My 92 4-runner v6 3.0 runs smooth at start up but it reaches normal running temp there is a pinging noise at 3000 rpm or greater. Changing fuel doesn't seem to change it. Does anyone have any ideas what might be causing the problem?

 

When you say "3000 RPM or greater" you did not mention if that was under load (driving) or at idle. Which is it?

 

The pinging can be heard even when stopped and just revving .... It also occurs during driving but doesn't seem to matter if climbing a hill or on a flat section

 

I would look for something loose on the rotating assembly then. The idler pulley is of particular interest here. Shut the motor down and check for play in everything you can, such as the PS pump pulley, AC compressor pulley, etc.

This doesn't sound like detonation to me since it is happening while sitting there and revving it too (rarely does that happen unless your timing is completely whacked out).

 

Check fuel injection pressure at the rail. If its low, you are running lean, which will ping. Then the question is, 'why is the pressure low'? Not many things to go wrong here: Fuel pump, regulator, filter.

 

I'm very impressed unhappy.... diagnostic skills at its finest. Ever thought about working as a mechanic?

 

I take shadetree mechanicing one step farther and work entirely in the dark.