Help guys, I've just had all the engine mods in my sig done and the car runs like crap. Idles good, but will only rev to 5500rpm before what sounds like a mechanical missfire, not electrical, when cruising in any gear (M6).It wont rev higher. On a light throttle the car's driveline is shaken violently back and forth. After the tuners mechanic removed the LS6 inlet he told me the underside was extremely dirty as if a exh valve was staying open to long,also maybe causing a popping sound they could hear. I have found out the mechanic that did the mods installed the cam dot-dot but did not dial it in as he had no cam card, could this be the problem. I am gutted this has happened.
sorry about long post.

 

Not likely to be caused by not degreeing the cam in. Dot to dot should be plenty accurate enough to get you running well. I would look for the cause of your misfire. Start with the easy stuff like plugs and wires and coils, then move on to a compression test to make sure the valves are sealing. You may also want to check for any leaks in your intake that may be throwing yoru tuning off enough to cause such a gross missfire. That should be enough to get you started. Good luck!

 

A couple of things may be the problem. One of your dual valve springs may have one of the coils broken causing a float at higher rpm's. Not good. An LS6 intake manifold seals to the heads and I don't see how an exhaust valve staying open could cause the underside to get dirty, UNLESS it isn't sealing, which could definitely cause your problem. If the heads have been milled or installed on thinner than stock gaskets that cam could have caused a valve to kiss a piston and bent a valve. You did not say that this was happenening from the first start of the engine after the work or if it happened after a while.
My best guess is you have had piston to valve contact and either have bent a valve. What has caused this could be a broken valve spring and float, an improperly phased cam, or heads milled too much for that cam and piston to valve clearance not checked.
Just my $.02. I'm hope it's just a badly sealed intake manifold.

 

Heads are standed, While running on the dyno we found no electrical missfire, the car was like this from the moment i got it back from the shop,took it back and they tried to blame the cam,and had another go at fixing with no luck, so it is now at another shop who are more upto date with the LS1, but at the moment it has them stumped. Car was running perfect before these mods, the motor has has only 30,000mls from new.

 

by any chance can a low oil presure cause this, the pressure hasn't been checked yet,what should it be at. I did not replace or port the original oil pump. With the dual valve spr and big cam is this a possible cause.

 

do a leak down test and see if you have bent valves.Then pull down the front of the engine and make sure the cam is installed right.

 

Thanks, will get the shop who have the car to check, as the car is 200mls away.