Variable Oil Pressure Gauge Modifiction

[DILLARD000]

Buy Cluster with DarkGray Gauge BackGround, so that 4WHi & 4WLo icons don't show;
then just don't install 4WHi & 4WLo indicator lamps for your 2WD truck.
Unsure about Cluster mods for converting OilPressureNeedle from On~Off to a true VariableGauge.

 

[Stinky_Sullivan]

Welcome to TRS

Yes, you can use 1996-2003 cluster to replace 1999 cluster, 2WD or 4WD doesn't matter, or manual/auto

But where is the resistor that requires the bypass on this 2000 4x4 cluster? It’s not the same as the one in the How-To.

 

[RonD]

I don't think it can be done on later clusters, 1996 and up
But never tried myself

 

[Stinky_Sullivan]

I don't think it can be done on later clusters, 1996 and up
But never tried myself

I have no doubt the oil pressure gauge works the same on both clusters. The technology didn’t change. The only question is which resistor to jumper.

If I had a ‘95 Ranger and I were to replace the oil pressure switch with an oil sending pressure sending unit without jumpering the resistor, what would happen?

Likewise, if I were to jumper the resistor without replacing the oil switch, what would happen?

the answers to those questions will help locate the resistor in the oil pressure gauge circuit.

 

[RonD]

PS60, or similar pressure sender is a variable resistor, vs a pressure switch sender which is on/off

They both use the vehicle Ground as the control, i.e. oil gauge gets 12volt with key on, if gauge is not grounded by sender then it shows 0 pressure

When there is oil pressure above 5psi, the switch sender is on/closed, grounded, so that ground passes thru the cluster's resistor and oil gauge gets a "partial" fixed ground, and gauge shows 1/3 to 1/2, depends on vehicle voltage 13.5 to 14.5volts

The PS60 is also a resistor, but resistance changes with oil pressure, low pressure is high resistance, higher pressure lower resistance, like a volume control or light dimmer
If used in line with clusters resistor the gauge needle most likely would stay on 0 since the Ground resistance would be too high to get any movement
If you REVed the engine to get higher oil pressure, so PS60's resistance value dropped, you "might" see some movement of the needle, but under normal operation it would just stay at 0

When Ford switched to the oil pressure switch in the late 1980s it was to stop the silly customer complaints of low oil pressure, and it worked

So after 6+ years they decided to stick with the switch(on/off) setup
And it was my understanding that in 1995, when the clusters were redesigned, the newer oil pressure gauges had an internal resistor, so no external resistor was used, so no way to "jumper it"
1995 was an oddball year for clusters, different than 1994 and 1996, so it may or may not have the external resistor, I don't think 1996 and up had it


Oil pressure is the oil the engine CAN NOT USE at that moment
You are seeing the pressure in the main oil passage as it builds up because the bearings and valve train can not use it, its BACK PRESSURE
Engines need a minimum of 5psi back pressure to over come gravity to keep valve train lubed, under 3psi you will usually start to hear "ticking" from valve train
Ford's pressure switch is set at 5.5psi, +/- 0.5psi
At higher RPMs more bearing cooling is needed so a higher back pressure is good, above 30psi is fine, anything more is just for "show", lol
Above 70psi and you can "wash" bearings, basically they can run dry because oil is spraying in/out too fast so is not coating and cooling the bearings, it turns into a "mist" instead of a stream, and you get spun and failed bearings

 

[Stinky_Sullivan]

There are some assumptions there which mean they’re not certainties. But let’s conclude they are.

The gauge on the ‘96-later cluster with no tach rotates in a clockwise direction while the cluster with a tach rotates in a counter clockwise direction. Likewise, the gauge on the ‘95 cluster rotates in a counter clockwise direction. Can the functional part of the ‘95 gauge be transplanted to the ‘96 cluster with the tach? That would give the ‘96 tach cluster a non resistored oil pressure gauge.

 

[RonD]

You would need to pull the oil gauge and give it 12v and a ground, if needle goes to full then it uses an external resistor
If it goes to 1/3-1/2 then its an internal resistor

You could install a separate gauge on A pillar, digital oil pressure, digital temp and digital volts are very good to have
Needle gauges are OK but if you want info you can't beat actual NUMBERS, lol

 

[Stinky_Sullivan]

I can definitely test my cluster for the internal resistor. I don’t mind going with the A-Pilar mounted gauges if someone makes a Ranger specific A-Pilar trim piece for those gauges. FWIW, I prefer analog over digital.

 

[Elutheros]

I just happened to have my dash torn apart to install a Vintage Air A/C system so I'm doing the mod on my 1992 and I already had the new sender unit sitting in my spare parts (since it didn't give a trustable reading without the mod I had installed a mechanical gauge). Thanks for the write-up!

 

[ratdude747]

Surprised to see people are still commenting on this... go figure. Swung by here to link it to a discussion on a different forum involving relocating oil pressure sensors with pipe fittings.

Still own and drive the 1995 4.0... and the oil gauge still works great. The only "issue" I've had was for some reason in a traffic jam last weekend my idle kept dropping to 500rpm or so with the A/C on and both my battery and oil gauges started dancing. Oil level was fine (the 4.0 leaks a bit, and probably burns a bit too). Once at speed there were no more issues, thankfully... and it hasn't done that since (may be related to the 130A alternator and PWM E-Fan swap I did, but that's another discussion). Edit- That's probably an IAC valve issue per another thread. Not a gauge fault per se.

