1997 Ranger 4.0 4X4 oil pressure guage

[Sally88]

When the engine idles at a stop light, the oil pressure guage sometimes bounces. I added oil and checked the level to be correct, but it still does it on occasion. If I rev the engine to above 1000 rpm is doesnt. Any ideas on the problem?

[Coastie John]

My mom's 2000 Ranger does the exact same thing. I drove it today on a one day road trip for my first time. As soon as I got off the interstate and reached the first stop light, I noticed the oil pressure needle bouncing. The pressure never dropped, the needle just bounced a little in the "normal" range. When the rpm's increased, it quit bouncing. On the return trip, it did the same thing when I got to the first stop light after exiting the interstate. I played with it a bit while sitting at the stop light. In Drive the needle would bounce. In Neutral (rpms increase a tad), the needle wouldn't bounce. Back to Drive (rpms decreased a tad) and it started bouncing again. After a few minutes off the interstate, it would operate normal at stop lights. (BTW...this truck is in Daytona Beach too)

I'm thinking.....

1. Bad sending unit/switch
2. Electrical power problem to the gauge....loose wires to the back of the gauge
3. Possibly aerated oil getting to the sending unit/switch
4. An actual oil fluctuation....something real ugly



EDIT ADDED: I found this on another website. It sounds like a bouncing oil pressure needle is a common problem on some Rangers. Some excellent info here. This copy/paste is for a 3.0 engine. The 4.0 is located from underneath up front. Read all the posts to see the tips everyone is posting

http://www.topix.com/forum/autos/for...1AMIF1PTVO7E5I

Jan 19, 2009

I just successfully replaced the oil pressure sending unit (also called O.P. Switch) on my:

2000 Ford Ranger V6 3.0 liter 4x4 engine.

Symptom: Flickering oil pressure needle on dashboard gauge. Stuck on L when cold. After warm up, it clicks back to the middle, as normal.

The location was really hard to figure out, so I am posting it here to save others the time.

I found it at the back, passenger side of the block, accessed from the top, not the bottom of the engine. You can't see it from below.

From the top center of the engine, look at about the midpoint of the engine at the very back. Nearest thing as you go further back is the firewall. There are 2 switches back there that screw into the block. The OPSU is the one with a single (green and white stripe) wire. The other switch has a bundle of wires to it. You have to be on top of the engine, physically, looking straight down to see it.

At the auto parts store, though, there was significant confusion over what the part was and they sold me an "oil pressure switch" that had threads on both ends, and a grey barrel shaped plastic mid section. This wasn't the right one, despite what the computer said. Apparently, one sets off an indicator light and the other switch sends variable pressure info to the dash gauge. These might be backwards on the auto parts store computer.

After locating the switch and confirming that it directly affected the needle on the oil pressure gauge (by unplugging the wire), I noted that the electrical connection had a quick-connect, not a threaded ~1/8" screw (as on the first wrong switch). Once I got the right part, it was easy to replace with a deep socket spark plug socket and extended socket wrench with one of those hinged knuckles (because of the weird angle of the switch). My switch came with teflon tape already applied to the threads of the business end. There was no oil leakage during replacement either. 5 minutes total replacement time, 10 hours research to locate its position.

It cost about $9.

[Coastie John]

Followup: The new switched seemed to fix the problem. So far, so good.