Valve springs?

My  son's Fiero started misfiring the other day. We did the usual, plugs, cap, rotor, and set base timing. No improvement. Pulled all the plugs and did a compression test. The #5 cylinder was 20 psi. I had him shoot some oil in the cylinder and we retested. It actually got worse so I had him pull the valve cover to see if there was anything obvious.

Hmm, that might be a problem. 

So, I've never had a valve spring fail before. They don't appear to be bound under compression. He said it was turning about 3500-4000 rpm when it started running poorly.

What causes this? This engine is supposed to be fairly recently built with some sort of higher lift cam. Is this a case of cheap springs? Aftermarket cam? E36 M3 happens?

My plan is a set of new springs and keepers. What else should we be looking at while we are in it? Is there any reason to pull the head and look at the valve itself?

A borescope inspection doesn't show any damage to the top of the piston and the engine isn't supposed to be an interference engine. 

Thanks

You both are lucky it didn't drop a valve!

That being said, bad metallurgy on one spring is possible.   Maybe it had a nick or bad spot on it leading to the failure.

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My plan is a set of new springs and keepers. 

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This is the correct answer.  There is no way of knowing if the other springs are good.

A nick will do it.

I know LS1 springs are an upgrade for the 3100/3400, not sure if they fit the 2.8.

Thanks for the info.

He contacted a person today that is selling a wrecked Impala ss so LS4 may be the correct answer.

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Toyman! said:

Thanks for the info.

He contacted a person today that is selling a wrecked Impala ss so LS4 may be the correct answer.

 

Well, that would certainly fix it.   In the meantime it's a pretty quick fix to pressurize that cylinder and stick another spring on there.