Fuel Gage reads full+half more

Tiny
RICKJ41
  • MEMBER
  • 1987 CHEVROLET SILVERADO
  • 255,000 MILES
I own a 1987 Chevy Silverado 3+3 1 Ton Dually. I recently replaced the Dash Fuel Tanks Switch. My Passanger Tank reads correctly, but the Driver's side Tank reads Full + a Quarter? Is the Float Damaged or something else? The Tank Swith went up in smoke which is why I had to replace it and about three ft. Of wire. I used the same gauge wire, with the same Ohm/Amp readings.
Do you
have the same problem?
Yes
No
Wednesday, September 14th, 2011 AT 10:19 PM

7 Replies

Tiny
DRCRANKNWRENCH
  • EXPERT
There is an electronic device called a Thermistor that usually indicates low fuel. However, they can affect float reading if not grounded properly. Double check your grounf or even make another ground from pump to frame. If that does not work, the thermistor in the tank or the fuel level indicator may be not connected well or grounded well.
Odd that you got good multi-meter reading though. Regardless, in the tanks the could be bachfeeding into the wrong ground.
Was this
answer
helpful?
Yes
No
Wednesday, September 14th, 2011 AT 10:32 PM
Tiny
RICKJ41
  • MEMBER
Dr. CrankWrench, Thank you for your quick response. I think I need to clarify my question. I replaced the Fuel tank Selector Switch that started smoking while I was driving, and then my truck acted like it had run out of gas and stalled. I had almost half a tank in my Driver's side tank. I pulled off the front cover of the selector switch and managed to use the tip of a Bic pen to move the inside of the switch to my passenger side tank. It finally started. I replaced the burnt wires that had melted about three inches each. I matched the wires from an Auto Electric shop and they said the wires had to match as I assumed that one or two wires had to be "Resistor" wires, but all four were Copper. I did not get under my Truck; I am disabled and am unable to crawl under my truck. To be honest I don't even know where the Fuel Pump is! Is there a fuel pump in each tank? Why would my passenger side tank register correctly, but my driver's side tank reads at the 3:00 position? It still pulls gas from that tank, but I never really know how much gas is in it. I have a Chevy Truck Manual, but it's so generic, it doesn't show where the fuel pump or the Thermistor is. I'm sorry I can't contribute to your web site as I live on a fixed income. Your site is the cheapest compared to the others I've checked where the minimum is $18.00. I'm very grateful for your help. I did Smog Checks, Repairs, and Performance Tuning for over Fifteen years, but have developed severe breathing problems as I ve had Asthma my whole life. Thank you again for your time and help. Respectfully, RickJ41
Was this
answer
helpful?
Yes
No
-1
Thursday, September 15th, 2011 AT 12:55 AM
Tiny
DRCRANKNWRENCH
  • EXPERT
Thanks you for your kind words. That is the best payment of all. Not many people say thanks and one someone does it makes you feel real good that you could help.
Now, as far as the selector goes that you pushed with a pen, is that all elecrtric?
You might have burnt out the thermistor on the on tank and can't get to the wore. Most fuel pumps are in the tank but some are not and I don't have a schemeatic for your truck. If we need to get one, I will try to find one.
For now look at the wiring diagram in the back of the manual and see how many wires come off the slector and you should also be able to locate the pump.
Its not too hard once you start somewhere you are familiar with.
Let me know how it goes.
Was this
answer
helpful?
Yes
No
Thursday, September 15th, 2011 AT 5:37 AM
Tiny
RICKJ41
  • MEMBER
It's an all plastic Switch. I couldn't get to it from behind the dash, so I pulled the front of the switch off. The lever on the front of the switch was melted on the inside. I could see how the switch-lever moved up or down. I took the pointed end of the Bic cap and pushed it in, then up, switching it from the Driver's side to the Passenger Side tank. There were four wires on the back of the switch. The top two were melted and very hot to the touch. I live in the high desert, and it was 110 degrees outside, of course, plus I was stuck in Traffic. The Switch is all electric except for the "toggle up and down" part. I'm using a Haynes Repair manual # 24064, I really miss the Big Chilton Books!The Haynes manual is useless, there are six different Illistartions on Chassis Electrical. Fuel Pump location is not mentioned, but the color wies are Tan In, Blk/Wht to grnd. Fuel Pump Relay and Pump Primer-Red in/Tan/Wht Out. Page 12-17 on the Haynes manual. Sorry I can't be more specific. I should take it to a Muffler Shop that has a Rack big enough to lift my truck so I can actuall look and write down the Color of the wires and where they go. The last time I got to check it out, it looked like an Octopus full of Hoses, Wires, and a Switching Valve with about three or four metal lines going to and from it. Thank you again for your help. RickJ41
Was this
answer
helpful?
Yes
No
Thursday, September 15th, 2011 AT 5:24 PM
Tiny
DRCRANKNWRENCH
  • EXPERT
The Chiltons were great. You could get near factory level and not pay sometime several hundred to get the factory one.

