It's unfortunate that a loose pin sounds pretty much the same as a defunct rod bearing, but with a little patience you should be able to determine what's at fault.
First, check idle oil pressure even if you have to screw in a mechanical gauge. If it's low, you can bias your decision toward bearings.
Next, listen with your stethoscope. A rod bearing makes more noise at the oil pan than elsewhere, and a wrist pin more racket up on the water jacket. Hold RPMs at 2500, **** the throttle open and let it snap closed. This will accentuate rod knock, whereas pin noise won't change very much.
Now's the time to starting shorting out cylinders. A bad pin will quiet down, but a rod knock will double its cadence.
Finally, you can pull the pan for a visual inspection. If the bearings are good, you know you've got a pin problem.
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If you can make the knocking stop by disabling that cylinder, the problem will be in the piston and wristpin. The fit of the wristpin to the piston is too loose, causing the knocking. The fix for this condition is to disassemble the engine and replace the particular cylinder piston and wristpin.
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3) Get the fuel pressure checked.
If its less then its quite possible that fuel pump needs to be replaced and
fuel filter is got clogged.
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