Ok i have a huge problem i have a bad misfire on Cylinder # 5.

First I'd like to give a little back ground on the car. I just bought this car a month ago. The Car has 15,000 miles on it, Motor was Swaped by the dealer to and LS6 at 11,500, because of a bad Oil pump on the Ls1. Shortly after that the first owner Starting modding. The car now has Patriot Stage 2 5.3L heads, G5x2 cam, tuning by TEA and normal bolt ons. The car has ran fine untill last week, when i started getting a slight misfire at 4500rpm and greater, but was fine at all other rpms. Now a few days later i can bearly drive the car its missing so bad at all rpms.

Now to the things i've done to try to fix problem. I first checked the wires, changed the coil, changed all the spark plugs changed that injector, and all the wiring between the coils on that bank. I still got nothing, drove the car for a few days and last night i dug into it more when the misfire got real bad. I pulled the valve cover checked the valve springs, they looked ok to me no cracks, checked the rockers, and pushed on the push rod and lifter to make sure they weren't collapsed. Then i did a compression check on that cylinder and got a little more than 150 psi or i think 10.2 or so KPA. I have no idea what to do anymore.

Also i have no idea if this is related but about everyweek i go through O2 sensors first bank 1 then bank 2. It get an o2 insufficient switching code. System ran lean.

Please can someone help me figure this out. Maybe there is something im missing.

Thanks
Justin

 

Lets try this one in the Diagnostic section.

 

Does the misfire move with the spark plug or wire? Have you tried wetting down the ignition to see if anything is arcing? Is their any vibrations such as the driveshaft not balanced? Is your coil packs ground good?

Also remember if more than one cylinder is misfiring the misfire current counters may only increment for only one cylinder. If cylinder 8 and 1 are misfiring yet only cylinder 8 increments on the misfire counters.

 

I had a mis-fire above 4500 that I found to be a bad coil. I used EFIlive to tell me which cylinder it was. It said it was cylinder #4 but it ended up being cylinder #3 that was really missing. It read one cylinder off in the firing order, this really confused the diagnostic process. Just make sure that the cylinder that you think is missing is really the correct one.

 

monodax
The miss doesnt move with the wire i bought a whole new set of wires just to be sure. There are no vibrations that i know of, i assume my coils are grounded enough. I dont have all my coil rack to valve cover bolts in but i never have since i owned the car. I have not tried wetting down the ignition to see if anything is arcing. On autotap i have each cylinder misfire up seperatly 1-8. They are all missing a little at idle because of the cam, and cylinder 5 is horrible and cylinder 7 is a little worse than the rest, but goes away after idle.

2001WS6Vert
I assume the miss is on cylinder 5, i have changed all the plugs and all the wires on the whole motor and i replaced every coil on that bank with new coils and new coil to coil wires. How am i to be sure its cylinder 5, i only have autotap. I noticed cylinder 7 is missing a little more than the rest to. But like i said i have changed everything so far on that bank.

Thanks for the help guys.

 

Did you check the pushrod itself?A friend of mine recently experienced the same thing,pulled his hair out for a week trying one thing after the other.He also bought the car and had a miss almost immediately,turns out the push rod was broken and starting to mushroom.He pulled the rod out used a pen magnet (1.78 Autozone)to retrieve the pieces,dropped in a hardened rod and it's good to go.

 

If your Autotap is mis-reading like mine was the true mis-firing cylinder would be #4 (other bank) which is the next one in the firing order. I was really tearing my hair out because of the mis-information, just one more thing to check.