Error code P0303 cylinder misfiring

[bent]

My 1996 GMC 1500 Sierra overheated and blown out the back of the intake manifold gasket. Replaced gaskets but now getting a code P0303. Replaced rotor and cap also spark plug and wire for cylinder and getting spark. Idling rough but running good at speed. What else could be the problem?

Thank you for any help Brent

 

[Molson02536]

My 1996 GMC 1500 Sierra overheated and blown out the back of the intake manifold gasket. Replaced gaskets but now getting a code P0303. Replaced rotor and cap also spark plug and wire for cylinder and getting spark. Idling rough but running good at speed. What else could be the problem?

Thank you for any help Brent

Bad fuel injector system (bad poppet valve #3), here is a link that can explain better to you what the problem may be. Good luck.

http://members.shaw.ca/betterthanyoutoo/Sticking Poppet.htm

 

[bent]

Thanks molson, Is a shop only setup for this procedure?

Thanks Brent

 

[Molson02536]

Thanks molson, Is a shop only setup for this procedure?

Thanks Brent

Well you can first try running fuel injector cleaner through your system for the next week or two and see if that helps. Remove the #3 spark plug and inspect it's condition, see if the deposit left on the plugs indicate if it's running rich or lean. Which would indicate a poppet issue that would need to be replace.

You can buy the poppet nozzle individually, or the up graded MPFI system at NAPA, or Auto Zone and they will have the step by step instructions fory ou to replace the injection unit. Of course the GM Dealer can also replace your fuel injection system and do the up grade also.

Good luck and start with the simple and try to clean out your fuel system first, buy some Sea Foam and follow the instruction to clean out the upper intake and injectors by adding it in to your gas tank and in to your upper intake. Just follow the instructions.

http://www.seafoamsales.com/

 

[bent]

I never heard of Sea Foam cleaner. I looked at there site is it much better than other injector cleaners?