Thread: Need help finding out what i need to fix! P0303 and P0171 codes

So i have had my Grand prix GTP for a few weeks now and we have been trying to find out what should be replaced to make the two codes i have go away. The codes came on after i went WOT and then let off and the codes are P0303 Cylinder 3 misfire and P0171 system too lean. I have been told many things like i should replace my plug wires and plugs, i should search for a vaccume leak somewhere, and also that i have a lazy upstream oxygen sensor. so i am wondering if any of you all have had this problem and could help me find out what i have to replace to make the codes go away so i can get an emissions test done soon. Thanks

Originally Posted by Spartanzz

So i have had my Grand prix GTP for a few weeks now and we have been trying to find out what should be replaced to make the two codes i have go away. The codes came on after i went WOT and then let off and the codes are P0303 Cylinder 3 misfire and P0171 system too lean. I have been told many things like i should replace my plug wires and plugs, i should search for a vaccume leak somewhere, and also that i have a lazy upstream oxygen sensor. so i am wondering if any of you all have had this problem and could help me find out what i have to replace to make the codes go away so i can get an emissions test done soon. Thanks

With any misfire, check spark plugs, wires and coils. If you have P0171, you probably have a big vacuum leak. Do you have access to a scanner? If so, scan your IAC values at idle (after car is warm). They should be between 45 and 55. 01gpgt01 gave me this tip, and I found my vacuum leak an fixed my P0171 code. Also, scan your O2 values. That will indicate if there is a problem there.

Umm...

This sounds like your stereotypical piston chipped scenario.

WOT + lean = misfire code?

Pull the plug and hope its not bent.

Originally Posted by matt5112

Umm...

This sounds like your stereotypical piston chipped scenario.

WOT + lean = misfire code?

Pull the plug and hope its not bent.

Never thought of that. Matty boy, you're so smart. Haha.

bad upstream messes things up.

Have you pulled the plug yet?

It could be a bad wire or something simple like that.

Front middle is #3.

yes he says its the upstream o2 sensor throwing the codes and causing this mis fire. And i havent pulled the plug just yet going to do it tomorrow once i have a second.