FJ60 oil pressure gauge fried - how to fix? (2 Viewers)

[kenavt]

Hey folks, I'm afraid I fried my oil pressure gauge by attaching my oil pressure sender wire to the wrong post as part of my engine swap. It was pinned high when I had it on the wrong post (presumably because I had grounded it by putting it on the wrong post), now it's always low.

Has anyone successfully repaired their oil pressure gauge - replaced whichever component was fried? I have pulled the cluster from my car, about to tear it apart, was hoping maybe someone had figured it out before.

 

[HemiAlex]

I would just look for a new cluster or find a part out. Far easier than repairing and troubleshooting.

You should be able to find a cluster for $200 ish. The gauge is long NLA.

 

[CruiserTrash]

Hey folks, I'm afraid I fried my oil pressure gauge by attaching my oil pressure sender wire to the wrong post as part of my engine swap. It was pinned high when I had it on the wrong post (presumably because I had grounded it by putting it on the wrong post), now it's always low.

Has anyone successfully repaired their oil pressure gauge - replaced whichever component was fried? I have pulled the cluster from my car, about to tear it apart, was hoping maybe someone had figured it out before.

View attachment 2952580

View attachment 2952579

I have a cluster I'd sell, but you're not gonna like the mileage haha. You could always swap just the components on that side though. Sorry, not gonna split it up - I'd be stuck with the rest of it forever.

 

[Spike Strip]

There was a thread (searching didn't immediately locate it) where someone tried but was unable. It burns it up pretty bad. Good used are available.

Now may be your chance to install an electrical or mechanical Oil Pressure gauge that will be far more accurate anyway.

 

[kenavt]

I went ahead and took it apart to find the short or damage, and... found some interesting things, but unfortunately no solution. Firstly, it disassembles pretty easy with a Philips #1, #0, and a 7mm, and the gauge cluster falls apart into four different segments, so you can swap each one apart individually.

I was expecting to see a lot more electronics, but there's just the one thick printed circuit board on the back that just distributes the wiring (and adds a secret capacitor).

I was shocked to see that three of the gauges are magnetically driven. Running a specific current through the coils (controlled by the oil pressure sender/coolant temp sender/fuel sender). The fourth (voltmeter) probably is too from the coils but transformers aren't my thing, and I didn't want to tear it down more.

The coolant temp gauge and oil temp gauge look identical. There's just this stamp on the side (date?) that's the only difference. Without checking the number of turns on the coil, seems to me like they'd be interchangeable other then that the markings on the dials are different, of course.

 

[CruiserTrash]

I went ahead and took it apart to find the short or damage, and... found some interesting things, but unfortunately no solution. Firstly, it disassembles pretty easy with a Philips #1, #0, and a 7mm, and the gauge cluster falls apart into four different segments, so you can swap each one apart individually.

View attachment 2953286

I was expecting to see a lot more electronics, but there's just the one thick printed circuit board on the back that just distributes the wiring (and adds a secret capacitor).

View attachment 2953287

I was shocked to see that three of the gauges are magnetically driven. Running a specific current through the coils (controlled by the oil pressure sender/coolant temp sender/fuel sender). The fourth (voltmeter) probably is too from the coils but transformers aren't my thing, and I didn't want to tear it down more.

View attachment 2953302

The coolant temp gauge and oil temp gauge look identical. There's just this stamp on the side (date?) that's the only difference. Without checking the number of turns on the coil, seems to me like they'd be interchangeable other then that the markings on the dials are different, of course.

View attachment 2953299

View attachment 2953298

There’s probably an FSM test procedure on the sender. I’d also check resistance on the wiring.

 

[kenavt]

So as for the condition of the oil pressure gauge... the FSM says to measure resistance across the terminals and you should get 55 ohms (same resistance as for the fuel sender and coolant temp). I was measuring 45 ohms at DC, so... something has changed. But if something had shorted or fried I would have expected it to be much more radically different, in the single digits. If resistance had only changed that small amount, based on looking at coolant temp resistances that can go up to 200+ ohms... I would only expect the oil pressure gauge to have a different response to the sender (not play dead).

Next was looking at the gauge itself. Two things stick out: one, the dial is much, much more resistant to being pushed than the other gauges (it snaps back immediately, whereas the others do more of a float). The second is that the wire has somehow melted the plastic and buried itself inside. I can't imagine how much heat would be needed to burrow in that deeply, I couldn't budge it at all with light pressure from tweezers.

Otherwise there aren't signs of. I was puzzled, staring it over, and about to put it back together and write everything off when I realized: the bar the coil is on had heat discoloration at the corner and possibly under the coil. It was also bent substantially out of alignment versus the coolant gauge, pushing the dial way, way back. I think it must have deformed under the (constant... since it took me months to realize I was shorting this...) heat and curled in itself. This would explain why the oil pressure dial is so much more resistant to being turned by hand.

First one is the coolant gauge, second is the (broken) oil pressure gauge.

Close-up side-by-side:

So I think if there was a solution, it would be in two parts somehow...

• Straighten out this metal piece - re-bend it back to position. And hope that the stiffness hasn't changed.
• Somehow bump the resistance back up to 55 ohms in the system, up from 45... so the voltage drops are correct. Otherwise presumably the mapping of oil pressure sender resistance to coil resistance is off and the dial response is wrong. That's assuming the coil is still functioning properly and hasn't shorted inside itself. Big if. I can't imagine rewinding the coil... would have to drill the rivets out to pull it apart further, it would be a tedious job

Either of these actually taking seems pretty unlikely. I think I'll try to straighten it out since I've taken it this far apart, and see if that works, but keep my eye out for a cheap working replacement in the long term.