One other thing I'll note: If I were to do this to my 4.0 again, I'd probably just get a replacement connector pigtail for the sending unit and splice it in rather than using ring terminals and bolts. I had to replace one of those connectors on my 1984 F150; the engine was out for a rebuild and as part of the engine removal I found the dashboard coolant sensor connector was wasted; a PO hacked up a lot of the wiring (stripped insulation to test ) and that was one of many connectors too far gone to save. IIRC it wasn't expensive if one shopped around ($10 I think?) and would in hindsight result in a cleaner install. Not that I'm looking to fix what ain't broke on mine (unless/until the day comes that I find one not rotted away and start swapping things, that is).

 

[I support common sense]

I know this thread is three years old, but this seemed like the best place to ask. I have a 99 ranger, and I swapped out my dash for one with a tach from the same year. I want the variable oil pressure gauge, but I can’t find the resistor. I took the cluster apart all the way down to the serval motor and I find no resistor. I hooked it up to twelve volts on the b and g terminals then put twelve volts to the s terminal and the gauge comes up to the normal zone. The gauge does not appear to have a spring but as soon as I remove power it drops down to low it feels as though it pushes against the stop point. Someone mentioned that some of these only operate halfway up the dash. I wonder if perhaps the gauge is twisted halfway in the opposite direction so that when power is given it can only go halfway up. If I were to remove the needle and reset its position it may work just fine. Am I thinking correctly on this?

edit: Well, I quickly realized my fallacy. I took it all apart and adjusted the gauge and either way it will only operate on half of the scale. Now I’m wondering if I could buy an oil pressure gauge from and eighty seven ranger and swap out the servos. Or I still have my old dash and I might be able to use the amperes guage off it and add a resistor and swap the servos. Will an eighty seven ranger guage work?

 

[Cool Javelin]

This was written based on a request from this thread: http://www.therangerstation.com/forums/showthread.php?t=164957

The pictures were taken over a month after I completed the install. I did this based on some other sources, mainly http://www.rowand.net/Shop/Tech/FordOilPressureGaugeFix.htm

The point is that I am not the first to do this mod on a Ford vehicle or to post about it, but I am the first to document it here on TRS in the form of a tech article submission.

Other notes that weren't relevant enough to include in my write-up:

-I also read on another forum that some F150's with tachometers have gauges that only work for half the needle travel (IIRC it was 1995 and later) and the fix was to swap for a gauge out of a non-tachometer cluster of the same vintage.

-I have heard that sometime after 1997 the oil pressure gauge circuit went solid state and this mod was no longer possible. However, since my one and only Ranger I have ever owned or worked on is my 1995, I personally do not know. The next time I'm at pull-a-part on a nice day with some spare time, I may pull a couple 1998+ clusters and look to see if the resistor is present (and not take them out of the yard, as that would be wasteful).

-The main reason this works is Ford didn't change the gauges in 1987 (all they did was swap the sensor and add the resistor) and after that they didn't change the circuit (even with the new interior in 1995), which resulted in unintentional reverse compatibility.

-Oddly enough there are some test points on the cluster that can be shorted to do the same thing (easter egg from the engineers?); however, I (and the article linked above) didn't like the look of such as a place to solder; I found using the resistor crimps to be a better place to solder the jumper.

I made the change, and noticed the solder jumpers sections. I recommend you DON'T touch the PCB with a soldering iron. The PCB is plastic, and the iron will pretty much melt it away leaving only the copper traces.

In fact, to solder across the 20 Ohm resistor, I recommend cutting the resistor near the resistor body, bending the leftover leads a bit, and soldering a wire to the leads a good distance from the PCB. If you have hemostats, I'd use them a heat-sink to further keep the heat away from the PCB.

Mark.

 

[Cool Javelin]

Just to add a little detail, My "oil switch" failed and I wanted to upgrade to a real gauge.

Since I wanted to make sure I really had oil pressure, I measured it with a gauge (I removed the sending unit, and screwed the gauge in place,) and I measured about 45 - 50 PSI. I was pretty happy considering the motor has 250K miles on it.

I removed the cluster so I could jumper the 20 ohm resistor, and while I was there I ran some tests on the gauge reading vs resistance measurements, Here are my results... I will include pix, below, sorry about the glare.

115 Ohm = min reading (red line)
51 Ohm = min scale
23 Ohm = mid scale
12 Ohm = max scale
10 Ohm = max gauge

Note, the needle can be driven beyond the painted lines, but I tried to not do that.

I got a WS1547B from Amazon, They say the manufacturer is "Rivet-Line" It seemed to be sketchy as in I expected 50 psi to read mid reading or about 20 Ohms,
but with the 20 Ohm in series, the gauge barely showed min reading, and with the 20 Ohm shorted, it read Max scale.

Here are some resistance measurements for the WS1547B...

0 psi open
5 psi 34 Ohm
10 psi 33 Ohm
20 psi 22 Ohm
30 psi 20 Ohm
40 psi 17 Ohm
50 psi 15 Ohm
60 psi 14 Ohm
70 psi 11 Ohm
80 psi 10 Ohm

I got a real WS1547B from Autozone, and it seemed broken, it acted more like a switch, but also seemed unreliable. I returned it.

I tried a PS60 from Amazon, (It looked like the WS1547B in form factor,) but I'm pretty sure it is a switch. (I guess that is expected) (PS60 - Pressure Switch 6.0 lb?)

Anyway, I ended up replacing the 20 Ohm resister with about 7 Ohms, and that put the needle almost exactly in the middle of the range. (I guess a 7 Ohm (resistor) in series with a 15 Ohm (sending unit) is about 22 Ohms (mid scale))

It now seems to work as I want.

Mark.