rattling from engine

[redpenguin]

this problem has baffled me and everyone i've asked for the longest while:

i have a '92 RM w/ the TBI v8. 85,000 mi. a rattling noise (sounds like a bunch of ping pong balls) comes from the engine around 1500-1800 RPM when the engine is warm. it does not have any particular rhythm, and goes away after about 1800 RPM. from a stop, i sometimes hear one louder ping pong ball noise, and then it stops until about 1500 RPM when it reemerges. for a while, i thought it was pinging, and tried a different grade of gas but it can't be pinging, because it does not occur under heavy load. and it does not make the noise when the engine is cold up until about 180 degrees.

does anyone have any idea what this could be?

[MagicRat]

Pinging does not always happen under heavy loads, partcularly with an EFI car with a knock sensor. A malfunctioning EGR valve may be contributing to the problem.
I assume the higher grade of gas did not help........

It may be a loose/worn timing chain.

It might be a worn oil pump is not producing adequate oil pressure. The noise may be from lifters that are not pumping up or from loose bearings.
Try installing an external oil pressure gauge. See what the hot idle pressure is. IMO anything below 20 lbs is a bit low.

You could try changing the oil with a thicker grade, too. This would help compensate for wear.

The engine may just be worn, with excessive piston clearance or loose/worn piston pins.

Finally, don't forget exteral problems. Sometimes loose torque converter bolts or a cracked flexplate can mimic engine problem sounds.

[Loekee75]

Do you possibly have any stored trouble codes? Not all codes set the ENGINE light