Fuel and Temp gauges intermittent (1 Viewer)

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A

adavis

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Feb 27, 2013
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Oakesdale WA
After bringing my FJ back from its 10+ year slumber I have found all the gauges work, but the fuel and temp gauges fluctuate. They come and go in unison and randomly. It only affects the temp and fuel gauges.....the oil and amp gauges never have issues. I'm guessing its a ground issue but does anyone have a suggestion on where to look first? I've done some searching but can't find anything regarding this exact issue. Is there a certain location that would only affect those two gauges? I've wiggled wires under the dash it hopes that I would catch something but nothing yet. They just randomly work and stop working as I'm driving down the road.

Any help or advice would be greatly appreciated. Thanks.
 
I've had a similar issue with gauges.. it turned out to be light corrosion on the fuse holders, and the chrome part of the barrel fuses. I rolled up a bit of sandpaper and scuffed up the brass holders and replaced the fuses. On the HJ47 I think they run through the Heater fuse, it maybe different on yours.
 
Thanks @duncanrm. I originally didn't have headlights (but all other lights) so I took a round file and cleaned every fuse holder in the block. It fixed the headlight issue right away. I will check again with the fuse to the gauge panel, but I thought it was odd that only those two specific gauges are having an issue. Thanks for the suggestion.
 
As said, check fuse contact condition. Then go through and check and clean the grounds. I had this similar problem on a 79 I was working on and it was a corroded ground between engine and frame (starter to frame).
 
I completely understand the importance of grounds, but the weird thing to me is that ONLY the fuel and temp gauge....nothing else. All dash lights work. I just thought maybe there was a specific wire that would ONLY affect those two gauges. I had my fingers AND toes crossed..... :)
 
What year 40?. I think the early 40s had a separate wires going to the gauges. Later versions I think have a printed circuit board on thr back and a barrel connector/plug. Disconnect the batt b4 removing the gauge cluster. It has exposed contacts for the amp gauge.
 
I can't believe it's been 1.5 years since I brought this up. It's still an issue that I'd like to fix. As stated above, on my 1973 FJ40 the fuel and temp gauges work most of the time but will randomly "lose power" and the needles will slowly drop, but then bounce back up like power is restored. It only happens to those two gauges and doesn't affect any lights or the temp or AMP gauge. I've gone over the wiring diagram and I don't see anything standing out that would ONLY effect the temp and fuel gauges.

DISCLAIMER: I'm NOT an auto electrical guy so if I'm missing something stupid please feel free to tell me. I would GUESS that it is a ground issue but any suggestions on where to look that would ONLY effect those two gauges? All other electrical in the vehicle works completely fine with no problems and this doesn't effect the operation of the vehicle other than being able to monitor fuel level and engine temp.
 
Is your gauge cluster a circuit board style with big plug for wires or the older wired type ? If it is the older type I would suspect the power jumpers are loose or bad connections behind gauge cluster, slide it out and follow the power input ( not the ampmeter) and follow it to the gauges, find yer problem.
 
So have you cleaned every contact for the senders and gauges? Disconnect the battery before you pull the dash panel.
 
Thanks for the quick responses.

@peesalot Mine is the older style. I don't recall seeing any type of circuit board behind mine. I'll pull my cluster (after I disconnect the battery @charliemeyer007 ) and try to trace out the power. I hadn't really touched anything behind the cluster yet because I figured I'd probably mess up more than I'd fix (see DISCLAIMER in my last post). If I find the problem I'll post the resolution.
 
I'll just add my 72 fuel gauge has never really worked right since I got the rig in 82. It reads F for a really long time, 1/2 is about correct and so is E as in you are walking. The oil pressure gauge was interment and inaccurate. I tried a new sender, no improvement so I installed a direct read gauge. I used a section of fuel hose from the back of the gauge to the engine side of the fire wall (over the nylon oil line) so I wouldn't get a face full of hot oil if the plastic line broke. Been there since like 85 - still works great.
 
So here's what I'm confused about. It looks like, to me, that the temp and fuel gauges are not connected per this wiring diagram. If any gauges should be affected in unison it would be OIL and FUEL (the pink line). From what I see on the diagram, TEMP and FUEL don't appear to be tied together at the panel, right?

1710451587213.png
 
charliemeyer007 said:
I'll just add my 72 fuel gauge has never really worked right since I got the rig in 82. It reads F for a really long time, 1/2 is about correct and so is E as in you are walking. The oil pressure gauge was interment and inaccurate. I tried a new sender, no improvement so I installed a direct read gauge. I used a section of fuel hose from the back of the gauge to the engine side of the fire wall (over the nylon oil line) so I wouldn't get a face full of hot oil if the plastic line broke. Been there since like 85 - still works great.
Click to expand...
I agree and have a few vehicles that have similar results with the fuel gauge. THIS scenario with my FJ40 is different, in that the fuel gauge works fine showing the correct level of fuel, but if you watch the needle it will randomly start to drop slowly then it will randomly rise back up to the correct level. This corresponds directly with the exact same symptom with my temp gauge. They both do the exact same thing at the exact same time. Just giving more info if it helps at all.
 
Just cause its what I do, when its not working, reach over and wiggle the sender wire under pass seat & see what happens ?
 
Ground

forum.ih8mud.com

Never underestimate the importance of a ground

I drove my truck for the first time in too long. I'd swear I had electrical gremlins if I didn't know the source of the problem. My windshield wipers stop working when I step on the brakes, hit a bump, or turn a corner. The front turn signals also light up when Braking. The hazards also do...
forum.ih8mud.com forum.ih8mud.com
 
@MOTOV8R That's the kind of information I knew someone would have! I'll mess around with the wire to the fuel sending unit and see if I find anything. My fj40 has a second fuel tank that was installed at the dealership when new and that tank has a fuel sending unit too...that works. I flip a switch on the dash to change tanks and the fuel gauge reads accordingly.

Both gauges read accurately about 85% of the time so it's really a minor annoyance. If you watch them the needles will randomly start to slowly drop (in unison) and then after a second or 3 they will bounce back up to the correct reading. I'm sure it's probably a loose connection somewhere so I'll start with the fuel sending units and go from there. The info about the fuel gauge supplying power to the temp gauge gives me a great place to start. Thank you.
 
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