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

Spartanzz

Spartanzz

New member
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
 


Spartanzz said:
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
Click to expand...

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.
 
ok wellthe other thing is it did go off for a tad after a while of relaxed driving but came back after i did go wot. the other thing is the car idols perfectly fine other than the rattle i have from the supercharger coupler i need to replace so i wouldn't think it would be a big leak iv checked the coil and it does give off a spark but i have to check the plug on it. also just have to check myself on this but am am i right on the middle cylinder on the front of the engine being cylinder 3? thats the one thats saying is misfiring and i also have a friend who swares that the upstream O2 sensor is whats causing both error codes...
 
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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.
 
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