Hey guys my 98 has 174k on it and Im starting to get the disel sound, coming from it. also i had to replace the sending unit but now the new one is going crazy yes i have oil in it. i was told everything from exhaust manifold, timming chain , to bearings . I just dont no where to start. Any suggestion ? I think I have a line on a engine from a 2000 expedition would that be a basic swap

 

I think 2000 is a PI engine and 98 is not, so not direct swap computer wise.
all would bolt up though.

 

The 98 has 2 sensors for the head temp/etc, where they changed in 99 to a single sensor. You will have to use the single design, and change your wiring a bit. All in all, this isn't that bad of a switch. There are numerous writeups on here about this upgraded swap.

Your OP sender might be good, but your oil pump screen might be restricted, causing the fluctuation of the gauge. I'd certainly put a mechanical oil pressure gauge on it to see what it really is doing. Our gauges are nothing more than over done idiot lights in most cases, and can read wrong. Only a true mechanical gauge will give you a correct reading.

 

it's not hard to drop the oil pan on a 4x4, I've done mine 2x
inspect the oil pick up and see what's in there.
mine was spotless, nothing anywhere but oil.
you can reuse the gasket, it's a good one.