Recently bought a 03 monte carlo LS 3.4. Within days it over heated. Replaced thermostat, radiator, waterpump, intake gaskets, head gaskets, and checked to make sure heads were not warped or cracked. Once repaired and ready to go it had a bad miss. We changed sparkplugs and wires but still a miss. The check engine light comes on and blinks once you start driving it. It seems to miss when it is idling in park also but the check engine light does not come on until you are driving. What could this be? Any help PLEASE!

 

Ok AutoZone just checked and said it could either be the number 3 injector staying open or it could be an o2 sensor setting it off?
If it is the injector they said I might as weel get a new engine. Is that true or can it be fixed?

 

No, just get a new injector or get #3 cleaned.

 

The spark plug wires were put back on in the correct place right?

 

First, what code did AutoZone pull?

Second, I assume as John asked, plug wires/firing order was checked?

Third, did you use new injector O-rings? Verify the fuel rail is seated properly? Given where the rail is, you have to pop the UIM to check it. You might be able to mist starting fluid and get a feel if it's a badly seated injector.

Forth, if you used BOSCH plugs, rip them out, replace with NGK or AC Delco.

That's the top list of things (in order of my thoughts without knowing the actual code).