Acts like it wants to run but doesn't.

NO4NSHIT

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I've got a 2003 Yukon XL it had a knock sensor code come up so I ordered knock sensors Delphi knock sensors GM wiring harness fel-pro gasket kit I didn't buy any of the cheap crap. Anyhow the day I got everything in it threw a code po300 which is multiple cylinder misfire. Tore the motor down that day. I cleaned intake cleaned fuel rails out come to find out I had water in my gas and I cleaned all the fuel injectors out checked everything made sure everything was good. Put it all back together it turns over but won't fire like I act like it wants to start but it doesn't start. I've checked everything made sure everything was plugged in I don't know what else to do
 

wjburken

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I've got a 2003 Yukon XL it had a knock sensor code come up so I ordered knock sensors Delphi knock sensors GM wiring harness fel-pro gasket kit I didn't buy any of the cheap crap. Anyhow the day I got everything in it threw a code po300 which is multiple cylinder misfire. Tore the motor down that day. I cleaned intake cleaned fuel rails out come to find out I had water in my gas and I cleaned all the fuel injectors out checked everything made sure everything was good. Put it all back together it turns over but won't fire like I act like it wants to start but it doesn't start. I've checked everything made sure everything was plugged in I don't know what else to do
Since you tore apart part of your fuel system, might double check all of that and make sure you have good fuel pressure.
 

NO4NSHIT

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Since you tore apart part of your fuel system, might double check all of that and make sure you have good fuel pressure.

Well I've just done that.. and realized my fuel pressure regulator is leaking a little bit popped it off and reinstalled it correctly now it started to start but was really crappy sounding and then died scanned it again and it came back with po200. Pressed the check valve on other side of fuel rail got nothing coming out of it. So no fuel pressure which is my problem but last night the fuel line that ran that runs from the fuel filter to like a some type of other valve or regulator whatever underneath the truck and then another line goes off of that up to the fuel rail with a small line from the fuel filter to that regulator whatever it is it screwed up on me and I couldn't get it off the filter and I realized that one of the little tabs on the inside was messed up so I replaced it with a piece of fuel line that I had and I had to make it a little bit longer of course because I didn't want me cuz it's not the same type of fuel line it's the same size but it's a little bit longer don't know if that really means much..
 

exp500

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Water in fuel can wreck everything in system. fuel pump suspect now.Check fuel pressure, clean out tank.
 

NO4NSHIT

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Water in fuel can wreck everything in system. fuel pump suspect now.Check fuel pressure, clean out tank.
I've cleaned out the tank blown out all the line cleared all water from fuel system. I've replaced the fuel pressure regulator spark plugs cuz they were fouled out. Replaced the knock sensors intake gaskets leaned the throttle body and fuel injectors. She starts up ran ok for about 10 seconds and then started running rough and backfiring out tailpipe so I then shut it off and am now at y'all mercy.. idk what To do... It didn't throw no codes so I'm confused on what is wrong..
 

NO4NSHIT

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So after I replaced the spark plugs I started it up and ran it for about 5 minutes and it started to run like shit then SES light started to flash and I shut it off rechecked the spark plugs started on number 1 it was ok but number 3 and 7 were black as night. I wiped 7 off so I could see weather I could clean it or not.. And number 5 had just a slight discoloration on it from looked to be like oil.. now I don't know jack shit bout the LS motors so please help me..
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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?
 

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
 

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
 

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