Anybody wanny help me diagnose engine noise?

[Johnstra]

I'm trying to pin down a noise on my 92 V6 Toyota Pickup. Here's what I have. Basically my little gasser sounds like a little diesel at idle. Here's a better description...



Steady knock/tap in sych with engine RPM - most noticeable when engine is warm and at lower RPM (<1200). Listening closely with an improvised stethascope, my ear wants to locate the sound at a lifter or valve. I can't pick the sound up very well at all from the bottom end. With my scope on a cylinder head bolt or valve cover bolt or on the exhaust manifold I pick it up very well. Sounds metallic so I'm pretty sure its not an injector.



Possibilities:

lifter

exhaust leak (except that it sounds metallic to me)

piston slap

rod knock



I'm hoping its not piston slap or rod knock as I plan to do some work on the top end and I don't really want to have to pull the engine. If it were bottom end, I would think the sound would be most noticeable at higher RPM (wouldn't it?).



Ideas?



Thanks,

-john

 

[JLEONARD]

Try running it and listening with the valve cover off... . I would think a lifter/top end noise would be louder then. That might help you pinpoint it.

Jay

 

[mcoleman]

If the noise is going away as you give it more gas it is most likely a lifter. More gas equals more rpm which equals more oil pressure that would quiet a lifter that is bleeding down at idle. You might also run the valves assuming it has an hydraulic valvetrain it could just be out of adjustment.

 

[Johnstra]

Mech. lifters w/ shims, but I'm still going to measure/adjust them.

 

[SGibson]

try pulling a plug wire one at a time, start the motor when its sat for awhile and is stone cold and see if you can hear mains or rods rattle, does it do it on trailing throttle? there's a few driveway troubleshooting tricks.

 

[Johnstra]

I'll try pulling plugs tomorrow, SGibson, to see how it affects the sound. It does not do it on trailing throttle and it doesn't do it at higher RPM either, which is why I'm leaning away from thinking its bottom end.



Another one I've heard is to squirt a little oil into each spark plug hole and fire it up and listen while it's cold. Piston slap will be greatly reduced by the oil.



Thanks!