 

[kenavt]

There’s probably an FSM test procedure on the sender. I’d also check resistance on the wiring.

This is why I should write my posts faster.

The FSM also mentions testing the gauage with a 3.4W bulb... unclear to me what that bulb is, or what that accomplishes. For the sender it seems like a more useful test, or you could measure the resistance against battery positive (12V).

 

[CruiserTrash]

Great stuff. I’d also be thinking of why that wire got hot and buried itself in the plastic!

 

[kenavt]

After having tried to straighten out the metal piece, I reinstalled the cluster in the truck. The needle now rests right by the bottom of the gauge (probably not where it's supposed to rest, I would guess). When starting the truck, it rises up above the 1/3rd mark, and after driving for a bit, will hit a max of 2/3rds (at least from my 20-minute driving trip yesterday).

So I wouldn't trust the accuracy of this gauge at all since the resistance is now 45 ohms instead of 55 ohms, but it does seem to be vaguely responsive. Having a binary response of "yes oil pressure" or "no oil pressure" is much better then I've ever gotten from this gauge in my ownership of this truck, so I'm pretty happy with that!

If I wanted to try and save this gauge and fully make it accurate, the thing to do would be to map the oil pressure sender resistance at various pressures versus the gauge's response, like the very cool Temperature Gauge Calibration - How To. Then put some sort of sticker or note over the gauge with that mapping. But that is way more work then I'm willing to put into this. Here's to having another vague data point on how well the truck is running.

 

[BluewaltFJ60]

just dealing with this very same issue, Got my truck back with a new engine (rebuilt), guy says, oh the oil gauge is not working....and it is not the sender. I don't have the melted wire like you do and my FSM says 65 ohms resistance for my FJ60, I am getting 45. Would love to be able to fix this thing

 

[deaven]

I just repaired my gauge after shorting to ground just like many on this thread. I was able to repair it, and also in the process I obtained a working used gauge and calibrated the current vs reading (see attached). At 100mA, the needle should be just above the boundary between normal and high range as shown. You can adjust by carefully removing the red needle, and gently bending the tang that the needle attaches to with a pair of needle nose pliers. (As others have noted, shorting out causes it to max out and bend itself the wrong way.) The needle itself just sits on the tang and has a small plastic press-fit retainer.

Hope this helps others, I have benefited from this and other threads on the topic.

My repaired gauge is working perfectly now. While it wasn't, I had a mechanical gauge attached since I had just rebuilt the engine and so had a keen interest in pressure; it seems the deflection shown in my picture would correspond to a pressure in excess of 55psi, about the same as the bypass on a properly functioning oil pump.

 

[TheEngineer]

After having tried to straighten out the metal piece, I reinstalled the cluster in the truck. The needle now rests right by the bottom of the gauge (probably not where it's supposed to rest, I would guess). When starting the truck, it rises up above the 1/3rd mark, and after driving for a bit, will hit a max of 2/3rds (at least from my 20-minute driving trip yesterday).

View attachment 2960669 View attachment 2960670

So I wouldn't trust the accuracy of this gauge at all since the resistance is now 45 ohms instead of 55 ohms, but it does seem to be vaguely responsive. Having a binary response of "yes oil pressure" or "no oil pressure" is much better then I've ever gotten from this gauge in my ownership of this truck, so I'm pretty happy with that!

If I wanted to try and save this gauge and fully make it accurate, the thing to do would be to map the oil pressure sender resistance at various pressures versus the gauge's response, like the very cool Temperature Gauge Calibration - How To. Then put some sort of sticker or note over the gauge with that mapping. But that is way more work then I'm willing to put into this. Here's to having another vague data point on how well the truck is running.

This may have saved me some time/money. The wire from the pressure sending unit fell off while I was driving and I thought I suddenly lost oil pressure. Reconnected the wire incorrectly, while it was running and now my needle rests below the L on the gauge. But if I can take it out and bend the metal bar into place it should return to normal. If it's any consolation mine used to rest at the bottom of the gauge when it was "working" like yours does now.

 

[onemanarmy]

I just repaired my gauge after shorting to ground just like many on this thread. I was able to repair it, and also in the process I obtained a working used gauge and calibrated the current vs reading (see attached). At 100mA, the needle should be just above the boundary between normal and high range as shown. You can adjust by carefully removing the red needle, and gently bending the tang that the needle attaches to with a pair of needle nose pliers. (As others have noted, shorting out causes it to max out and bend itself the wrong way.) The needle itself just sits on the tang and has a small plastic press-fit retainer.

Hope this helps others, I have benefited from this and other threads on the topic.

My repaired gauge is working perfectly now. While it wasn't, I had a mechanical gauge attached since I had just rebuilt the engine and so had a keen interest in pressure; it seems the deflection shown in my picture would correspond to a pressure in excess of 55psi, about the same as the bypass on a properly functioning oil pump.

View attachment 3419394

how did you repair it? the same procedure above.....bending the bar back straight?

or are there other 'fixes'?

 

[ToyotaMatt]

if your yellow wire w/ black tracer stripe shorted to ground it roasted it and the blue circuit board too