Acts like it wants to run but doesn't.

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exp500

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What is your fuel pressure and will it hold for 20 minutes? What code does it show? Can you see live data?
 
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NO4NSHIT

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So I've tried new coil pack on cylinder number one and still coming back with PO301 but it's weird because when it starts it will idle decently smooth you can still tell that there's a miss but not bad then in about 10-20seconds it will start idling rougher and start missing bad and then backfiring out exhaust but if you press the gas it'll sound like it kinda goes away a lil bit but still backfires.. I have new injectors on the way
 
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NO4NSHIT

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What is your fuel pressure and will it hold for 20 minutes? What code does it show? Can you see live data?
I don't know fuel pressure yet I'm going to check that tonight hopefully the fuel pressure and vacuum tester my pops got from harbor freight will work. I can't keep it running for more than 3 minutes without it backfiring out exhaust. It shows a p301 code but the scanner I have doesn't show live data
 

rockola1971

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Did you try clearing all codes then starting? Doublecheck all sensors and make sure you plugged them all in to their wiring harness.
 

drakon543

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injector could definitely be a possibility with above stated symptoms. if that injector is trying to hard and clears up a bit when you open the throttle giving it enough air to burn the extra fuel out could be the case. what looked like oil can just be excessive carbon build up from a bad burn with a coating of wet gas. next time to try to run it and pull the plugs again hit that wet plug with a lighter. if it instantly catches on fire its definitely just wet with gas and flooding that cylinder.
 

Doubeleive

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injector harness could be a problem also, just food for thought and I would check the ecm harness, be sure it is clean and dry with no corrosion.
 
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NO4NSHIT

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It's a 2003 Yukon XL 5.3 l Vin Z. I've already replaced all the fuel injectors new plugs and wires, mass air flow sensor, O2 sensors. It will idle smooth for probably about 30 to 45 seconds then start to slightly miss, then it would start to backfire like every 10 seconds it would hit a backfire. It threw up a po300 and a po301 and then a po171. I just performed a fuel pressure test on it it went up to about 46 PSI and then slowly began to drop I was just curious that would that be a bad fuel pump I don't know how long it's supposed to hold and you can't trust everything you read on Google..
 

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