lsxTAlemy

iTrader: (2)

guys i have an ls2 z28 built for nitrous built by a supposedly reputable local shop. has forged rods and pistons on stock crank motor was balanced . vibration comes in at 2k leaves and come back at 4k then leaves. full throttle i wont do it. only does this when u hold the rmp on at the rpm. the shop guy told me to double check the crank pulley. i changed for a new one.. told me to tune it. i tuned the car now hes telling me to check for miss fire or flex plate. changed out plugs, wires and swapped coils. separated the trans for the motor and the vibration still there, but less noticeable. with the trans on it amplifies. i will changed the flex plate tonight and hope this nightmare is over. anything else u guys think i should check...

the car performs well, runs real strong. but the vibration has me worried... motor is supposed to hold well over a 300 with out braking a sweat...

thanks in advance

homemade87

This is just a thought . You may have a cylinder that is not firing . Under certain conditions it will give a weird vibration also seems to run ok except for vibration . ecm may not be picking it up . Could be a injector stuck . Easy test is to find a infrared gun and check the header tubes for heat difference . One will be cool .

Worth a check since you are chasing your tail.

lsxTAlemy

iTrader: (2)

thanks. any other thoughts???

lsxTAlemy

iTrader: (2)

swapped out flex plate and another set of coils and nothing! im going to check the header temps and see whats going on..

really not looking forward to ripping this motor back out and sending back...

homemade87

Hopefully is just a stopped injector . The ls injectors are really bad to stick when they sit around a while . You see people on here quite a bit trying to figure it out and find several stuck injectors .

If not a injector it will lead you to the problem area if you do have a cool cylinder .

A.R. Shale Targa

iTrader: (2)

Assuming the rebalance was properly done, rpm specific vibrations point to a cracked crankshaft.

lsxTAlemy

iTrader: (2)

cyl #1 was a dead cyl we checked injectors and they were fine. changed the coils and we got heat back in cyl #1 vibration still there all cyl wroking.

well my brother went to the place where they had supposedly balanced and the guy said he doesn't remember the motor. he told us if he did balance it would have a number marked on the crank so we are going to drop the pan and see...