[fj40z]

So on the way home today I was stopped at a light when I glanced down at my oil pressure and noticed it was maxed out, needle all the way to the top. While I was stopped at the light I cut the truck off and the needle never dropped, luckily I was literally less than a 1/4 mile from my house. As I pulled into the driveway I put it in park got out and checked under the hood. I took off the oil filler cap and the engine idled way down,almost dying just for a second then went back to normal. I checked the gauge and it had went down a little. I let the truck cool down then checked the oil, it was about a quart low. I pulled the PCV (which was replaced this past winter) and it rattles so Im assuming it is OK. So I started it back up and drove it around for about 25 minutes and everything seems to be normal. Any idea what would cause this? Im clueless.

[concretejungle]

bump.

bump.

[john_eckels]

I would start with the cheap options like replacing the oil filter. I am not sure if a plugged filter would cause this or not though. I would also pull the wire off the sending unit and clean the contacts. After that maybe replace the sending unit. The fact that you cut the engine and the pressure was still high says that something may be plugged or the gauge is faulty

[concretejungle]

i was caught off guard by the fact that he pulled the oil cap off and the truck stumbled and almost died.

[Lka1988]

Originally Posted by concretejungle

i was caught off guard by the fact that he pulled the oil cap off and the truck stumbled and almost died.

Loss of vaccuum (I think). The OP has a pre-OBDII truck.

Post OBDII trucks can compensate and adjust, and won't stumble.

[-Spike-]

Oddly enough, I had this very same thing happen to me this weekend, on the way to a trail... I would have been a lot more concerned if it had gone to the bottom. After conversing with Tools R Us about it a little (and checking the oil, which was fine) we concluded that the sender was probably going or gone. It started reading correctly a bit later, and hasn't gliched since in two days of wheeling and highway use. I wouldn't sweat it, if it goes permanent you might look at the sender or the connector. Our thinking was that the wire would have to short to ground or the sender itself might have a short in it. Because it wasn't doing it intermittently, I don't think my problem is a wire. If it were I'd expect the needle to go up and down constantly or stay up.

-Spike

[treerootCO]

A plugged filter goes into bypass and just doesn't filter the oil. Even good filters don't filter oil unless you are at idle. Spun bearing would cause the pressure to spike. Only way to confirm is to drive it until it seizes or hook up a mechanical gauge for a 2nd opinion.

[concretejungle]

Originally Posted by treerootCO

A plugged filter goes into bypass and just doesn't filter the oil. Even good filters don't filter oil unless you are at idle. Spun bearing would cause the pressure to spike. Only way to confirm is to drive it until it seizes or hook up a mechanical gauge for a 2nd opinion.

haha, mike, that's kinda funny. I would have said something similar....."just drive it until it breaks, then fix it"....

Steve, maybe Eric has a mechanical pressure gauge we can hook up to measure your pressure? Also, do a full oil/filter change and see what happens. IMHO

[fj40z]

So I drive the 80 to work today, maybe 10 minutes, no problems. I leave work around 1:00 to go to class, drive about 30 minutes no problems. Leave school to drive home around 4:00, drive about 30 minutes, stop at the same light as yesterday and glance at the oil pressure gauge and I cant believe my eyes it is starting to climb, at the same time the light turns green and as I accelerate it maxes out and stays maxed out until I get home and cut the truck off and then it slowly fades down. I swear I nearly crapped my pants. Does the fact that this is happened 2 days in a row at the same place darken the prognosis?

[jonheld]

Originally Posted by fj40z

I get home and cut the truck off and then it slowly fades down.

Bad sender unit or possibly an electrical issue would be my guess.

[Cruiser Jimmy]

X2 on the oil sending unit.

[IdahoDoug]

There is one other unlikely possibility. There is an oil pressure relief valve in the block that uses a simple spring that is pushing against oil pressure. When it gets too high (high rpm cold oil, etc), this valve opens to compensate. It's a cinch to replace and Cdan has them in stock (I have 3 of them from a year ago). I think it would take about 5 minutes as it's a single screw holding it in and it comes straight out of the block.

However, FIRST THING I'd do IMMEDIATELY is change the oil and filter even if it's only a week old. May have a defective filter or you'll discover shavings in the oil, etc. First thing. Would not even drive it until I was sure the engine was getting fresh oil - then I'd work on sender, etc.

DougM

[concretejungle]

Good points Doug. I agree. (from an armchair quarterback)

[turbocruiser]

Originally Posted by treerootCO

Even good filters don't filter oil unless you are at idle.

Wow I just did a double take on that one. I've never heard or read about this but is that true that the filter isn't filtering unless you are at idle or am I reading that wrong?

[Tools R Us]

Originally Posted by fj40z

So on the way home today I was stopped at a light when I glanced down at my oil pressure and noticed it was maxed out, needle all the way to the top. While I was stopped at the light I cut the truck off and the needle never dropped, luckily I was literally less than a 1/4 mile from my house. ...

I have never seen this failure be anything but electrical. If the motor is off, key is on, the oil pump isn't pumping any oil and the gauge is reading at the top, there is a short to ground in the sensor side of the circuit. The next test is to make the same thing happen and unplug the sensor wire, if the gauge falls it's a bad sensor or insulation failure close to it, if not continue testing the wiring back to the gauge, then test the gauge. Changing the oil would be a waste of $$$.

The gauge gets power from the gauge fuse, ground comes from the sensor, open = gauge at the bottom, grounded = gauge at the top. Yours is intermittently grounding, it could be a bad sensor, wire insulation failure shorting to ground or a bad gauge.

[Squash]

If not the sender or wiring it could be a resistor in the gauge...
Buy or borrow a mechanical gauge.

