. cause was faulty intake gaskets. The plastic gaskets sag in the middle over time and allow air between the intake and head. Felpro makes a steel/rubber replacement that is much better. hope that works for you.

Posted on Mar 01, 2010

Testimonial: "thanks it turned out to be an intake gaskit it runs great now! you are right the left bank gasit sagged as you mentioned."

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