Oil pressure sensor transfer function.

[Six_Shooter]

Does anyone have a chart or table that shows pressure vs. resistance of the typical GM oil pressure sensor used in the '80's and '90's?

I'm trying to make a digital readout for a couple of my gauges, I have the charts for temperature sensors, but not oil.

In the searching I have done, I keep finding information on LSx 0-5V sensors, which are not the same.

[Six_Shooter]

Well, I said "screw it" and hooked up an old Sunbird gauge I have kicking around and tested the resistance needed for each point in the indicated range.

Turns out, on an imperial scale (PSI), that 1 ohm roughly = 1 PSI. According to trendlines there's a SLIGHT polynomial curve to it, but the difference between a linear trendline and a polynomial trendline was very small. My gauge is in kPa, so I had to convert to PSI.

With a better set-up I'm sure I could get a better reading on that line, also using an actual pressure sensor for the readings would be more accurate this will at least get me in the ball park and shows me that I can use a simple linear function to get the desired output.

[1project2many]

The older pressure sensors are usually linear. They use a contact on a plunger to wipe across a wire wound resistor. Be sure to match the sender to the pressure range expected. This page has test points from GM documentation for several different gauge senders over a number of years:

http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.0

The Oil Pressure Gauge Needle Should Point to:
Left Line (Low, 0 PSI) when sender resistance = ~0 Ω
Middle Line (30, 40, or 50 PSI) when sender resistance = 30 Ω
Right Line (High, 60, 80, or 100 PSI) when sender resistance = 60 Ω

[Six_Shooter]

I actually found that thread last night before I did my testing and is where I got the values for the pot and parallel resistor from to test with. It wasn't until after I finished my testing that I noticed the indicated resistance values. Still, the range I found, while also linear(-ish) was still different than what the thread indicates for the applications it is intended for.

The kinda funny part is that after I was done testing and wrote most of the code that I needed that I realized it wasn't the oil pressure gauge I needed at this point it was a speedometer.... D'OH! Oh well, I can incorporate the oil pressure as well.

I've been using the TunerView II on my dash as my temperature gauge for about 2 years, and since the engine swap, it's been my only speedo. I want to swap to a different ECM for more testing of a different code and the TVII doesn't work with this other code, so I need to get some stand alone gauges going again.

[1project2many]

There's a huge variation in sensors and the accuracy really isn't that good. I can try three different sensors and get three different readings. Ford is worse. They put a switch on the gauge so you've either got "normal" pressure or "none." What a joke. Some aftermarket companies will list one sensor for 0-40 and 0-80 GM gauges even though there's no way one sensor can cover both. Oh, wait, unless they split the difference so the gauge reading can never be correct on either gauge. But as long as they show pressure, what's the problem?

Oil pressure can be nice to have. Now that the code's written might as well use it, right?

[RobertISaar]

i've noticed all of my 60V6 ones seem to be a fairly linear 0-90 ohm for their 0-80PSI range... they read accurately enough to notice the trend of when the oil needs changed(I would lose ~5PSI off of 30ish at full temp highway speeds). change the oil and do the same run, pressure goes back up to where I expect it to be. I guess that's handy without a trip computer or memory issues to keep track of oil changes.

beyond that..... I expect to see it show where the oil pressure relief valve is set at(60PSI) when cold, where the lifters start getting unhappy(around/under 10ish) and pretty much anything in-between is not too relevant.

I wonder how well the newer ones that keep track of oil pressure for better VVT/VCP control are?