Okay, I installed an LS6 intake on my car on saturday. After the initial startup it started misfiring. (The SES light was flashing, which by the manual means a misfire). The light was flashing but audibly everything sounded fine. Took it for a drive and it was kinda slugish, and upon acceleration I could hear an air puffing sound. That's the best I can describe it, it was like air popping with the cylinder firing. During the drive the SES would flash for a while and then would stop for a while, then start again, then stop, etc. Brought it back, and we pressed down on the fuel rails again to see if the injectors weren't seated fully, and also pressed in all the sensors to make sure they were seating. Took it back out for a drive, no problem at all. Ran great, no misfiring, no air puffing sound.

Fast forward to tonight. Car probably has ~70 miles on it since then, and I've been WOT close to 10 times with no problems. I let my uncle drive the car for a bit and he didn't take it past 3500 any, but after I drove it again after the air puffing sound is back and it's misfiring again.
Anyone with thoughts on what the problem could actually be? I don't know what would be a problem once, and then go away for a few days, and then just come back. Only thing I could think was that we busted an injector or something, but that would be a constant problem, wouldn't it?

Oh yeah, during the install there was a point that one of the injectors put out some fuel. The guy helping me got some on his fingers as we were pulling the injectors out of the intake and we were concerned we busted it. But it didn't happen again after that. We didn't know if you actually put pressure on a part of the injector if it would let out fuel.
I'll probably go get it scanned tomorrow to see if anything is showing up. I already have the SES from !AIR, !EGR, and rear O2 removal, so I'm not sure if I'm throwing a new code now or not. Any help would be appreciated.

 

Everything plugged in behind the intake..camshaft sensor etc...? Check plug wires...sounds like a plug wire may have fallen off or be loose, probably from the coil end. Are the AIR tubes leaking..missing gaskets..? All you did was change the intake manifold?
When you pushed down on the injectors the problem went away for awhile? If so, I'd pull them back out and look for missing or damaged o-rings.

 

Everything is plugged in, that got checked 10 times before it got started. AIR has been removed, I just put on headers before this. All I did before this problem was the intake. I'm starting to wonder about the o-ring of one of the injectors also, maybe one is damaged and will seal itself for a while but then it works its way loose. The problem went away again and has been away for like 10 miles, I'm gonna recheck all the connections again. If it comes back again I'll probably pull the fuel rail and check for missing/damaged o-rings.

 

make sure you have the brake booster in correctly, the sensor and the little vaccum line in the back all on right. Reseat the injectors. Press on the back, then on the fronts to seat them well. Do it on both sides. then make sure the bolts are all tightened down nice and tight. make sure the plug wires are on the coil packs nice and snug. you should feel a click. also check the boot on the plugs. If you have the egr still in, then check the oring and make sure its not in there crooked. One thing i didnt check on mine before i installed it was to see if there were gaskets in the manifold to begin with-----major vaccum leak If you have to pull it again to make sure, do it. Its only about an hours work. Its so easy. Just be mindful of the oil pressure sending unit.
Also, make sure you torque the manifold bolts down correctly and in 2-3 passes. ls1howto.com has the write up incase you didnt know Hope this helps.
Nino

 

Yes..good point on the intake gaskets. Did you use new gaskets or reuse the old ones? Always use new. Torque sequence and correct ft lbs are also important.

 

The new intake came with new gaskets already seated into the ports, so that was cake.
Question about the little vacuum line in the back though. Is it one peice that attaches onto teh manifold, and is there then another hose that seats into that first peice as well? The first peice has a "T" connection at the end, part of it I put on the manifold, and then the other hose I plugged into the other side of the "T". Was that right?

 

Yeah that should be right. Mine is a 98 so it doesn't have that but I've worked on several newer cars that had that type connection. It's just a vaccum access, so it shouldn't matter as long as everything is plugged in.
Always put a little engine oil on the fuel injector o-rings before installing...

 

Didn't do the oil thing.