OT: Question about Truck engine

Start by checking the timing (with a light), following the specified procedure, and also take a look at the 'puter with a scan tool, looking for codes pertaining the ESC (Electronic Spark Control).

If the knock sensor is defective or disconnected, the ESC won't be able to sense any spark knock, and the 'puter won't know to retard the timing as needed.

Sometimes, guys will pull the plug on the knock sensor on a worn engine, to keep the 'puter from "hearing" noise from a loose timing chain or piston slap, ind interpreting it as "spark knock", and therefore, retarding the timing.

Another thing that will cause detonation under load on these engines is a plugged or otherwise non-fuctional EGR system.

Unless you can determine it IS something simple like an exhaust leak, I guess the best advice would be to have a mechanic look at it, as continuing to drive it with it knocking will destroy the engine, if it's not too late already.

Another note... it the "check Engine Light" coming on, indicating trouble code(s) have been set? Does the check engine light come on when you turn the key towards "start", or has someone removed the bulb?

I always thought valvetrain noise got louder when the engine is placed under a load. Whenever I listen to an old gas tractor climbing a hill or pulling a heavier load, to me it always seems like the valvetrain gets louder or more pronounced and you hear more of a tapping noise instead of the humming of the motor. When they hit the clutch, it seems as though the tapping quiets down and then the humming is what you hear. Where do I have it wrong or what causes that perception?

Could be a lifter, could be flywheel too.

Even tho they have hydraulic lifters, they still need to be adjusted from time to time ('bout every 80K miles or so).

Allan

Are you sure it's a lifter making the noise?

You could take it to a couple shops and let them give you their free evaluation.

If it's a automatic, the flex plate on those can crack and make a knocking sound, but that's usually more of a knock as apposed to tapping sound.

If the exhaust manifolds are leaking, or cracked, they can make a tapping noise.

I am not sure it is a lifter making noise, the reason I posted was to see what people would come up with that would explain the symptoms. It does sound like it comes from around the valve cover/ head/ manifold area, but it is hard to tell. The noise isn't a knocking noise, it is similar to a person tap dancing under the hood. I'll have to check the exhaust gaskets and manifolds, but, darn , it seems that the engine is too quiet for that. You can barely even hear the engine noise over the tapping unless you really step on it. Thanks for the input.

Open the hood, have someone powerbrake it for you and then give it a listen.

Everything you've said so far really, really does sound like an exhaust leak. But, we just aren't there to hear your noise like you can. :>)

Allan