Since the switch is melted inside, you have to have a short somewhere, possibly in the dash which might help explain the fuel level issue.

If you look in the back of the Chiltons, thee should be wiring diagrams, (I don't remember but the Haynes do), you can look up the diagram for the fuel system and look for the pump and then look for the colored wires. Then you can trace them to see where they go.
If the truck is running, at least one thing is sure, the relay is working. I do not know if they have seperate relays and pumps. You could find that out in the wiring diagram.
I think putting on a lift will help, but a lot of the wires run down the drivers side under the carpet and then if any are under the truck you will have to remove some of the plastic shielding which is heald together with electrical tape.

On the tank there should be a feed hose for each tanks, a return line for each tank, (which is the high pressure hose), and a vent for each tank. Then you also have the filler necks and vents for the filler neck. Yeah, that an octopus.

It sounds like there a re two internal tank, (In Tank), pumps and those are the feed and return lines for each. That menas you probably blew out the electrical for the one tank with a short somewhere, That is a scary thought having an electric pump in a tank of gas, ain't it?
There are probably 2 relays one for each pump and the switch melted when the one circuit blew and it is having an effect on the fuel gauge by backgrounding or soemthinig.

You can use wiring diagrams to see what goes where. However I think you're going to have to trace down a short or the one pump seized up and burnt the wiring up. That means the tanks might have to be dropped some to get them out. Then if it is not the pump you still need to find the short.

Try looking at the diagrams and what you replaced wiring wise and I bet you will figure it out.
Was this
answer
helpful?
Yes
No
Thursday, September 15th, 2011 AT 6:08 PM
Tiny
RICKJ41
  • MEMBER
Thank you again for your help Dr CranknWrench. I'll do the best I can. It still pulls fuel from both tanks which is a good thing. Next month I'll try and get it to a friends Muffler Shop and see if he'll let me put it on his Rack. The pumps in the tanks are still good or my driver's side tank wouldn't pull gas from it, right? There's no way I can drop either tank, I'd rather find another burnt wire causing the over-full gauge problem. Again thank you very much for your time and help. Over the years I've tried to help others who were unable to pay and repair their auto. I even got a home-made Apple Pie and a Bottle of wine-even though I don't drink. There are a few good and honest Mechanics out there still, but to be honest we are a dying breed, you know? I'll let you know how this issue all washes out. I'll also recomend you and your Great Web-Site to all of my retired Automotive friends. God's speed, RickJ41
Was this
answer
helpful?
Yes
No
Thursday, September 15th, 2011 AT 6:24 PM
Tiny
DRCRANKNWRENCH
  • EXPERT
Thanks you and God Speed with your moments as they go too.
I thank you for your appreciation as it is as good as pie or a drink. Sometimes I think the biggest thing taken for granted in this world is other people. We are here to help each other out. What goes around comes around. I know I will get help 3 times over one day when I need it.
Thank you sir and I know all will be fine with your truck. Electrical diagnosis is the most frustrating thing. But you'll get it.
Was this
answer
helpful?
Yes
No
Thursday, September 15th, 2011 AT 6:32 PM

Please login or register to post a reply.

Recommended Guides