73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Interior & Equipment => Instrumentation => Topic started by: darmentle on December 11, 2013, 10:05:00 am
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So i have been reading threw the forums to see if my issue is a bad sending unit in the tank . But from what i read no one is having there gauge needle go blow empty. So i am trying to figure out if its a bad ground or if the gauge is broken. The needle never moves.
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Do you have one tank or two? If two, is the gauge inop with both tanks?
Very often, an inop gauge is caused by the loss of elect. signal at the sender, which is located in the tank. It can also be caused by a stuck sending unit arm.
Better troubleshooting has been described by some of the more knowledgeable guys on the forum- here's a good link to help you-
http://forum.73-87chevytrucks.com/smforum/index.php?topic=24127.msg201708;topicseen#msg201708
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Reading below empty cannot be the sender. One of the supply leads to the gauge is not connected. I think no connect on the +12 will do that.
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dual tanks the passenger side tank i don't use its messed up . I only use the driver side. I am trying to get around having to pull the tank because my truck is on a 6"lift with 37 tires i don't really have the tools to support the tank when i am unbolting it.
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Just measure to the ground and make a plywood box for it to sit on..
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cool if i need to pull the tank i will built a little wood table thanks for the idea. Rich i will hit the connection that the fuel gauge plugs into with a test lite and see if i got power there.
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If you have the panel open and the gauge out, measure across terminals B and C in Photo C on this page. Note that B will be on your LEFT when looking forward into the instrument basket. Measure from there to the center (lower) terminal. You should have 12 volts with the ignition on. The break can also be that the gauge posts are not making good contact in the spring clips due to oxide, but that's less likely.
http://www.chevyclassicsclub.com/the-gm-fuel-gauge-mystery-1965-newer/
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ok i will give it a try
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Ok so i am get 12Volts there. I physically moved the the gauge needle to full and then turn the key and it moved back down to where it was at and stopped.
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And terminal B was +12 with respect to C, right? Not backwards?
Does your gauge have the resistor on the back? See photo B in the link above. The resistor is the little ceramic doodad between terminals A and B.
With the meter on "ohms", measure between terminals A and C in photo C in the link above. This is the terminal on the right when looking forward, and the terminal in the middle (lower).
Note the troubleshooting chart says the cause of needle below "Empty" is a break in the ground between the gauge and the chassis, so it's time to talk about grounds.
Do you have a ground wire in each of the following locations:
- between the battery and the alternator bracket?
- between the battery and the radiator support upper crossmember?
- between the passenger side rear head of the engine and the firewall?
- between the driver side front head of the engine and the right-hand-side frame rail at the steering box?
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I studied a circuit diagram of the fuel gauge internal wiring for a moment and it seems that for the gauge to pin below Empty would require an open or very high resistance ground path, or a broken wire filament inside the gauge. That notion seems to be in agreement with the link that Rich posted.
Use your test light connected to B+ to probe the "ground clip" of the gauge. Any ground issue, under the circumstances you're experiencing, is probably restricted to the instrument cluster or the cluster ground connection to the dash sheetmetal. Bear in mind, there are multiple junctions in the gauge ground path within the dash: the gauge pins-to-clips, clips-to-copper foil, copper foil-to-harness connector ground wire, harness ground wire-to-cab sheetmetal. Unwanted resistance in the gauge ground path can be cumulative among all of those connections. Focus on the connections between the gauge pins, the silver clips, and the copper foil of the PC board (PCB).
Dust and tarnish accumulation in the PCB connections is so commonplace that gently burnishing the copper foil and 'gauge clips,' and perhaps retensioning the clips, may resolve your gauge issue. Read the 7th entry of the Diagnostic and Repair Notes at the bottom of the page in Functional Tests of Factory GM Electric Gauges (http://forum.73-87chevytrucks.com/smforum/index.php?topic=25339.msg211241#msg211241) for more detail on servicing gauge connections.
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Rich yes i was doing it the correct way and i had a ground problem in the pass with the truck not wanting to start so i went threw and replaced most of the grounds on the truck. I did not see a diode on the back of the gauge just 3 little studs. I will finish up the other test later today thanks.
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It's not a diode, it's a resistor. The gauge works by comparing this resistor to the sender unit resistor.
This one will work.
http://www.classicmuscle.com/p-6237-fuel-gauge-resistor.aspx
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is that what i need to order to make it work?
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You may have another problem as well, but it will never work without the resistor in place.
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ok so that is a factory part then that goes there. I will look around today see if i can scrounge one up. if i dont find one today i will order it.
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It was the same resistor used on just about every GM car fuel gauge from 1965 though 1997.
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ok i have 75 Chevy here at work the only one is yard i am gonna walk out there later when i get off and check see if that one has one.
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Why don't ya just get the whole gauge?
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because it had had the OEM fuel gauge and then the person mounted a aftermarket fuel gauge in there to . So i dont know if that fuel gauge is bad or not . ill check it out.
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No luck with the resistor . i even hooked up a ground wire to the ground post on gauge and plugged it in even with a good ground still nothing. i noticed that there is one big plug going into the gauge cluster where does the ground go from there.
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Well, you need the resistor anyway, because it won't work without it. You bolted it across the back of the gauge like in the picture, yes?
The big plug goes all over the place. What truck do you have (year, model)? The wiring diagrams are here, but they depend on the year.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=11766.0
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yea i hooked it up to the correct posts
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yea i hooked it up to the correct posts
Just checking. We have people of all abilities and experiences (or lack thereof) on this forum.
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ok so with having dual tanks and i am only using the driver side tank passenger side is inop. My question is how does the fuel gauge know which tank to read from? The switch on the dash i noticed the previous owner cut the wires off at the switch so you cant use the other side.
