HELP Please!!!

[JC1999Yukon]

OK here's the background have a 1999 Yukon with 350 Vortec 4wd and was getting a P0303 code (#3 cylinder misfire). So here is what has been done Cats, Fuel Pump, MAF, Cap, Rotor, Wires, Plugs 14 months ago, Crank Sensor, Air Filter 6 months ago, Intake Gaskets, #3 Fuel Injector, Plugs, Coil, set timing to 0 degrees 2 weeks ago. Now I still get a random P0303 (#3 cylinder misfire) or a P0300 (Radom cylinder misfire) and a P0430 (Catalyst System Efficiency Below Threshold (Bank 2)). I am out of clues. Anyone with any help, ideas, even guesses.

Thanks, JC

[foreverfalcon40]

Well I hope its not your case.

I had a misfire #5 and caused 3 and 7 to misfire. I ended up needing my heads rebuilt.

[hapyspaz]

Have you switched over to the new fuel injection system or replaced the fuel pressure regulator?

[clean454]

check ur maf sensor, if its clean, i didnt let my k &n filter dry all the way and the oil got all over the filter, and it threw all kinds of codes just like urs...

[JC1999Yukon]

Thanks for input so far. I did not switch over to the "new" fuel injection system just replaced #3 injector was hoping that was it and would not have to go with the remote injector system. I checked the fuel pressure at idle it was a constant 57 lbs and under load with rpm's about 1500 it was nearly always 60 lbs it never dropped below 55 lbs the entire time I had the gauge on it. I have not done a compression test on the engine yet, gonna borrow a compression gauge and see what I get. The truck runs GREAT except for it pulling codes. Almost forgot the MAF is nice and clean just like when I put it in.

[ravingmadman]

I don't have anything really good to say other than it seems to me that the P0430 (Catalyst System Efficiency Below Threshold (Bank 2)) code might not be related? Don't know if that helps? :shrug:

[clean454]

did u take the plug out and look at it?