Unsrew your sender which is easily reached from under the passenger side and install the mechanical gauge.

Otherwise the FSM has some ideas.

I use both systems.

[fj40z]

Guys, Thanks a bunch for the input, when I brought the thread back up just now and read that the general concensus is that it is nothing major it was a BIG relief. Tomorrow evening Im going to try get in there and see what I can find...........you know I didnt think about it until now but about 2 weeks ago the cd player just went out, totally dead, wouldnt turn on or anything, so I shut it off for a few minutes started it back up and it worked fine. Then I noticed before last weekends wheeling trip the fm modulator I had circuit chity install for my mp3 player doesnt work anymore. Could there have been a short or something that would have affected them both?

[IdahoDoug]

Ahhh, the plot thickens. Listen to Mr. Patterson on this one. Bet Circuit City electricians disturbed something that is only now coming home to roost.

DougM

[Brian894X4]

This is 99% definately the wire from the sender to gauge is grounding. I've had this exact same thing happen to me on a Toyota minitruck. Since the gauge works part of the time, the wire is probably not disconnected from the sending unit, which is the most common cause. So, most likely the oil pressure sending wire has a chaff in it somewhere and is grounding out intermittently, depending on where the wire happens to rub. It's possible the wire is just barely disconnected and is bouncing between the sensor body which is fully grounded and the sensor connector, giving you the different readings.

The Toyota oil pressure gauge measures current based on how much resistence the sending unit has to ground. The gauge is never supposed to fully grounded or it will be destroyed. A fully ground gauge wire will cause the gauge needle to max out.

Once the gauge is destroyed (wire mechanism inside is bent), eventually, it will cease to read above zero or just above zero.

Before I replaced the sender, I'd carefully look at the wire. I don't think these senders go bad very often, but a wire can easily get chaffed. Plus a new sender is spendy.

The other problem is now that the gauge has been maxed out, it's likely out of calibration anyway, so it's pretty much useless as far as reliability, unless you got lucky.

[fj40z]

So does everybody think it would be wise to hook up a mechanical gauge along with the factory or just try to fix the factory or only run the mechanical? If so is there an extra place designated on the block for hooking it up or does it have to go where the factory gauge connects ( I apologize in advance if these questions sound amazingly stupid) I've never hooked up any gauges up before and I just dont want to screw anything up.

[Tools R Us]

Originally Posted by fj40z

So does everybody think it would be wise to hook up a mechanical gauge along with the factory or just try to fix the factory or only run the mechanical? If so is there an extra place designated on the block for hooking it up or does it have to go where the factory gauge connects ( I apologize in advance if these questions sound amazingly stupid) I've never hooked up any gauges up before and I just dont want to screw anything up.

My first move would be to find the problem, then decide on the fix. It maybe as simple as putting some tape on a wire?

[-Spike-]

Originally Posted by Tools R Us

My first move would be to find the problem, then decide on the fix. It maybe as simple as putting some tape on a wire?

x2. As far as the guage being damaged goes, I had it max out twice, then work normally. Calibration is not an issue, as the guage is relative anyway. If it reads pressure anything like it did before, it's fine. Find your problem before you start adding guages.

-Spike

[fj40z]

Originally Posted by Tools R Us

My first move would be to find the problem, then decide on the fix. It maybe as simple as putting some tape on a wire?

Good point, I tend to get a little ahead of myself. I spent some time looking at what I believe is the sending unit, round thing about halfway down the block on the passenger side more to the front of the block, so far everything looks good around the sending unit. I ran out of light before I could get into the dash and check where circuit city did the stereo work. Also a good point on it not being a big deal if the gauge is out of calibration a little bit since its not showing a psi reading anyway.

[concretejungle]

steve, come by and get my FSM.

[Tool Pusher]

When mine maxed out I replaced the sending unit. Fixed the problem.

David Sword

[fj40z]

Originally Posted by concretejungle

steve, come by and get my FSM.

Thanks Alex, I might try and pick it up later if thats alright.

[Brian894X4]

Originally Posted by -Spike-

x2. As far as the guage being damaged goes, I had it max out twice, then work normally. Calibration is not an issue, as the guage is relative anyway. If it reads pressure anything like it did before, it's fine. Find your problem before you start adding guages.

-Spike

The calibration issue is that the needle is held against the stop, while the mechanism inside is still trying to push the needle which then bends the mechanism out of calibration. The good news is that the needle will read lower pressure than actual pressure instead of the other way around. The bad news is that if really bad, the needle will be stuck on zero. The guages in the FZJ80 might be stronger than the ones in the Toyota mini-trucks. Those gauges get destroyed on the first max out. Very, very delicate inside. The LC ones are a newer design and might be more heavy duty.

[fj40z]

I hope that is the case, I have a feeling that if there is a short its where circuit city did the stereo work back a few months ago, because the wire looks good from the sending unit. There is a very reputible stereo shop here in Greensboro that I talked to you yesterday evening and they said that they could pull out all the crap circuit city put in there and put in a new stereo that I could plug my mp3 player in directly without the fm modulator for a very reasonable price and hopefully fixing the short in the same process.

[jfz80]

If that doesnt work check your remote start harness.... i believe its in the steering column.

[fj40z]

I know it sounds crazy but I believe replacing the radio fixed it. I had it replaced Sat. morning and I've driven all 3 days since and hasnt done it since, although the pressure registers a little lower at idle, possibly the gauge is out of calibration from being maxed out twice. The stereo shop that pulled out the mess circuit city had put in there said it was really cobbled up. Hopefully this is the permanent fix Im looking for, if nothing else I got the stereo upgraded and got rid of a definite short in the dash. The new stereo is a huge improvement over the previous one. Heres a pic.