Ok my 4.0 in my 92 makes a Diesel sound. im looking to see if anyone has FIXED or FOUND what makes the sound. Key things here are,Its not flexplate bolts, its coming from the motor and doesn't ALWAYS make the noise. It will do it hot or cold. And when it does it ,if i bring the rpms up a bit it goes away. motor has excellent oil pressure hot and cold. Has a ton of power,burns no oil and it very well kept up with. I run an elec fan, so theres no fan clutch, fan pulley, theres a new idler, alt, p/s pump, and water pump is in good shape. Noise is starting to bug me. I had the oil pan off not to long ago to do the RMS and everything was super clean (no broken piston skirt) not a sludge filled motor.

 

Btw I had rotella 15-40 in it with a bosch filter, it made the noise so i went to 10-30 with a stp, still the same.

 

Mine sounded like a diesel too. In my experience, the thicker the oil I put in, seemed to make it worse. So I put a 5w30 synthetic in it, no more noise..

 

hmmm anyone else?

 

mine did that. both actually. its probably valvetrain. it could also be piston slap... didnt hurt.

find out if its top end or bottom end first.