'96 Oil Pressure Gauge Fluctuating

[90FoX]

Hello,

I was hoping y'all could help me figure out what's happening with my oil pressure gauge please? I was at the light the other day when I noticed the gauge moving around. It was only doing this at idle. Here's a link to the video I was able to capture:

https://vimeo.com/137334318

From my research, this gauge is either on or off and doesn't actually provide any real readings other than there is more than 6psi of oil pressure. Does this movement seem normal? I thought since it's on or off it should hold steady. Maybe my oil pressure sensor(sending unit) is going bad and cutting in and out? The gauge held steady with any amount of throttle.

I hooked up a mechanical test gauge and with a cold start up at idle it showed 90-95psi of oil pressure. Once warm, idling for 15+ minutes, it was showing 22-26psi at idle. When rev'd and held at 1500rpm it was showing 35+psi.

Is this normal? I searched and searched and can't find any specs for oil pressure at idle. I did see something about 20-45psi at 1500 warm is normal. I'm unsure if this is accurate or not.

Is there a way to test the sending unit? Or should I just replace it since I'm down there already? Maybe this is nothing to worry about?

Any help is appreciated!

Thank you. :beer:

FoX

 

[mwolson]

Disconnect the wire from the sensor. With the key on, engine off, you should see infinite ohms across the sensor. With the key on, engine on, you should see near zero ohms across the sensor.

With the key on, and the sensor disconnected, the oil pressure gauge should read zero. the the key on and the sensor wire grounded, you should see "normal" oil pressure on the gauge. With it still grounded, jiggle the wire to see if you can find an intermittent open in the wire.

If you want to make it a real oil pressure gauge, see this writeup: http://www.svtperformance.com/forum...r-79-98-oil-pressure-amp-temp-gauges-accurate

And those pressures seem ok to me.

 

[projectslideway]

Disconnect the wire from the sensor. With the key on, engine off, you should see infinite ohms across the sensor. With the key on, engine on, you should see near zero ohms across the sensor.

With the key on, and the sensor disconnected, the oil pressure gauge should read zero. the the key on and the sensor wire grounded, you should see "normal" oil pressure on the gauge. With it still grounded, jiggle the wire to see if you can find an intermittent open in the wire.

If you want to make it a real oil pressure gauge, see this writeup: http://www.svtperformance.com/forum...r-79-98-oil-pressure-amp-temp-gauges-accurate

And those pressures seem ok to me.

I would start by doing these recommended electrical tests.


If it turns out to need an oil pressure sender (switch) please be advised that myself and a few others have actually needed a replacement switch from a GT and NOT the Cobra spec switch. That being said, I have two Cobra switches laying around if you need one because the GT switch was what I actually needed.

 

[90FoX]

Hello,

Thank you for your responses. I will definitely try out the tests described above. Just to clarify, when testing the resistance of the sensor one lead from my multimeter should be on the contact where the gauge wire plugs on to the OP sensor and the other lead should be grounded?

Also, does anyone know if my tested oil pressure is good? Is there a source which provides the psi specs for oil pressure? I'm surprised that I can't find this info online after much research.

Thank you again. I'll post back later this week with my findings.

 

[mwolson]

You got it right. Test the sensor with an ohmmeter across the stud and ground.

Your oil pressure is nearly identical to mine. As I said it looks good to me. I have never seen specs.

The stock Ford sensor is a 6 PSI switch, so you could consider 6PSI as the spec maybe.

 

[cbrown9064]

That oil pressure seems OK. Close to what I see on a Autometer gauge.

 

[90FoX]

Hello,

Mark: you're right. Not sure how i missed you mentioning the oil pressure was good in your first response. Sorry about that. I ran the tests you suggested and everything seems good. Gauge holds steady when fed a ground. Wiggled wires and no movement in gauge. Switch shows infinite ohms when key on engine off and very low resistance when engine running. I think I'll swap the switch for a new motorcraft oem unit since I'm down there and it's only about $20.

