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73-87 Chevy _ GMC Trucks => Interior & Equipment => Instrumentation => Topic started by: jpatters13 on December 07, 2013, 09:16:31 am
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I have an 84 K10 Silverado I recently purchased for my 16 year old daughter. It has dual fuel tanks. I am slowly going throughout he truck and fixing what seems to be broken or not functioning properly. Here's my issue: I have filled both tanks and regardless of which one is selected, the fuel gauge will only read about 2/5 full when the tank is completely full. Then, whenever the selected tank gets near empty, the gauge will begin to come down and function properly. I believe both sending units are original equipment. Should I replace the gauge first or start with the units...or do you have another suggestion? Any advice would be highly appreciated. Thanks!
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It reads 2/5? So are you saying below a certain point it reads normally just won't climb about wherever 2/5 is? Can you pop the wire off of the switching valve and observe the gauge? It should go past full
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It's probably the resistor on the back of the fuel gauge. If they break open or lose contact, you will see that. As VileZambonie says, if you pull the plug off the tank selector valve (on the passenger frame rail in front of the rear tire), then the gauge should go to Full. If not, it's at the gauge, and simplest is to replace the resistor.
This is a pain in the butt to do, because you have to peel the instrument panel back until you get to the instrument basket so you can pull the gauge out. The resistor is bolted across the terminals on the back of the gauge, the gauge just plugs into the basket.
Here's the resistor you need. At least this is the one on my 78; I think 1984 is the same.
http://www.classicmuscle.com/p-6237-fuel-gauge-resistor.aspx
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Yes, the tank reads about 2/5 full and no more regardless of how much more fuel is in the tank. I will start with the plug on the frame rail. I think I know where it is. Do I just pull the three-plug adapter out which should then send zero resistance to the gauge and it should go to full?
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I don't know what you mean by "the three-plug adapter".
You should have a widget like this on the inside of the frame rail in front of the rear tire. Pull the plug off and see what the gauge reads. This will put infinite resistance (not zero) to the gauge and it should go to FULL.
(http://www.oilybits.com/images/uploads/POLLAK%20PLUS%20LOOM%20AND%20SWITCH.jpg)
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Okay, sorry, I meant three-wire. Yes, that's what I found. I pulled the plug and the gauge went to full. That means the gauge is good, right? Does this also mean that both sending units are in disrepair by having poor contact or having floats that are damaged which means I need to replace them?
If I have to replace them, is it easier to pull the truck bed off the frame and gain access to both units without dropping the tanks?
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Yes, that means the gauge is good. Not sure about the resistor. If both the resistor is open and the sender wire is open, I'm not sure you won't see FULL anyway.
Can you put a 90-ohm resistor (from Radio Shack; a 1W resistor will be fine for this test) between the sender wire and ground? This should also result in a full reading, but it will read 1/4 or 2/5 if the resistor is broken. Should be PNK wire, I think, between a PNK/WHT and a PNK/BLK, on one end of the connector.
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When I get the resistor from RS where exactly do I put it when I am putting it between the sender wire and the ground? At the back of the gauge or at the widget or somewhere else? Sorry for the need for further explanation but I am not as well versed in the technical stuff as I wish I was.
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For ground, the frame rail will do. By sender wire, I mean the wire back to the gauge. This should be the pink wire on the connector you pulled off the valve. It should be between a pink wire with a black stripe and a pink wire with a white strip. These three wires should be clustered on one end of the connector. So you put one end of the resistor into the connector position with the pink wire, and jumper the other end to ground, which is the frame rail, the sheet metal, pretty much any place you can find some bare metal under there.
If the resistor is OK, the gauge will stay at full. Then it must be the sender units. If it drops to 1/4 to 2/5, then the resistor is bad.
Pulling the box off to get at the sender wires is a PITA. So is stripping the instrument panel back to get to the resistor, though not as bad. Knowing which you need to do, so you don't guess wrong and end up doing both, is worth some experimentation.
I doubt the senders, because there are two of them and they would both have to fail in the exact same way to get what you are seeing.
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BTW, how many wires are on your connector, five or six?
It's probably a six-position with five wires. The one empty position is on one end. If you call that empty position "1", and count across the connector, then the gauge wire is "5".
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I had this problem already. Mine read 3/4 all the time in both tanks. Senders were new, gauge was good. Mine had failed inside the selector valve. It was switching mechanically but not electrically with the soleniid inside of it. New selector valve and everything reads correct.
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If you ground the wire does it go to empty? Even better if you have a fixed 45 ohm resistor you can see if it swings to the middle. So it's odd that both tanks do exactly the same thing. I would check the wiring and am assuming everything else is stock and functional. What switch do you have in the dash?
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I'll try the 45 ohm. Didn't try grounding it yet. All equipment is stock including the switch in the dash.
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Okay, so the gauge goes to full when I unplug the widget completely. I picked up the 90 ohm, 1 watt resistor suggested from Radio Shack and tested it. When I plugged into the 5th wire recommended above and grounded the other end to the frame, the gauge goes to 2/5 full just like it does when the tanks have that much or more in them. From what you all have told me, it appears the fuel resistor is bad on the back of the gauge. I found this one on ebay and I would love for someone to confirm it is the correct one before I purchase it. Thanks for all the assistance!
http://www.ebay.com/itm/Camaro-Nova-Ventura-Resistor-Console-Fuel-Gauge-/131058467349?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AChevrolet&hash=item1e83b18215&vxp=mtr
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That'll work. The same resistor/gauge setup was used from 1965-1997 on almost every GM car and truck.
Here is another, a bit cheaper, and it's a reputable supplier and a reliably new part. This is where I got mine and it was correct and fixed my gauge. eBay can be hit or miss.
http://www.classicmuscle.com/p-6237-fuel-gauge-resistor.aspx
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SUCCESS!! I bought the resistor I linked above from a seller on Ebay (Classic Industries part) and swapped my old one out. The gauge now works perfectly for both tanks! Thanks so much for all of the advice and expertise! You guys saved me a ton of headache. This forum is awesome!
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Excellent. Thanks for letting us know. It keeps the knowledgebase growing.
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Okay...maybe I celebrated too quickly? The resistor I bought seems to be wrong. When the tanks are full the gauge goes way past full...like another half of a tank past full (3:00 to 4:00 position). Any suggestions?
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too much resistance. an open ground is infinite ohms so the resistor is allowing and/or adding more resistance than the 0-90 the gauge is set for.
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Can you recommend a course of action to locate and eliminate the problem?
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Are you saying that there is a ground that is not good which is causing infinite resistance? i noticed that the gauge seems to read correctly when the truck is off but as soon as the power is on it dives to the right.
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Going further than full, to say the 3 o'clock position, is an open circuit on the ground side. Check the ground connection on top off the tank.this will be a push on post style connector, then follow that wire to the frame, check that. Then make sure the pink wire from tank/fuel selector valve if you have dual tanks, is not broken. Check ground side of resistor and then check ground pin on gauge. Any bad connection will result in going past full.
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Can you recommend a course of action to locate and eliminate the problem?
You need to determine whether the symptoms originate from the dash gauge, the sender, or the wiring...
If the prior posts haven't lead you to a solution, disconnect the fuel gauge wire from the tank sender and substitute the 90-ohm resistor as you did before between the pink wire and a good clean ground. Switch the ignition ON. Does the fuel gauge indicate exactly Full?