Cylinder 5 misfire mystery

[1994alexb]

I'm having a weird issue where cylinder 5 is misfiring. It happened after a transmission line blew off and filled the engine bay with transmission fluid. It didn't happen at first, but a few days later the stabilitrak light came on and went away and after that the misfire only got worse and the stabilitrak will come on intermittently like the misfire. The misfire isnt as bad when cold but gets bad when hot. The stabilitrak message usually comes on when it gets bad and makes the 1-2 shift harsh, so I'll usually start in second and once I get moving it usually dissapears. It also mostly happens at idle or no load, but not at high rpm's. Mostly under 3k rpm and light to no load. I changed the maf, the throttle body, plugs/wires/coil for cylinder 5, tightened all the intake bolts, changed the fuel injector, ran some fuel system cleaner since the filter is in the tank, but all these things did not work. Tomorrow I'm going to try a napa block tester to see if there's any combustion gases in the cooling system. Maybe some ATF got onto the valves and isn't sealing now? I'm scratching my head with this one. Any ideas?

 

07' Sierra NNBS 5.3 LH6/4L65E

Edited July 26, 2020 by bishop94z

[davester]

Perhaps check/clean the wiring to the injector and/or coil for that cylinder?  Or perhaps the knock sensor and/or wiring (not sure where it is on your engine, if under the intake manifold they are probably fine unless a bunch of fluid got under there as well.

Edited July 26, 2020 by davester

[1994alexb]

On 7/26/2020 at 3:22 AM, davester said:

Perhaps check/clean the wiring to the injector and/or coil for that cylinder?  Or perhaps the knock sensor and/or wiring (not sure where it is on your engine, if under the intake manifold they are probably fine unless a bunch of fluid got under there as well.

For sure, I’ll give that a shot. It’s the GEN IV setup. Haven’t gotten any knock sensor codes but I’ll replace them anyway. I’m hoping it’s not a wipes cam lobe but I would think it’d cause a constant misfire instead of an intermittent one.