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ok so with having dual tanks and i am only using the driver side tank passenger side is inop. My question is how does the fuel gauge know which tank to read from? The switch on the dash i noticed the previous owner cut the wires off at the switch so you cant use the other side.
no. the gauge reads it directly from the selector valve which passes the signal through from the sender. this is shown above the word "RIGHT" where the fuel tank selector valve is represented in the diagram. NOTE: In the selector valve, the components can fail separately. the "mechanical" switch can still operate and actually switch between tanks but the "electrical" signal switch can fail... and vice versa. So what I mean is that the electrical part could have failed on yours but it could possibly still be switching and the gauge won't show it.
(http://i6.photobucket.com/albums/y228/Sabaka454/control.gif)
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That's correct. The tank selector valve is actually two devices on one solenoid/motor: one mechanically selects which fuel tank fuel line (and return) to connect to the fuel pump supply line (and return), the other electrically selects which fuel tank sender wire to connect to the fuel gauge wire.
The mechanical valve can fail, not switching the fuel tank fuel line, even though the electrical switch works; the electrical switch can fail, not connecting the gauge wire to the correct sender wire, even though the fuel valve works; or the solenoid can fail (most common), so that neither the mechanical fuel tank selector valve nor the electrical fuel tank sender switch works.
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I don't know what the issue going on the fuel selector . He had cut the wires going to switch at the dash and said just use the driver side only. Its not big deal to me not having both tanks i just want the gauge to work. Ill probably have to get under there tomorrow and just start hooking the wires back up that he cut and see what happens. I bet that is what the issue is with the gauge is still on the inop tank.
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Technically the cut wires at the dash switch should not affect the gauge reading.
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so i got to work on it today some more got under the truck finally. And noticed the whole fuel valve is gone he has some 3 way device up there with the fuel lines going into it. I also found the wires to the driver side tank pulled the ground wire off it was caked in all sorts of good stuff so i cleaned it up really good and put it back together still the gauge is still doing the same thing. I also notice the wire coming threw the frame for the sending unit is a blue wire not a pink wire it goes all the way up to the junction in the fire wall.
(http://i255.photobucket.com/albums/hh126/neothar/20131214_092115_zps4c69426d.jpg)
(http://i255.photobucket.com/albums/hh126/neothar/20131214_092138_zps1fc09e37.jpg)
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That's a fuel tank selector valve, though not the same as the original, I think.
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_3030229-P_x_x?cm_mmc=ACQ-_-Google-_-GPLA-_-3030229&ci_src=17588969&ci_sku=3030229&ci_gpa=pla&ci_kw=&gclid=CODApMG8sLsCFawRMwodLx4AVA#utm_source=acq&utm_medium=google&utm_campaign=gpla&utm_content=3030229
Here's what I think is the stock one.
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_fuel-tank-selector-valve-acdelco_18051445-p?searchTerm=fuel+selector+valve
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So am about to say oh well and get an aftermarket cheap fuel gauge and see if that works.
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Measure the ohms between the ground terminal on the gauge and the chassis, even better between the ground terminal of the gauge and the ground of the battery. I'm pretty sure the problem is on the ground side of the gauge.
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do you know where the ground wire from the fuel gauge goes like where its bolted to does each gauge have there own ground .
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Depends a bit on the year. What year and model of truck is it?
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73 k20 4x4
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Here's the pointer to all the manuals.
http://forum.73-87chevytrucks.com/smforum/index.php?topic=25639.msg213706#msg213706
From the pointers in that message, here's the wiring manual for your truck.
http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/X_7305_1973_GMC_Truck_Wiring_Manual_CK_10_30_Pgs_Only.pdf
The ground from the instrument cluster is the wire at the lower left of the connector (also lower left as mounted in the truck) labeled 20B-150B. The "B" in "20B" stands for black, so that should be a black wire (BRN is brown, LBL is light blue, DBL is dark blue). As shown, it immediately goes to a 4-wire splice behind the dash. One of those wires, labeled 20B-150A, goes to a sheet metal ground. Find the splice, check it. Find the sheet metal ground, check it.
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I got it working i had to install a aftermarket gauge thanks for your guys help.
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How weird. Broken ground wire inside the gauge maybe? From tests it seemed like the gauge was good.
Anyway, you got it, so that's good. Thanks for letting us know.
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Well there was two issue going on . The ground was fine the first problem was that the wire for the sending unit wasn't sending a signal at the gauge cluster. I tested the the connection at the cluster and i was getting no ohms there. So i followed my sending wire to the out side junction at the fire wall and tested it 84 ohms i had little less then a full tank so it was correct. So i ran a jumper wire from the wire at the junction to my OEM fuel gauge and it was still having a problem. So i just hooked up the aftermarket gauge.
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By aftermarket gauge, was it a direct replacement gauge for the OEM?
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that fuel selector is correct for your year. Well you narrowed the problem down to inside the dash. how did you wire up the aftermarket? you obviously had to go outside the cab or else is should not have worked either if you spliced into it in the dash.
well if your jumper wire didn't work then it is the gauge.
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i just bought a cheap aftermarket gauge little 2" one from orielys for now. i was getting signal on the inside the cab at the fire wall so i ran the wire there. for now i am gonna run like that until i can find a working OEM in gauge then i will pull out the whole gauge cluster and fix it right.
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http://www.classicparts.com/Gauges-Switches/products/1012/
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Sweet thanks again 50 Bucks for a fuel gauge is good deal and knowing that its working is a even better
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I put a second gauge in the empty position on my cluster, for the other tank. I got it from them, and no problems.