cylinder not firing?

[Guest Death69]

well i posted this in the L series forums but got to thinkin that not everyone looks at those. so im posting my question here also. at start up, the car sound fine for 3 seconds, then it sounds like it dies then suddenly starts back up. it does this 3-4 times depending on the day and then goes into normal idle, but it still doesnt seem right. i was told that one of my cylinders wasnt firing properly, but am unsure. i will have a sound clip up next weekend. there is a crack in the exhaust (maybe) which i will be fixing ASAP or atleast before i start the car back up again. i was told the crack could lead to a burned valve but am unsure. i dont want to spend lots of money correcting the problem and have it be something simple. the cars a inline 6 78 280z. any help is grealty appreciated.

[endurorider]

Lets start with a compression check. then put a vaccum gauge on a vaccum port on the intake. We want to pull all the plugs and crank it 4 times then take the reading. We want to see the compression even within 15 psi. if compression is much lower on a cylinder the drop a little oil and do a wet test. see if it comes up. If ok put a vaccum gauge on port vaccum with it idle and see if it steady. if it fluctuates real fast, its a valve. How is it after warms up? If its on cold start , could be a cold start injector not firing or idle speed controller.

[VinhZXT]

When it's tumbling (feel like running on 3 cylinders) shut the car off and inspect your spark plugs. If any of them are wet then that cylinder is not firing. Replace them all with new spark plugs and try start the car again. You will be amaze some spark plugs will give you sparks when you test them out side but when inside the cylinder they won't fire. GL.