Oil Pressure Gauge Question

[Backlash2032]

Okay, so shortly after my rebuild, I noticed an odd quirk. Almost exclusively when I drive on the highway, I notice my oil pressure shoot sky high. Pegging the gauge. I know this is obviously not an accurate reading... Since the relief valve would be at ~80 psi and the filter would have blown up a long time ago at those pressures... So judging by the TSRM way of testing the gauge, saying shorting to ground will make the gauge go to the high side, would I be correct in saying I have a short to ground somewhere?

And I remember somebody saying that if you shorted the gauge to ground for too long that it would melt part of the gauge? I think it was JJ who said that.. Anyway.. I'm just wondering this because it worked fine before the second time it decided to go to 120+ psi, and now it reads insanely low. Like going down the highway at maybe 1 psi low. I figured it was the gauge being ruined so I didn't think much of it. Now i've been put probably 800 miles on it with "0 oil pressure" so it definitely would have blown up by now. So I have oil pressure.. So would the short have ruined the gauge? Or do I just have a bad gauge?

 

[Hotwheelsjr]

Sorry I don't have an answer for you. I have an after market (Pro Sport) electric gauge and it does the same thing. When cold it appears to work correctly -- 45psi or so when I first start the car. As it warms up and I start driving my pressure is ridiculously low and 0 at stops. There are times when I am driving I'll look down at it and it's pegged at 150 psi and then it sweeps to zero. I was thinking maybe a bad sending unit. I bought the gauge a while ago and have yet to contact Pro Sport about it... I have a separate oil temp gauge and it works fine.

 

[SupraStoked]

go mechanical, much more simple and reliable. yea they might not be as fancy but its accurate and does the job

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[jetjock]

^ Yea...simplicity, accuracy, and reliability are why mechanical instruments are still used in airliner cockpits.

OP: The gage can be tested per the TSRM...

 

[Backlash2032]

Well the thing is, it only spikes intermittently. So if that's a short in the wire between the sending unit and gauge then throwing a new gauge on it because it fails the tsrm tests means that gauge would be ruined with a quickness.

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[SupraStoked]

I'm not sure but why even deal with electrical gauges?? mechanical is just plug and play and you wont have to worry about any of that. as long as you hook it up right, it will work

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[Backlash2032]

And then what if it springs a leak? 180*+ oil all over the cabin. Sounds like fun to me.

Besides. I hate when the factory gauges don't work, and then people throw aftermarket gauges on it. I don't care how inaccurate the factory gauges are, I want them to work too lol

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[SupraStoked]

the only way it'll spring a leak is if you undertightened the compression fittings or if you bent the nylon tube at too sharp of an angle. but yea, I know what you mean but I personally hate. messing around with electrical crap lol

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[Backlash2032]

Lines fail too.. and I find Electrics fairly easy. Just need a little help. Like now lol

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[CyFi6]

So the gauge used to read normal sometimes and randomly spike sometimes, but now it reads 0 all the time? Test the gauge and replace it if it is bad. If it spikes again then you need to figure out the source of the problem before you blow another gauge. First thing I would do if it continues to spike is disconnect the terminal from the sender and see if it does it again. If it still spikes with the terminal disconnected then you know its a short in the wiring, if it stops you know the sender is shorting internally.

 

[Backlash2032]

I'll disconnect the sender tonight and see if it still spikes. I don't know why I didn't think of that. Thanks

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[jetjock]

Any mechanical gage setup worthy of the name will have a safety orifice. That said I was being sarcastic about mech gages. They're old tech that are far less reliable and accurate than a decent electric. And the stock gage can be made to be accurate assuming it already isn't. Its downfall is response time.

 

[Backlash2032]

I've already noticed the lack of response time. lol How do you make the stock gauge more accurate? and would you be able to do the same with the stock coolant temp gauge?

 

[Backlash2032]

Well I haven't gotten around to disconnecting the sender. But I did take the cluster out and ohm out the gauge. and it specced in at ~40 ohms, which I would assume is close enough.

Since I had the cluster out though, I decided I would do the tach resistor swap so it works (N/A -> GTE swap) and after getting it all together, tach works. Idles at ~700-800 rpm. But when I gave it the beans it rev limited at approx. 5700 rpm. Not even up to the redline. This is on a post 89 ecu so it has the lower rev limit. I just thought it was odd that it seems fine at idle and just cruising around town, but once up in the rpms it gets off.

This is the guide I used:

Edit: I forgot to mention that I had every resistor exact except for R1, which I soldered together a 120k and a 10k resistor. Not sure if this would affect anything.

 

[Backlash2032]

Okay. So I disconnected the sender for like 2 months. Zero gauge movement. Never spiked to 120 psi. So that would mean the wiring to the sender is correct. Right?

Where else should I look?

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[jg5899]

Seems that would indicate a faulty sender.

Not to jack a thread, but out of curiosity does anyone know if tapping into the oil pressure sender wire if that would cause an inaccurate reading? I had that issue with a coolant sensor, and was wondering if the oil pressure sensor would yield a similar issue.

 

[Dan_Gyoba]

The sender wire shorting to ground will spike the gauge.

Also, my tach (NA->T swap) indicates about 5500 RPM when it hits the rev limiter. Verify your stock tach against a diagnostic tach, I think you'll find that yours is wrong.

 

[Backlash2032]

I was talking to Aaron from driftmotion and he was saying that the sender could not produce those symptoms.

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[jetjock]

It certainly can. Although how this particular sender/gage operates is unique compared to others it's still not difficult to test. As I said in post #4 start by using the TSRM procedures.