Motor knocking

[Igenofish]

I have a 1988 GMC Sierra, 350 4x4
This just started. It runs and sounds fine just sitting there. Whenever I put pressure on the motor while driving, it starts knocking. I can rev it up in Park and it's fine. Only does it under pressure .
HELP!!!!!!!!!!

[maxwedge]

You need to have someone listen to this onsite, we can only guess from here.

[Igenofish]

Sorry, not sure what you mean?

[aleekat]

He means have a mechanic come to listen to it.

[Igenofish]

Cedar Bluff , Al. Looked everywhere here. No mechanics. Afraid to drive too far. Surely someone has an idea.

[Igenofish]

Don't get it. Happened all at once. Should be something simple. No signs at all.

[MikeCStig]

Usually if it were a rod or valvetrain knock, it would happen at idle, while revving the engine in park, and under a load. When it only happens under a load it's usually a spark knock, which is an ignition timing issue. Not as serious, but it does need to be fixed or it can lead to more serious issues.

[Igenofish]

Had timing checked today. It's right on. Back to the drawing board.

[aleekat]

only in drive. then driveshaft, gear box, tranny...etc..

[Igenofish]

Will lok into that. It's just that it definately sounds like it's coming from the engine. Almost as if it were bad gas. Tried to remedy that also. I'm just lost here.

[Stealthee]

You need to check your ingition system, from your plugs to wires, to cap to rotor. I bet you'll find your issue there,.

[Igenofish]

I have replaced plugs rotor button and Cap already. Wires look good in the dark, but haven't replaced them. Truck runs like a champ until it is put under pressure. Driving only. In park, sounds fantastic.