Oil pressure gauge at 0 at idle
 

I noticed today that my 94 E320 oil pressure gauge is at 0 when idling and only goes up to 1 1/2 to 2 when driving. How can I differentiate if it's the oil pressure sender or the oil pump? I just change to oil last week.

Very unlikely to be the oil pump
 

since you would hear the sounds of very low oil pressure in an engine clanking away at idle. The sender is quite easy to replace.

You can verify the accuracy of the gauge by connecting a mechanical gauge at the oil pressure test port. Oil pressure sender is a common failure item, otherwise actual accurate oil pressure numbers as described means trouble.

<< The sender is quite easy to replace.>>

Just unscrew the old one and screw in the new one?

That's pretty much it Edge. Should be threaded into the lower part of the filter housing, probably in a tight spot. Should take a 17mm open end to loosen. Getting the replacement threaded in isn't terribly difficult, it just takes a little finesse to get started without stripping the aluminum due to being in a tight spot. Cost is ~$70 for the sender.

Ooops...just noticed this was the 6 cyl. Not sure where the sender is located. Don't these have the filter top mounted?

edit: I just looked at my EPC for the 94 320. It appears the filter is mounted in the classic position on the side of the block. Sender is mounted at the bottom of the filter housing. I wanted to take a screen shot for you but I have no printer and my laptop wouldn't permit it...unless I'm doing something wrong???

Replaced mine last year...five minute job.

Located just below the oil filter. Tight working area due to starter and some intake stuff occupying said space. A short wrench (7" or less) makes this an easy task...no room to turn a larger one!

Careful with the sender connection...the plastic has been subject to heat and age and is probably brittle...