Faulty Oil Pressure Sensor (?)

[smr1618]

Hello all,

For some context, my oil pressure gauge on the dash cluster does not work. I recently was doing some maintenance on my truck and noticed some damage to what I believe is the oil pressure sensor (see photo). I was unable to find this part in any manual I could find, but figured it was the oil pressure sensor due to its location under the filter. When looking online for a replacement they look similar but I am not positive. Can anyone weigh in and confirm/point me to a relevant manual?

Thanks in advance,
Sam

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28653&stc=1

[akrockin]

Yep, that's the oil pressure sensor. I've had a couple of them fail in the last couple years, never a good feeling when the oil light comes on. It's been awhile, I don't remember if the light should be on with the connector grounded or open. Someone else may know and chime in. If that's how yours looked originally I'd recommend cleaning up that contact and plugging the connector all the way in, the switch may still be good. You could also remove it and use an ohm meter to test the switch, I think (Don't quote me) with the plunger depressed there should be no resistance, plunger out there should be a high resistance / open circuit. I believe the switch gets it's ground through those threads, that could also be the issue. Good luck, hope you figure it out.

[SubGothius]

The low oil pressure warning light switch is a separate unit from the oil pressure gauge sender. In the photo you can see the other one off the side of the tee.

Typically the switch will be the smaller of the two, just a hex fitting with a terminal sticking out of a bit of plastic on the end, whereas the gauge sender will be a bit larger, with a small (2" or so) metal canister between the hex fitting and the terminal. Hard to tell for sure, but seems like both in the photo may be the switch type, which might explain why a prior owner just left it disconnected if they replaced the original gauge sender with a switch by mistake.

Both work by grounding their respective wires from the light or gauge to the block thru the switch/sender body. Oil pressure holds the switch open, preventing the light from illuminating, and pushes a plunger in the sender that presents a variable resistance for the gauge to read (it's basically just an ohmmeter).

OEM gauge sender part nos. should be MD005480, superseded by MD092660; aftermarket replacements will prolly cross-ref both. Oil switches and senders are both stocked at RockAuto for your year/make/model under Electrical-Switch & Relay > Oil Pressure Sender/Switch, and note which ones say light vs. gauge.

[smr1618]

Thanks a bunch. Was wondering why my searches returned 2 different things. The warning light is not on, so seems like the smaller one in the back is the light switch. I'll get a gauge sender ordered instead.

[smr1618]

Wanted to follow up on this as I’m a bit confused. Have the new part in hand and was getting ready to disassemble, but the old faulty sensor has a 3-pin connector, while the new part/all documentation of these cars stock is a single spade terminal. There is an aftermarket pressure gauge in the cabin, is it likely that somebody modified this harness? Even the light switch sensor has 3 connections oddly enough.

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28654&stc=1
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28655&stc=1

If it’s aftermarket guess the next step is to pull the gauge in the cabin and follow the wires/remove them and revert it.

[camoit]

the one in your hand looks factory. The 3 pin one is a gauge and oil light in one. But it doesn't look factory.
There is something else going on there because I see a T and another light switch.

[EL.95MAX]

the 3 pin one is definitely aftermarket gauge

[SubGothius]

I wonder if the extra pins support fail-safe interaction between the light and gauge, so the light going on also pegs the gauge, and the gauge passing a certain point also triggers the light?

[smr1618]

They are both 3 pin oddly enough, but the light switch sensor has 3 spade connectors not a DOHC.

[smr1618]

I was wondering if it was a lock/fail-safe as well, however the light is not on in the cluster and the gauge has no readout so I don't think this is it. I will have pull the after market setup and replace both sensors it seems like/revert it to single cable. I haven't checked behind the dash yet, it should be a single spade terminal at the gauge as well then??

[SubGothius]

Pretty sure for all years the stock-type light switch and gauge sender should each have one spade terminal, wired directly to the light or gauge respectively.

That setup you've got looks like a BSPT-to-NPT thread adapter (stock threading is BSPT), apparently to add a NPT tee to that, then the two switches (?) screwed into that tee, so some sort of jerry-rigged aftermarket setup there for some reason.

[smr1618]

Got the other sensor in and finally have some time the next couple days to tear those out and revert it back to original. Appreciate all the help from everyone.

[smr1618]

Finally getting around to this. I just noticed SubGothius you mentioned the T was not original. From pictures I have seen of other engines I see that now too. I am curious where the gauge sender threads in if only the warning light switch threads in below the oil filter? Cannot seem to find any unoriginal bolts in the block where it used to be or a faulty gauge sender itself.

