1989 Bronco 2 sounds like a diesel.

[Maximus]

So here is whats happening. When I start my vehicle first thing in the morning it runs awesome. Sounds great, runs great, oil pressure is perfect, great amount of power for such a small engine. After its warmed up and I pull up to a stop, it sounds like a diesel engine. Oil pressure fluctuates, sometimes down to zero. I give it a small amount of gas, doesn't sound like a diesel anymore and the oil pressure returns to normal. Also once its warmed up and I go to shift gears, let up on the gas and engage the clutch, it seems to rev up slightly and sound like a diesel. But under constant power like at highway speeds, it runs smooth but lacks power a bit. Also, not sure if this is connected, but while accelerating after its warmed up, I lose power almost exactly at 2000 rpms and it comes back almost exactly at 2500 rpms. But it doesn't do it when the engine is cold.

 

[RonD]

When you start a cold computer controlled engine, the computer runs in Open Loop and Choke mode.
Computer gets coolant temp from the ECT sensor, this is a 2 wire sensor near thermostat.
There is also a 1 wire Sender near by, this is for the dash temp gauge.

When ECT sensor shows cold coolant computer runs engine rich with high idle and advanced spark timing, just like Choke did on carb engines
Choke mode

O2 sensors don't work when they are under 600degF, so computer ignores them until they warm up, this is called Open Loop(or no loop, lol) since computer has no feedback that engine is running Rich or Lean.
Once O2 sensors are working computer switches to Closed Loop.
Closed Loop is when computer adds fuel then sees what O2 sensors says, if Lean computer adds more fuel, if Rich less fuel, so computer is in a Loop, a closed loop because it is getting instant feedback on fuel being burned.

Diesel engines ping, so I assume you mean your engine is pinging.

Pinging can be caused by Lean fuel mix, overheating or incorrect spark timing.
And if it only happen in Closed Loop then O2 sensor could be at fault.

You didn't report overheating so that should be off the table.

Lean fuel mix could be low fuel pressure but I would think you would notice lack of power the faster you went at highway speeds, i.e. fuel pressure drops off more as demand increases.
Lean mix can also be a vacuum leak, or IAC Valve issue, I would clean IAC valve, not hard to do.
IAC(idle air control) valve is used by computer to set idle RPMs, computer sets idle above 1,100 when coolant is cold, and then slowly closes IAC valve as engine warms up dropping warm engine idle down to 600-650 for manual trans.
If you unplug IAC Valve on warm engine idle should drop to 500 or engine may stall, either is good it means IAC is working and no vacuum leaks.

You have a TFI spark system, which at this age should have been serviced a few times, maybe it is time again

Good read here on TFI system: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

To set base timing you need a timing light and you need to disconnect SPOUT connector.

1989 2.9l may only have 1 O2 sensor, and they last about 100k miles.
But even if it has 2 O2 sensors one could be causing the pinging in Closed loop if it is giving Computer wrong info on Lean/Rich.

 

[Maximus]

I had to reread my post a few times to make sure I was clear and what I posted was understandable. First, I live in Iowa and lately its been pretty cold in the morning. So warming the vehicle up takes a bit longer. That being said, When the vehicle is first started, it only stays at high idle for about two minutes then drops to normal. Vehicle runs great until the engine is completely up to temp. LONG after the high idle drops down. I said the vehicle sounds like a diesel, maybe I should have been more clear. It sounds like a loud diesel with no oil in it. The problem is in the oil pressure, not fuel. After the vehicle warms up completely to temp, when I come to a stop the vehicle oil pressure drops... sometimes to zero and it sounds like a loud diesel with no oil, but it doesn't stall nor does it act like its going to stall. But if I give it the slightest amount of gas, oil pressure goes back to normal and it doesn't sound quite as much like a diesel. Oil is full and it doesn't use any fluids. Coolant is not leaking into oil nor is any coolant or oil leaking.
Now here is a small update, took advice from a mechanic friend, changed the oil to 15W40 and put a quart of lucas oil stabilizer in it. I started it and then took it for a drive. Vehicle runs perfect almost all the time now. After it warms up it still has a small sound like a diesel but oil pressure doesn't fluctuate. He said it may be the main bearings or the oil pump, or both. Cant tell for sure until its tore into.

 

[RonD]

Yes, that reads more like valve train clatter than pinging.

Oil pressure is back pressure.
The oil pump creates a flow of oil from the oil pan pickup thru the oil filter and to the main oil passage(where oil pressure sender is).
When this flow of oil splits off to smaller passages and gets to the bearings, mains and connecting rods, the gaps are too small for all the oil to get out so Back Pressure builds up in the main passage.
General rule of thumb is 10psi of oil pressure per 1,000RPM, up to about 60psi where high pressure valve(ball with spring) in oil pump is pushed open to relieve the higher pressure.

At warm idle most engines will be at 6-8psi, 600-800RPM idle
Ford uses an oil pressure SWITCH on the engine, on/off, it is set for 6psi, below 6psi switch is OFF and oil gauge will show 0psi, above 6psi switch is ON and gauge will show "normal" pressure, any movement of the gauge in "normal" area is voltage related not oil pressure related, just FYI.

With minimum of 6psi oil pressure there is enough pressure to feed the valve train at top of engine, when you get down to the 4-5psi range the valve clatter will start.

If you run a "thicker oil" then Back pressure will increase, oil pressure will increase.

But why was it low in the first place?
Yes, could be a main, rod or cam bearing is worn so has a larger gap, which means more oil can flow thru that gap and so back pressure in the whole system goes down.
Think of a Soaker hose, if you were to poke a larger hole somewhere in the hose then flow would be less to the smaller holes, because back pressure has dropped.

yes, for oil pump as well although they usually last the life of the engine, could be spring on high pressure relief valve is loose or ball has some gunk in it causing it to leak, so flow is less than it was.