Upon start up my 98 XLT V8 5.0 has a tapping sound that usually goes away after it warms up. I check the oil every time I fill up so I know the oil level is good.

Last night the oil pressure gauge started going crazy moving from high to low super fast. This was accompanied by the tapping sound.

I am going to pick up an oil pressure gauge and perform a test. What should the pressure be? Thats my first step. I dont know what to do after that.

Also, and I'm just shot gun maintenancing here, I was curious, if it ends up being the oil pump, has anyone ever removed one without taking out the engine. One maintenance manual says: "1. Remove engine. 2. Remove and replace oil pump. 3. Reinstall engine." Is it that the only way of getting access to the pump? I see its at the bottom of the oil pan but, sheesh thats a lot of work......

I had similar situation on my 92. In my case it was the oil pressure sensor switch. It's pretty cheap and easy to get at. I would try that first. Let us know what happens.

Wasnt able to get a oil gauge. Auto Zone and Checker said they dont have any, "and its only available at the dealer". Whatever. Anyways, got the oil pressure sensor switch from NAPA. Researched where its located at through this and other auto forums. Supposedly its "below the rocker arm on the LH side". Other forums give the impression that its a quick replacement job. I think I located it. IT is an SOB to get to! I'm not 100% if its Hours later: I still havent been able to remove it. The replacement part has a one wire connector on it. The existing part has a nub or nipple on it. I went back to NAPA, The parts dude got the nipple part for me. He says "Its for the light". WTF does that mean?! Am I missing something here? Am I eyeballing the correct part? The part I am attempting to replace is above the oil filter. It is so inaccessible, that I had to remove the oil filter and the lower radiator hose to be able to barely reach the wire to disconnect it. This is 5.0 engine. ARGH!!!

I don't find a good diagram showing the location, but according to the factory service manual for the 1998 5.0L Explorer, the location is "On engine, next to power steering pump."

The reason the parts guy said it's "for the light" is because typically an oil pressure switch is just to turn on or off a light, versus a sensor that is typically used for a gauge. Unfortunately, even though the instrument cluster in your Explorer appears to have an oil pressure gauge, it functions like a switch. When the switch is working properly you get either no oil pressure or "Normal" oil pressure, nothing in between or "high."

-Rod

Thanks Rod, good info. Well it got it replaced. BTW, of the three items I've replaced, that was the number one PITA of the three. The other two were challenging (fuel pump, radiator), but this kicked my butt. Oh and another kick in the butt: original problem still exists! ARGH! No oil pressure registers. While eyeballing the pressure gauge, I noticed something that I never noted before: before turning over to start, the pressure indicated mid range. Is that right? Like I said, I never noticed that before, not that I ever looked for it. So now I dont know what to do. I guess I'll fabricate an oil pressure gauge together and screw into where that PITA sensor is to gain a true reading. Other than that, I'm stuck.

Since you have a tapping noise that correlates with the gauge flopping around, you probably have an issue with the system.

The spec oil pressure is rated on an engine that's up to operating temperature. At 2000 rpms the pressure should be 40-60 psi. I would not expect the pressure to read at the midpoint until the engine is started, you might have a wiring issue for that gauge.

I don't find in the service manual specific steps for the oil pump. It's not listed at one of the "in-vehicle repair" options. However, it is listed as an in-vehicle repair for the 4.0L engines (pushrod and SOHC), so it doesn't appear to be an oversight or that I'm looking in the wrong place.

-Rod