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Q: My firebird keeps reading po303 and jumps from po302 and po301 on 1999 Pontiac Firebird

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Just did a head gasket job all new wires and plugs.and replaced coil packs and new fuel filter and checked fuel pressure and all is good and to spec and cleaned the maf sensor..changed num 3 and num 2 sparkplug and now its reading misfire num 1..we need help with this one..we are stumped.
No car image 94a1663db56199c5353592009e34aaa51078a2469bed068bb8d6f0ba43accf97
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Is it actually misfiring or the ecm just thinks so? 3.8 or 5.7?? Compression, injector pulse, vacuum leak, you say spark ok right?
Its a 3.8 v6.spark is ok and no leaks we have found yet..and compression is ok it was throwing this coode before the head gasket change so the problem was there before we even touched it.
When it started is irrelevant, is it missing on those cylinders? Running rough, idling rough? Forget about codes for now! Get to them later.
Very slight rough idle..we took the num3 wire off to see if it would be worse of a idle and the car started and then just there any way ro test the ecm thats under the coil packs.
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