1999 5.7 mercruiser (Fuel injected) backfiring issue

[BroadHopper]

Tuliped valves on 350 GMC engines are quite common! I and buddies of mine had the problem on fairly new 350 Mercruiser engines. If the engine is within the warrantee period, Mercruiser will replace free of charge. After the warrantee service, depending on who you talk to at Mercury, they may or may not replace the valves. In my case, my insurance company paid for the replacement. Check your insurance company.

My uncle has a fleet of GMC trucks with the 350. I remember him telling me it was a pain dealing with GMC regarding tulipped valves.

Originally Posted by dippasan

I performed a compression test on the engine
this past Saturday.
7 cylinders showed 175 psi but #4 cylinder has 45 psi.

In talking to my mechanic, in the 90's for some reason, it was a common problem to "tulip" a valve. Probably an intake valve hence the backfiring through the throttle body. I removed the valve cover and ran the motor and saw nothing out of the ordinary with the spring, push rod or rocker (as you might expect because the problem is on the combustion chamber side).

So it looks like I have a valve job in my immediate future. I'm just a little stumped. I've worked on cars my whole life and I've never had a valve fail on a motor. Especially a Chevy 350 which are typically bullet proof. These motors have 360 hours and run as sweetly as can be with no sign or indication that a valve would fail. Strange!