Hi, I hope someone can add some insight. Our 2000 suburban (5.3l, 218kmiles) started idling rough last week. I plugged in the diagnostic tool and it indicated cylinder 7 was misfiring. So I changed the spark plug. Same issue. Switched some wires around, no change. Switched coils, no change. Switched injectors, still the same. What else is this likely to be? I'm not ready to throw in the towel yet. Thanks for the help!

 

have you checked compression ?

 

Not yet. I didn't know what was involved with that. Now that I have seen a video on testing the compression I'll give that a check.

 

I have now checked compression on 3 cylinders. #3 was 145, #5 was 152, #7 was 15. Are there options aside from a new engine?

 

Pull the valve cover and check for a broken valve spring on #7.

May need to pull the head and check the valves on #7. Could be a burnt valve, chipped valve, bad valve seat, etc.

 

With such low pressure I suspect it should be something like a broken valve spring. Do report back with what you find once the valve cover is off...
Short of a hole in the piston, its not an unreasonable repair..

 

I forgot to mention that if you do find a broken valve spring, you will not have to remove the head to replace it. Let us know what you find and we can detail how you can do that.

 

Ok, so the forward of the two valves associated with cylinder 7 has "rod" (opposite the spring) that is broken at the connection so that the piece that connects the spring to the rod (is that the lifter?) can move freely. Now what?

 

You have two choices when you have a repair to make:
1) Do it yourself
2) Take it to a mechanic

If you're going to take on a repair yourself, make sure you have enough know-how to do the job, make the fix, and not make it any worse. If you don't even know the proper terminology, it's likely that you should choose option 2.

You can't do a DIY job by getting advice over the internet. I still can't tell from your description if you have a broken rocker arm, broken pushrod or a bad valve spring.

Here's a video that shows the parts of the valve train and how to remove/replace:

 

It is the connection at the rocker arm and pushrod that failed.