teke184

this is kindda specific to the LS1 engine but i figure since i thinkk it may be valvetrain related not electrical/computer i would give it a whirl in here.

car will run PERFECT for weeks on end, but once you run it up past 4k rpms (give or take...not exactly sure) 10-15seconds later it starts misfiring on only 2 cylinders. number 5 and 7.

it will go from misfiring to smooth, in 10-15second intervals for a while then start running perfect again.
untill you runn the rpms up again

ideas:
weak valvespring allowing the lifters to pump up too much...not closing the valves?

bad lifters?

other possibility is fuel injectors

i'm gonna do a compression check soon, when i get some time, to see what is happening during the missfire.

thanks

slayer6x6

How do you know its not an ignition misfire?

kingman109

i too have similar problems although it only happens everynow and then

teke184

"How do you know its not an ignition misfire?"

well...i guess i don't...

but i've changed plugs, wires and coils to try to issolate it...to no avail

it started before i did all this...and still does it

RobertoZ28

Try switching the coil packs on the cylinders that are misfiring. If the problem follows, then you know it's the coil packs. Worth a shot.

kingman109

again i have same symptoms- changed plugs and about to change wires- ohh and the misfires are random cylinders....

heres codes ive been throwing

0151 -02 sensor low voltage
0300 - random multiple cylinder misfire
0400 - EGR malfunction - cleared and hasnt come back
1642 - not sure what it is
1657 - not sure what it is

slayer6x6

Are there letters before these codes? There should either be a B,C,P, or U.
B-Body
C-Chassis
P-Powertrain
U-Network
If you can find the letter, I would be able to look up the codes.

kingman109

ya allready looked em up - first is cause i bypassed skipshift - 2nd is my cooling fan rewiriing i did- so those arent problems-


gonna replace O2 Sensor and wires tomoroow- hopefully that fixes

teke184

"Try switching the coil packs on the cylinders that are misfiring. If the problem follows, then you know it's the coil packs. Worth a shot."


been there...done that...next

i guess what i'm looking for is a yes/no as to whether faulty springs or bad lifters could cause this. like maybe the spings are weak..alowiing the lifters to pump up higher than normal only under high rpm use.
or if the bad lifter would allow itself to pump up more...

i'm hoping a compression test shows this