Ok wasn't sure which section to post this in and here is the reason. A few months ago I had my car out, it's a 91 Z28 with an LS1 swapped into it. I mis-shifted going from 4th to 5th and went into third doing about 130 mph with 4.10 gears in the rear, ouch. I only let the clutch out a little when I realized it and pushed it back in right away. This is the second time this has happened and the first time I guess I got lucky and the stock pushrods took the abuse. I replaced them with SLP chromoly pushrods and this time these were not bent as bad as the stock pushrods were. Started the car and now I have a random multiple misfire code of P0300 after I replaced the pushrods, replaced all 16. With my luck I'm thinking I have some messed up valves, anybody have some insight for me ? Thanks.

 

i thought multiple misfire had to do with your plugs, wires and/or coil packs???

 

I've been trying to research this since I fixed the car last night and have found a bunch of different things people are saying it could be from O2 sensors, injectors, fuel pumps in blazers causing this to a bunch of stuff. Since I manually over reved the motor and bent pushrods that is what is swaying me to bent valves or something along those lines. I've also heard it could be a bad crank position sensor but it threw the code right after I over reved the motor. Does anybody know the proper way to disconnect the battery so the computer relearns crank position ? I also have HP Tuners so does anyone know a way to maybe diagnose which specific cylinders are misfiring using HP Tuners ? I don't know how to use it that well and for that reason haven't really gotten involved with it any more then turning off DTC's for my rear O2's and changing fuel cut off, the easy stuff.

 

My vote is bent valves. Do a compression check, that will tell you very quickly.

 

your valves hit the pistons and are slightly bent.