[SubGothius]

Looks like there's just the one bung for a gauge sender or light switch, so trucks equipped with a gauge would have just the sender installed there and no separate switch:

https://www.megazip.net/zapchasti-dlya-avtomobilej/mitsubishi/truck-4388/k13t-10549/unslf-163666/oil-press-switch-or-gauge-unit-1865220

Prolly the gauge itself does double-duty to trigger the warning light when it's pegged at 0.

Speaking of double-duty, another thing just occurred to me about that 3-terminal connector on your apparent non-stock busted switch: could be that one terminal is a normally-closed circuit for the light, and the other two are a normally-open circuit for use as a safety switch -- e.g., to cut power to an electric fuel pump when the engine dies, such as in case of a crash.

[smr1618]

Okay I was thinking it would just be the gauge sender too then wanted to confirm with someone who knows more than me. & I agree about the aftermarket connector. I tried swapping the sensors and left those unplugged and it bogged out and wouldn’t start again. Must be hooked up to an aftermarket pump/regulator setup too. Will have to find a way to bypass that if I want to use the gauge

[SubGothius]

Disconnecting the oil pressure switch/sender shouldn't normally affect the engine running, so I'd suspect they're wired thru some sort of power cut-off to the fuel pump as a safety feature, prolly via a relay somewhere.

Engine may have started and briefly ran with whatever fuel was already in the carb bowl, but then starved out without any fuel getting pumped to the carb.

[smr1618]

Was thinking the same about the float bowl. I’ll see if I can sus out a relay or wiring. Thanks

[smr1618]

Given my more recent issues getting the car to run Ive gone through all the PO's electrical work. The 3 pin connector that wasnt attached to anything was for the aftermarket gauge in the cabin, which oddly wasnt hooked up to anything but power. Explains why it always read 100%. The 3 spade connectors on the sensor that was attached to the T fitting are seemingly also for an aftermarket sensor that was tied to a relay connected to the fuel pump. I'll attach a diagram I made and the relevant photos. The relay also looks a little bloated and has corrosion seeping out so may also be going bad.

Going to ditch this setup, remove the relay and wire a new fuel pump directly to the fuse box to turn on in accessory as well as revert the oil sensor to stock. Is this a sound approach? Or is there a best practice for powering fuel pumps. Also, I am guessing this fuel pump might be seeping due to it being a higher PSI range than the regulator and the back pressure is giving it trouble. Any recommendations for low PSI pumps?

& as far as the single connector goes on the stock sensor, where does it attach to on the cluster? One of the screws/posts or should the OEM connectors at the cluster have a wire allocated for this that I should connect to? Having trouble finding it in a wiring diagram.

https://imgur.com/a/1jlMa55

[SubGothius]

A bit odd to have the relay at the pump like that; more typically it'd be underhood near the battery, so most of the wiring would be there where it's easy to access, leaving only a single power wire going to the pump.

It's a good idea to have a relay powering the pump directly from the battery (+) terminal. Powering the pump directly from any other key-on power source may not be able to supply sufficient current and/or may stress a stock circuit that wasn't designed to handle that kind of load. With a relay, the stock key-on power source just triggers the relay with a trivial microcurrent, and then the relay switches power from the battery to the pump.

That PO may have wired key-on trigger power to the relay thru that oil-pressure switch as a safety measure, to cut power to the pump in case of a crash that may sever a fuel line, to avoid hosing down the scene of the crash with raw fuel. Another way of doing this would be with an inertia switch, then you could revert the oil-pressure switch/sender setup back to stock.

I really like the Carter P90091 electric pump for Weber carbs, perfect native PSI with smooth, continuous flow (vs. the pulsing flow of a mechanical or solenoid-driven electric pump), so no need for a regulator.

[85Ram50]

I had that 3 pin oil sensor set up. It was less than reliable. That "another relay?" thing is in fact a self resetting breaker. You can get them at Auto Zone for different amperages. Bussman makes them among others. There are videos of how they work on YT.
I ended up going with a kit I got on ebay similar to this. https://www.youtube.com/watch?v=8GjvRdssvFI
There is also a safety switch to automatically shut it off in an accident that I have not yet bought to put into the circuit.

[smr1618]

Ill keep this set up then and omit the oil pressure sensor safety I suppose and replace it with a switch. PO had a kill switch in the cabin not connected to anything anyways. Appreciate the help, do either of you know where the stock oil sensor ties into the harness or gauge on the cluster?

That pump is nice, I'm hoping to swap this engine sometime soon so don't want to invest more than I need to to get it running well though. Went with a cheap one that is a more appropriate PSI for the weber.

[85Ram50]

Mine is 1st gen. There is a plug hanging down there next to where the OE sensor screws in. The light has been on since I added the nipple and a Tee to install that 3 prong thing as a fuel cut off safety,
The safety switch I am talking about getting one of these days is an Inertia Switch.