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post #1 of (permalink) Old 09-27-2006, 08:26 PM Thread Starter
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fluctuating oil press gauge

again i know this is a jeep board but this group is 100x more responsive than the toyota group and this question is pretty generic.

my dad's 76 toyota fj40, he came home today and said that his oil gauge was fluctuating severely. and he could control how it moved by accelerating.

i searched the forum but no much to go on and no idea how to diagnose this other than start with the small things like sending unit. and hope its not the pump or bad bearings.

any tips would be great. thanks.
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post #2 of (permalink) Old 09-27-2006, 09:03 PM
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Re: fluctuating oil press gauge

Here is what I know...and yes it isnt very much [img]/ubbthreads/images/graemlins/grin.gif[/img] My CJ's oil pressure gauge went bad, replaced it with an other electric gauge, and it wouldnt read more than 5psi (previous gauge read much better). Returned that gauge and replaced it with a michanical one Oil pressure "op" about 30psi. Changed oil and the psi dropped to 20 at idle and as I accelerate the "op" climbs back to the 30psi range. When I asked about it I was told that it is normal. The older oil was dirty and created more resistance thus a higher "OP" also the filter may have had a little bit of a clog thus a higher "op" reading.
check your oil first! then check your gauge & make sure it is the correct sending unit for the gauge (if you havent changed it, or you changed it with one that came with the cauge it should be ok). The gauge may be going bad. Change the oil maby the filter is clogged. Other than that Im not sure.
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post #3 of (permalink) Old 09-27-2006, 10:12 PM
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Re: fluctuating oil press gauge

After you have tried the sending unit issues, the nexed step would be the oil pump system. I do not know about Toyota, the AMC V8s have problems with the housing around the pump gears wearing causing low oil pressure.

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post #4 of (permalink) Old 09-28-2006, 11:37 AM
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Re: fluctuating oil press gauge

The fact that the pressure can be controlled by the accelerator bothers me.

If the gauge or sending unit went bad, accelerating would not affect it - or shouldn't. How/why would the gauge even know to change if the pressure didn't?

Could be a number of things - oil diluted with fuel? - change it - smell it - mechanical fuel pump going bad? Injector leaking badly? Fuel pressure regulator leaking fuel into the vacuum line then into the crankcase?
Low oil level? Badly sludged oil?

Could even be a bad ground - the rocking of the engine changes the ground, thus the reading? Turn the lights on and off? Gauge moves? = Body to engine Ground.

CVR? Constant Voltage Regulator - in the dash - keeps the voltages to the instrument panel consistant, so changes in charging system voltage don't affect the instruments. When the CVR goes bad, the gauges go up and down with RPM's. Check to see if you even have one, some don't. It's a cheap item - usually they plug in.

Let us know.
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post #5 of (permalink) Old 09-28-2006, 05:39 PM Thread Starter
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Re: fluctuating oil press gauge

changed the oil this afternoon. started it up, no pressure. wiggled the wire on sending unit and the gauge started to read. not sure if this was due to pressure building up after oil change or the wire.
but now at idle the gauge is steady in the middle, and reads just under H or high while driving. it isnt fluctuating anymore but it used to be a consistent reading at just under H.

has an electrical fuel pump.
tomorrow ill check grounds and CVR. is there a seperate cvr for every gauge? the oil pressure gauge is the only one fluctuating.
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post #6 of (permalink) Old 09-28-2006, 07:08 PM
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Re: fluctuating oil press gauge

Only one CVR - but about the only thing commonly used on it is the oil pressure gauge.
You could check it - get to the back of the oil gauge - one terminal comes from the CVR - put a voltmeter on there to monitor the voltage. If it fluctuates with the oil gauge - replace CVR.
And - put that voltmeter on the other side of the meter - that's coming from the sensor. If it's doing the fluctuating, it's the wiring or sensor.

Next - unplug the sensor at the sensor - use an Ohmmeter to monitor the resistance - if it's fluctuating, try a new sensor or try a mechanical gauge right in the hole where the sensor is. Hopefully it's not doing the fluctuating there. Then it's inside the engine.

Another indication - the fluctuations themselves - watch them.
An electrical issue the gauge usually "jumps" quickly up and down - real fast, as fast as the meter can move.

A real oil pressure issue the gauge moves up and down as the oil pressure changes, you'd say it's quick, but not really "jumping."
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