Did a bad injector blow my valve ?

[Sveedy]

After taking some time off from turning wrenches and just enjoying driving, I am starting on the head job for Sveedy.
As I'm wondering what caused a valve failure after only 30k miles, my first thought was a bad valve stem seal. But I happened to notice this pattern on the intake side, which is making me think that the cause was a injector that was putting out way too much fuel.
Am I barking up the right tree ?

Intake side

The difference is much more apparent in person. It almost looks like its been cleaned with cleaner. Hard to see any spray pattern on that cylinder.

[scot850]

Interesting question! Hard to tell and sorry if I missed your mentioning it. What cylinder failed? Was it #2?

Looking at your pictures, it looks like the intake on the failed valve is definitely clean which could mean it has had too much fuel in there cleaning the intake of carbon. It may be worth considering taking all the injectors and have them serviced to see if any of them are sticking open and dripping into the intake. If they have never been cleaned it is probably a good idea to have that done anyway.

Initially I thought from the description it might have been a leaking cylinder head gasket which I'm sure you know steam cleans the piston(s) where the coolant leaks into, but I'd expect the valves to be cleaned too.

If I recall the older cars like the 850's used to have a extra seal ring on the outside of the injectors. I have found cars where some or all are missing. Not quite sure what the purpose was for in the first place.

To me the main causes of valve damage are still:

1) Engine or cylinder running too lean
2) Leaking valve seals allowing oil/carbon build up on the valve seat and stem causing the valve to overheat.

Disappointing that the engine failed at such a low mileage after all your previous work.

What gas do you run the car on? Regular or Premium (87 or 91/93). I'm still a believer that running one of the P80 turbo engines on 87, especially on highways or steady higher speeds, causes overheating. It is also strange that the majority I have heard with the burnt valves is cylinders # 2,3,4? Strange.

Did you use new valves when you did the rebuild or did you re-use the originals?

Neil.