Error Code P303 [Archive] - Forum


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09-29-2004, 05:00 PM
Hi all!

I have this on again off again SES light. :rolleyes: Each time it comes on again it reads a P303 code - Cylinder 3 Misfire. My trusty mechanic (and he really is) has checked the plugs, wires, and everything ignition related and all seems fine.

Question is this - Is there something, either subtle or quite obvious that we may be missing? He (and I) would rather not just have him go on a hunch and start replacing injectors or whatnot. That would get expensive fast. I have run injector cleaner theought the car twice with no difference.

The car has 102.000 miles, runs well, and there is no noticable loss of power. Occasionally it hesitates when you hit the throttle, but then is fine again. Any ideas would be appreciated.

Thanks in advance,

09-29-2004, 05:14 PM
It's most likely an injector. Every 3100/3400 with a misfire and ignition checks fine, it's been an injector. Those injectors clog up real easy.

09-30-2004, 09:17 AM
Get some fuel injector cleaner and run that through the system (not the fuel tank kind, the one you hook directly up the fuel rail) before replacing a possibly clogged injector.


09-30-2004, 06:10 PM
Where do I get the? Does that require special tooling?



10-01-2004, 07:50 AM
Yeah, you do need a special tool for it. It's basically a canister to hold the cleaner (GM Top Engine Cleaner)/gas mixture and it has an air fitting with regulator to pressurize it. You hook it up to the gauge port on the rail and block/clamp the supply and return lines (so it's only getting the cleaner mix). Any GM dealer has it and probably independent shops too.

10-01-2004, 07:28 PM
Great, thanks fo rthe information!!


10-10-2004, 03:46 AM
new plugs can sometimes be defective,switch # 3 plug with new one it worked for me.

10-19-2004, 06:39 PM
got the injectors cleaned the Pressurised way...seemd better now. 2 days with no codes so far :-) If it returns will try the plugs.

Thanks agan for the responses