2009 4.6L running rough

[mcolvard]

I have a 2009 Genesis with the 4.6L, 125,000 miles. Suddenly started running very rough, stopped at a dealer and he recommended plugs and coils which we did, still running rough. Now he is thinking it could be fuel injectors or compression. Wanting me to throw a blank check his way until he finds the culprit. Wouldn't his machine tell him if it is compression? Is there a way to test the injectors? Perhaps a broken valve spring? Any help would be greatly appreciated.

Thanks in advance,
Mickey

 

[pmckechnie]

I hate it when a mechanic troubleshoots a problem by replacing parts.
The first thing to do is using an OBD scan tool find out what type of problem he is working on. For instance, it could be a cylinder misfire on one cylinder. Then check the things that could cause that problem like the spark plug. Usually can tell just by looking at it. While the plug is out, check the compression on that cylinder. If it has reasonable compression, that is not the problem. Check the coil or injector by swapping them with other cylinders. If the scan tool now indicates the problem has moved to a different cylinder, he will know what the problem is.
The above is just one example of how to troubleshoot a misfire problem.
Now, the real problem is that in a dealership, the mechanics don't troubleshoot, they are paid to replace parts. I would recommend you take the car to an independent shop that has a good reputation.

 

[mcolvard]

My buddies OBD shows random misfire on 6 & 8. He thinks we should swap plugs and coils to different cylinders to see if the misfires change. Do we need to swap the fuel injectors also? Can you clean the injectors if they are the culprit? Or, replace with new?

 

[Gunkk]

Hopefully it's only plugs, coils or injectors and not a valve spring or two. Swapping them around to see if the misfire follows is the easiest/cheapest way to diagnose. Let us know what you find out.

 

[mcolvard]

it's a valve spring

 

[mcolvard]

Are there any tutorials or youtube videos available on valve spring replacement?