Oil pressure low 1994 f150xlt 5.8l v8
 

I have a 1994 F150XLT 5.8L V8 EFI. Ive driven it for about a year now and originally the oil pressure gauge sat straight up and down but now it fluctutes between the "N" in normal and tge low end of the white safe zone box. I was going to try and replace the sending switch but cant seem to find it forward of the oil filter like i saw on youtube. Ive got about 180K miles on this and as far as I know the truck has done nothing but light travel with strick maintenance to the engine. I dont hear any knocking or rattling but the low pressure has me spooked. Oil is nice amber color. No water. A smidge over the full mark and ive been changing it every 3000 miles or sooner. It doesnt do any major hauling heaviest thing its ever had in the back is maybe 400lbs. Just back and forth to work.

It maybe necessary to remove the oil filter to see. Don't try to reuse the removed filter when done. It may leak, just replace it.My bet is on the sender too.Engines will get noisy when the oil pressure is too low.

Chances are you have a connection problem. 87+ Don't have an oil pressure gauge, they have a glorified idiot light that looks like a gauge. The switch on the engine is just that, an on\off switch. Once it hits roughly 7PSI, it's on. There is a resistor on the back of the gauge cluster that reduces this "On" (+12v) voltage to roughly 4-5v, which will show the gauge about half way up. You can change this though. You can pick up the oil pressure sender from a Pre-87 truck (5.0\5.8 require an extension to clear the PS\AC bracket), then bypass that resistor on the back of the cluster. From there, you'll actually have a function oil pressure gauge.

On my 87(300), many years ago, I installed a gauge sender in place of the stock "switch" and had a perfectly functioning gauge. Don't know differences between engines butyou might not have to mess around behind the dash.

It may work, but the needle won't go as high as it should, the resistor reduces the sender's output.

Between
Half three quarters up when cold and settles at the half way mark when warm at 2000 RPM.. I did this 15 years ago, no problems up to this point. Can't be happier with the results.That resistor is for the stock sender which is either a short or open (a switch) like you said so that the indicator falls in the middle.. A gauge sender is a variable resistor depending on pressure. Big difference.

Oh I understand what the sender and switch differences are. I'm talking about a resistor that is physically on the cluster itself. Here's a pic of what I'm talking about. Something must have happened to yours, or it was bypassed by someone else. If nothing was done during the swap, then your gauge would have been pegged full at all times, as the gauge would be receiving a full +12v all the time. Your situation is strange for sure, as the stock switch has no internal resistor at all.
Attachment 568145

Must not applied to 87's. I am the original owner, nobody removed the resistor or worked on the dash and my gauge has worked perfectly for 15 years.. That's all I can say.