Cylinder-1 Misfire: advice needed

[Salonika]

While you're in there I would compression test the engine, just for fun.
Indeed

Planned a cylinder leak down test (not a compression test).

Any thoughts on why you would pick one over the other

 

[MontySquareo]

Actually I think a leak down test is more useful than the compression test. I just said compression test because many people have the tools to do that

 

[Salonika]

Update: injectors were sent out for diagnostics and they all passed with clean bill of health. Still need to complete compression testing. After that, spark tests, then look at injector wiring. Nothing jumping out at me so far.

 

[Salonika]

anyone ever see a manifold vacuum leak cause a misfire in only one cylinder?

 

[Michael Brown]

It could be a possibility. Bad gasket or leaking hose letting most of the air into 1 cylinder might happen at the front of the manifold.

 

[Salonika]

UPDATE: It was the manifold upper plenum gasket. The evidence had been staring me in the face for a while, carbon buildup on the outside of the manifold right around the seal. I saw it……ignored it. For a while it was visible but did not cause me any problems. Maybe a manifold bolt came loose. The carbon traces were right next to the #1 cylinder intake pathway so there is my misfire on cylinder-1. It isn’t back together yet but will be soon then I will know for sure.

 

[normal_dave]

UPDATE: It was the manifold upper plenum gasket. The evidence had been staring me in the face for a while, carbon buildup on the outside of the manifold right around the seal. I saw it……ignored it. For a while it was visible but did not cause me any problems. Maybe a manifold bolt came loose. The carbon traces were right next to the #1 cylinder intake pathway so there is my misfire on cylinder-1. It isn’t back together yet but will be soon then I will know for sure.

"All my misfires have been plug wires..." (sung to the tune of exes from Texas). Well except for that one time that I had a dead coil. Sounds like you nailed it but don't forget to double check the obvious items while you are in there.

 

[Salonika]

All back together and running fine now. I did put in new plugs and wires while I was in there, but the old ones looked and tested fine so I never suspected them. Turns out it was simply a gasket leak on the upper plenum. I’ll never know for sure, but you aren’t supposed to have carbon buildup in that area and I had a lot of it. Had I been thinking about it I could have checked the torque on all the manifold bolts before doing any other troubleshooting. That would have likely fixed it. Oh well. Lesson learned. This also means I probably could have fixed it on the road with a 12mm socket in about 10 minutes.