Since everything is testing fine I'm confused what the issue could be. Any suggestions?

Project slideway: thank you for the heads up. You're totally right. Wth is the unit in my cobra the gt unit? So confusing. The one in my car looks like this:

http://www.fordparts.com/Commerce/P...search=true&year=1996&make=Ford&model=Mustang

And the listed switch for a cobra looks like this, nothing like what's in my cobra right now:

http://www.fordparts.com/Commerce/P...search=true&year=1996&make=Ford&model=Mustang

Should i just pick up the gt one since that is what matches the one in my car?

Cbrown: thank you for confirming the oil pressure you see in your car. Matches Mark's too. I think it's safe to say my real oil pressure is normal.


Thanks again for everyone's help.

 

[projectslideway]

Project slideway: thank you for the heads up. You're totally right. Wth is the unit in my cobra the gt unit? So confusing. The one in my car looks like this:

http://www.fordparts.com/Commerce/P...search=true&year=1996&make=Ford&model=Mustang

And the listed switch for a cobra looks like this, nothing like what's in my cobra right now:

http://www.fordparts.com/Commerce/P...search=true&year=1996&make=Ford&model=Mustang

Should i just pick up the gt one since that is what matches the one in my car?

The one that is in your car is the same unit that was in my car from the factory. It had the white plastic cover just like in the picture.

The updated replacement switch for Cobras looks like the link you posted. I tried two of them with no luck.

The exact GT switch looks like this...

http://www.autozone.com/external-en...96/8-cylinders-x-4-6l-sfi/966611_652058_8450/

The picture is accurate, it's a standard wrench size and doesn't need a special socket like the Cobra unit.


If I were you, I would pick up both and figure out which one works for you while you have the car jacked up and return the other. I would start with the GT switch.

For the price of the Valucraft stuff you can try both for the price of a Motorcraft unit. Just remember you will need to have some teflon handy.

 

[mwolson]

The first thing to suspect is grounds and connectors. Since the ground is taken care of with the pipe threads, the next thing I would suspect is the connector. You might want to try putting a bit of aluminum foil over the stud before you plug the wire onto it. That will shim the stud a bit, making the connector fit tighter. An intermittent connection at that connector could cause the issues you are seeing.

 

[90FoX]

The link to auto zone doesn't work on my phone for some reason. Is the part number PS164VC?

Did you try the sensor with the white cap? If so, it didn't work? I would think that the white one should be the same as the auto zone one. They are both for 4.6 2v. But if you've tried it there must be a difference.

Mark that's a very good point I'll give the foil a shot and check to see if I can squeeze the connector tighter.

Thanks!

 

[90FoX]

Hi everyone,

I wanted to post an update in case someone has a similar experience, this might help.

I went ahead and picked up the following oil pressure switch, the white cap Ford oem switch:

http://www.fordparts.com/Commerce/P...search=true&year=1996&make=Ford&model=Mustang

The Ford part number is sw-2220 or as listed on the ford parts site "part Number: 9278(SW-2220)"

It looks identical to the switch that i replaced and so far after about 100 miles the gauge has held steady and seems to be okay, no more bouncing. I'd say it's resolved but want to drive a bit more and see if the issue reoccurs as i only noticed it once.

The switch seems to come with red thread sealant already on the threads but i still applied some permatex 59214: high temp thread sealant. It's intended for use with oil pressure switches and hydraulic applications.

Thanks again for everyone's help.

Ps- remember not to over tighten. You don't want to damage anything or ruin the threads in the oil cooler. Also you don't need any special socket to remove the switch. A 1- 1/16" wrench or crescent wrench will do. I tried the special socket and couldn't get it on the switch because the socket is too long and something is in the way.

 

[Whit Clark]

yeah ill have to try all this out on mine as well. i replaced mine with a Cobra one and still drops as i it were off and then once in a blue moon itll actually be straight up like it should. good info guys.