LT1-LT4 Modifications 1993-97 Gen II Small Block V8

first start up with headers, loud banging?

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Old Nov 19, 2011 | 11:59 AM
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Default first start up with headers, loud banging?

Well I got everything back on (finally) and when I started it up I heard a loud banging from underneath the car that would happen every few seconds, and when it happened, the engine seemed to loose rpms for a second and then come back up. What could this be?
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Old Nov 19, 2011 | 12:53 PM
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Anyone? I can't figure out what it is...
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Old Nov 19, 2011 | 01:07 PM
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Sounds like a clearance issue. Many times your heat shields are so close to the headers that you have to slightly bend them until you get the needed clearance. Also check your motor mounts, they could be getting weak and causing more movement along with the larger diameter exhaust which is causing the banging. Worth a try and it's free...
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Old Nov 19, 2011 | 01:14 PM
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headers hitting bottom of the car, computer thinking it's knock... BFH time.
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Old Nov 19, 2011 | 01:23 PM
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Alright those sound like what it could be. I tried driving it around and it got worse. Now it sounds like its backfiring...which I hear could be bad plugs or spark wires... Could an exhaust leak due to a part not being installed right also cause backfiring like that?
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Old Nov 19, 2011 | 01:25 PM
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Vtec?
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Old Nov 19, 2011 | 01:35 PM
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First burnt plug wire on new headers, and shitty mounts allowing movement and causing headers to bang on something plus causing knock retard
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Old Nov 19, 2011 | 02:08 PM
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like stated, normally it will be a Kmember or transmission mount/crossbrace. Also like stated its thinking its knock (must be damn loud!)

Car sounding like its backfiring doesnt seem related. Like stated...burnt plug wire, or some plug wires got crossed?

I would start it up, and get under it looking for the areas the loud bangs are comming from. You may need to reposition the y pipe. Would also double check that the plug wires arnt crossed and look for a burned one.
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Old Nov 19, 2011 | 02:49 PM
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Alright, I'll check the wires and plugs this week as well as where its banging. The banging went away for awhile, but then came back, so its confusing..
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Old Nov 19, 2011 | 09:09 PM
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Alright I"m pretty sure the banging is actually a backfire. I'm thinking the backfire could be causing the exhaust to hit something when it happens. I'm going to check my wires and plugs and hope that's the problem. It sounds like a shotgun going off actually. And it doesn't happen consistently really. It will backfire and then a few seconds later it will, then again, and then it might be like ten seconds before it doesn't again. So at times it seems like a sequence, but then it stops and then comes back. If the plugs and wires don't fix it I'll take a vid of it and post it and see what you guys think.
Sorry for the story there, just trying to describe it the best I could.
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Old Nov 19, 2011 | 09:20 PM
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To add to that, I've ruled out bad motor mounts for now (even though I will be replacing them) because I highly doubt that a sound this loud is caused by the headers hitting something. I am not getting an SES light either. Like I said, its like a shot gun going off which to me sounds like it would be a misfire, but I want to hear what you guys who have probably dealt with this before have to say.
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Old Nov 19, 2011 | 09:28 PM
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Make sure the plug wires are on the proper spark plugs. Sounds like the firing order is out of order.
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Old Nov 19, 2011 | 09:41 PM
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I can check that...but if that were the case wouldn't the backfire happen consistently? Not randomly?
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Old Nov 19, 2011 | 10:48 PM
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***UPDATE***

I found out that one of my spark plugs was very loose, I could move it with my fingers. Also it appears that the little silver part of the plugs that plug into the wire (the very end of it) are threaded and a few of them were loose. Could this really be an issue? What do you guys think? Bare with me here lol
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Old Nov 20, 2011 | 02:12 PM
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Alright, I tightened the spark plugs and what not, its still banging. Now I think that maybe it really is something loose that is just hitting the car somewhere. Now I just need to find out where its touching.
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Old Nov 20, 2011 | 02:24 PM
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its most likely where the y pipe connects to the header collector. there is a crossmember/floorpan there that sits very close to the exhaust.
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Old Nov 20, 2011 | 02:49 PM
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It just seems like even if it was hitting, that it would be so loud...I'll take a look under there and see what I find
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Old Nov 20, 2011 | 02:58 PM
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get a video of what you are describing maybe that could help...


also try doing it at a stop, in neutral if it doesnt bang when you stomp the gas and does when in gear... its probably a mount, trans or engine... or even exhaust hitting somewhere.
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