1994 Mazda Navajo motor noise

[snow540]

I picked up this navajo two years ago as a daily driver when I first got it it would make a pinging noise at around 65 mph in 5th gear and the rpms around 1700-2000. It was not that bad and I just kinda learned to live with it as it does not see the interstate much. This past winter it seemed to be making it a little worse at all speeds. I tried fuel injector cleaner, higher grade gas, even ethanal free gas. No difference. I picked up car that gets great gas mileage, so it did not get driven a lot this summer, 30-50 miles a week. All this past summer the times I was driving it it seemed to be getting worse, now I have parked it until I can figure out the problem as it has gotten so bad.
It does not sound like any rod noise or lower internal problem, at idial it does not have any valve noise, even reved up it sounds fine. When the motor is cold it is not that bad, but as soon as you hit operating temp and put any load on the motor it makes a horrible pinging noise. It will not climb any kind of small hill without it sounding like the motor trying to come out of the hood. There is no bucking or surging of the truck, it runs smooth just sounds terrible.
First I have thought about the ignition timing being off? The EGR not functioning properly? Even one of the temp sensors being faulty? Any ideas of where to start would be great. Thanks.
It is a 1994 with 167k, 4.0, 5-speed, 4x4.

 

[TexCaliBII]

If your sure its not a rod then most likely it may be a buildup of carbon on the valves and piston tops causing pre-detonation in the cylinders. That can make a car sound like its dragging a chain behind it. And it definitely gets worse the hotter the engine gets. The only real way to check is pulling the heads, or looking through the spark plug hole you might see a large carbon buildup on the piston. If there is then you can bet the valves are gunked up too. An old school way to clear it up some was dribbling some auto tranny fluid into the carb but as these are fuel injected, well. Seafoam put into the induction system via a vacuum hose can do wonders too. Hope you get it figured out!