Misfire after engine re-install, need advice
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From: Fuquay Varina, NC
Misfire after engine re-install, need advice So long story short, my LS1 hydro-locked a few months ago and bent a rod. Rod, piston, bearing, head studs, and all gaskets were replaced. Everything else checked out ok. Me and a friend did all the engine removal and install ourselves, while the internal engine work was done by Dusty at Blazing High Performance.
When we first fired her up again, it was on open headers. Thanks to my lack of experience/knowledge whatever you want to call it, left the O2 sensors in while it was running on open headers for maybe 10 minutes. It burnt them up leading to a SES light. Had a misfire at idle (seemed to be only or more so when it was warmed up or under load). Got it checked, sure enough it was both O2 sensors with a misfire code. Then the SES light disappeared the next day (we installed the y pipe the next day). So I replaced the O2 sensors and checked the spark plugs. All the plugs looked nearly brand new (replaced maybe 6 months ago), no buildup or anything on them.
Now while it seems to be running smoother and from what I can tell it is misfiring less than it was before, it still does it while idling at operating temp (makes a "putt" sounding noise every once in a while) and when I give it heavy throttle (about 75%, haven't gone WOT yet) you can feel it stumble/choke up a bit. What could be the cause of this and what do I check next?
When we first fired her up again, it was on open headers. Thanks to my lack of experience/knowledge whatever you want to call it, left the O2 sensors in while it was running on open headers for maybe 10 minutes. It burnt them up leading to a SES light. Had a misfire at idle (seemed to be only or more so when it was warmed up or under load). Got it checked, sure enough it was both O2 sensors with a misfire code. Then the SES light disappeared the next day (we installed the y pipe the next day). So I replaced the O2 sensors and checked the spark plugs. All the plugs looked nearly brand new (replaced maybe 6 months ago), no buildup or anything on them.
Now while it seems to be running smoother and from what I can tell it is misfiring less than it was before, it still does it while idling at operating temp (makes a "putt" sounding noise every once in a while) and when I give it heavy throttle (about 75%, haven't gone WOT yet) you can feel it stumble/choke up a bit. What could be the cause of this and what do I check next?
Last edited by ncfastls1; Oct 10, 2011 at 06:49 PM.
When you had it apart did you have any marks on the tops of the piston from any of the valves? Might have a slightly bent valve. I would start with doing a compression test of all eight cylinders,with all the spark plugs taken out first.Pull the relay for the fuel pump first,to keep the cylinders empty of fuel.
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I did not see it when the engine was apart, but I asked Dusty to check over everything to make sure nothing else was damaged, and he said he did not see any problems other than the bent rod. He replaced the head gaskets so he had to have the heads off and looked over them. I have the bent rod with piston and I see no abnormal marks on the top, just normal combustion.
Holy Crap, i dont know if I have ever gone into a thread and seen someone from the same city..... Good luck, if you need any help I am a tech and know these engines well. Another option would be to swing by Mezzacappa Motors directly across from the licsence agency and tell him Mark sent you! Im sure ill see you around, ill be the one in the Porsche that doesnt sound quite right!
Mark
Mark
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From: Fuquay Varina, NC
Well I got the codes read in the shop today. P0300 random misfire and P1153 air/fuel metering bank 2 sensor 1. I'm going to try swapping the O2s with each other to see if it changes sides, but I doubt one is bad since they are brand new. Going to do a vacuum test and maybe a compression test on Monday. What else should I do?
W
W
