Hey there I am stumped

I have a misfire on #6 cyl.

I have tested the fuel pressure, I am good there, I have replaced the plugs, wires and coil packs.

I have pulled the heads, replaced lifters, push rods, checked liners, replaced heads with good reconditioned units.

I have replaced all injectors

MAF Sensor Changed out

I changed out the catalytic y pipe for new

I changed out the o2 sensors (even though I have some bad readings there, need to clean up connections)

I have swapped out the ECU

I have changed the Battery

The misfire does not show on the nanocom while idleing, but give it some gas, it starts counting steadily on #6 only

When I take her out on the road you can feel that misfire



Error codes

P1300 Cat damaging Misfire

P1000 Cyl 6 Drive Cycle C

P0134 Lambda Sensor Upstream Bank 1 drive cycle C

P0300 Emissions relevant Misfire

P0306 Cylinder 6 drive cycle C

P0141 O2 Sensor Heater Downstream, Catalyst Bank 1 Drive cycle C

P0161 Lambda Sensor Heater Downstream, Catalyst Bank 2 drive cycle C

The answer may be right in front of me, but could use some GURU knowledge on this. Thanks

 

Have you done a compression test on that cylinder? It's possible your rings are worn out.

 

all cylinders within 15% of pressure

 

Well, the only other thing I can think of is a worn cam lobe. You've replaced everything else.

 

How can I check the timing of the spark, I believe is sparks off stroke also and want to make sure it is getting both sparks

 

Have you looked inside 6 with a boroscope? You could have a small amount of coolant seeping in from behind the liner, it would be apparent around the head gasket area. You would also see a buildup on the spark plug electrode as it gets burnt off which is what leads to the small misfires.

Or else yes, I've had the worn cam lobe before too. But that was caused by a bad oil pump. If you haven't had a bad oil pump and or low oil pressure issues then this is probably not the case.

 

I completely remove the heads just to double-check and make sure I didn't have any coolant leakage or slipped liners. Everything checked out okay I put on some reconditioned heads with redone exhaust valves just in case and new head gaskets all the way through

 

Have you tried a leak down test on that cylinder? I just had a random #6 misfire. Pulled all the plugs and pressurized #6 to find the Air leaking out of #8.

 

"I completely remove the heads just to double-check and make sure I didn't have any coolant leakage or slipped liners"

The only way to check for coolant leakage with the heads off is to pressure test the block, usually at operating temps. You did that?

Again I would suggest what Abran said, or pulling the #6 plug and looking inside while the engine is still warm and the coolant system is still under pressure... If you see any bubbles at all then you have found a coolant leak... The kind that would lead to a misfire. I only say this because you seem to have done all the other troubleshooting.