S-10 knockin......but not rockin!

[StevanSimmons]

My 4.3 is making a metallic sound near the rear cyclinder on the drivers side. It doesn't do it untill the engine is reved a little bit. I'm parkin it till I can get it identify and fix the problem. What are the things that would cause this noise and which one is most likely?

[curtis73]

Try to identify the noise as a tick, clunk, scrape, etc.

It is one of several things. 1) Injector cycling noise if its an MFI (not carb or TBI), 2) valve tick, or 3) Rod knock.

An injector noise will sound like a subtle click, kinda muffled like someone tapping gently on the floorboard while your in the car. From outside under the hood it sounds very similar, but a little more treble. Not a full-on tick or snap, but a muffled click. Another way to tell if its the injector is by listening very carefully (many ears can't hear this but I'm a musician If you hit the accelerator, a ticking injector will speed up before the RPMs of the engine. This is how it simulates the acclerator pump for enrichment.

A valve tick will sound a little more metallic. Picture the pushrod snapping against the rocker arm and thats just what it sounds like. It has a little more treble to it and a slight clack to it. Put a stick or screwdriver handle against the soft tab infront of your ear closing off the canal. Put the other end on the valve cover and move around. You can usually identify the culprit valve where the noise is loudest. If you don't find it, its most likely not a valve

A rod knock or spun bearing is a clunk. It sounds like somone hitting the bottom of the block with a hammer.

Injector noise = no problems. They all do it
Valve tick = fix it soon, may cause catastrophic failure from oil pressure drop but unlikely unless something is completely broken. Probably just a collapsed lifter.
Rod knock = bad news. Tear it down, lots of machine work, bottom end rebuild.

Curtis