C4 Gas Gauge
03-21-2019, 10:40 AM
#2
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Probably the float is bumped up against the yellow retainer it sits in, but take the whole assembly out and make sure nothing is wrong with how the float moves. Check the purple wire inside the tank that runs from the float to the mount too, its probably not frayed or loose but its worth checking.
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EOC (03-21-2019)
03-21-2019, 11:30 AM
#3
Safety Car
Welcome to the Corvette Forum, we are glad you are here!
The information that Vader86 gave you is good stuff, that would be one of the first things you would want to check. The wiring going to the sending unit should be checked anyway. The Fuel pump is mounted on a assembly that fits down into the tank and it requires some gentle wiggling to get it in the right spot sometimes. That alone could mess up your fuel gauge. Sometimes the grounds are not grounded well enough and that too can upset the fuel gauge readings.
The fuel filler cap has a plate underneath the cover that can be removed. From there you disconnect the wire connector and then oil the bolts holding the pump assembly in the tank. I would douse them well with a GOOD penetrating oil like KROIL OIL or WD-40 and let it set before removing the bolts. I say this because they rust in place and break off easily if not lubed up with penetrating oil. If they are still being tough to remove use a hot air gun and heat up the bolts and again coat them with penetrating oil so they will break loose and not break off. Somebody broke off two of my bolts so I removed the pieces and fixed it so it won't leak gasoline.
The wiring harness for the fuel pump and float assembly only has three wires. The red big one is 12 Vdc for the fuel pump, the second wire I think is the ground and the third (Purple) goes to the float assembly. After removing the sending unit and pump from the car take a multimeter and check the resistance between the purple wire and the ground. It should change numbers all the way through going high to low or vice versa if the sending unit is okay. Please be VERY careful and have a fire extinguisher nearby when you are checking this stuff out.
Is this your first Corvette or are you and old hand at Corvettes? If you don't have one you should get a set of the Factory Service manuals from Helm Publishers, they are very important to have if you plan on keeping a C4. Another critical tool is a fuel pressure tester as many of the woes of C4's comes from the fuel system and it's many parts.
Anytime you have questions we are here! In the future you should post what year, model (we know it is a Corvette! Rag top or hard top) and anything relevant to the problem at hand. The more information you supply the better the answers will be. We frequently put year and type on our "profile page".
Good Luck and enjoy that Corvette!
Chris a.k.a. ctmccloskey
The information that Vader86 gave you is good stuff, that would be one of the first things you would want to check. The wiring going to the sending unit should be checked anyway. The Fuel pump is mounted on a assembly that fits down into the tank and it requires some gentle wiggling to get it in the right spot sometimes. That alone could mess up your fuel gauge. Sometimes the grounds are not grounded well enough and that too can upset the fuel gauge readings.
The fuel filler cap has a plate underneath the cover that can be removed. From there you disconnect the wire connector and then oil the bolts holding the pump assembly in the tank. I would douse them well with a GOOD penetrating oil like KROIL OIL or WD-40 and let it set before removing the bolts. I say this because they rust in place and break off easily if not lubed up with penetrating oil. If they are still being tough to remove use a hot air gun and heat up the bolts and again coat them with penetrating oil so they will break loose and not break off. Somebody broke off two of my bolts so I removed the pieces and fixed it so it won't leak gasoline.
The wiring harness for the fuel pump and float assembly only has three wires. The red big one is 12 Vdc for the fuel pump, the second wire I think is the ground and the third (Purple) goes to the float assembly. After removing the sending unit and pump from the car take a multimeter and check the resistance between the purple wire and the ground. It should change numbers all the way through going high to low or vice versa if the sending unit is okay. Please be VERY careful and have a fire extinguisher nearby when you are checking this stuff out.
Is this your first Corvette or are you and old hand at Corvettes? If you don't have one you should get a set of the Factory Service manuals from Helm Publishers, they are very important to have if you plan on keeping a C4. Another critical tool is a fuel pressure tester as many of the woes of C4's comes from the fuel system and it's many parts.
Anytime you have questions we are here! In the future you should post what year, model (we know it is a Corvette! Rag top or hard top) and anything relevant to the problem at hand. The more information you supply the better the answers will be. We frequently put year and type on our "profile page".
Good Luck and enjoy that Corvette!
Chris a.k.a. ctmccloskey
03-22-2019, 09:22 AM
#5
Safety Car
https://www.corvetteforum.com/forums...h-article.html you can try this ,all of the sending units are not made the same but all work the same . You can take it out ( will need a new gasket ) look on line I found some for $7.95 NOT $35.00 + as you will se some going for same gasket heck Corvette world here in Houston wanted $65.00 for one yep $65.00 RIGHT . WAS thinking about buying some of the $7.95 0nes and selling some to them for $30.00 LOL .. anyway .. You can take out the unit and plug in the plug turn the key to run ( Don't try to crank just run ) and move the float back and forth and watch the fuel gauge move up and down to see if the unit is working or not ( has a delay in it ) so it may take a few minuets to react to the movements . You can try cleaning it but be very careful with it very careful . Look at the thing watch the small leaver move back and forth the leaver has be be touching the little flat peace with the very small copper wire wrapped around it ,it may not be touching it all the way it may have lost it's spring might have to VERY easy bent it back a little to make sure it is touching the copper wire deal .. ( I don't know the name of the little deal ) THE TANK WILL HAVE GAS IN IT SO BE VERY CAREFUFLL >> If all else fales Gulf cost Corvettes has a new ones for around $125.00 not a bad price WAY better that sitting on side of the road out of gas .. Good luck and BE CAREFULL.. GAS..
03-22-2019, 01:54 PM
#6
Safety Car
The points made above are all very good ones. Do not try to use anything but real fiber or rubber gaskets under the tank opening. Silicone will not last there with the gasoline constantly in contact.
After thinking for a while I would suggest that you remove the sending unit and pump and disconnect it from the car and test it away from fuel fumes. You CAN do it on the car as radar502 suggests but it might be a bit safer out and away from the fuel tank.
Disconnect the fuel gauge sender connector and connect on lead to to Terminal B (purple) and the other to terminal A (Black) of the harness half going to the sending unit. Set the resistance setting on your meter and at full you should get 90 ohms at full, 45 ohms at 1/2 tank and Zero ohms when empty. This works on the 1988 C4's at least. When I first replaced mine I bent it ever so slightly but it was not fun trying to make it work after that so I bought a second one and chalked it up to experience. Be very careful and remember the twists you made to get the original out of the fuel tank.
One last thing, IF you remove the fuel pump/sending unit assembly check the conditions of the hose or pulsator that is connected directly to your fuel pump. Many of us remove this gadget and replace it with a short section of Fuel Injection Hose that is made to be submersed in fuel. I also replaced the clamps on the fuel lines and used the newer fuel injection style clamps. Buy this part from a reputable Corvette parts house or deal with the consequences. Have you ever checked the fuel pressure or replaced the fuel pump? It might be a good time to do so while the assembly is out of the tank. My tank had a lot of junk floating around in it so I drained out the gasoline and filled it with water and then wet vacuumed the water out with the crap that was on the bottom of the tank. Using a Fish tank gravel cleaner might provide the same results without draining the gas out first. I just could not leave all that junk in there.
Don't forget to have a Fire Extinguisher handy! This past winter while trying to start a snow blower I once again learned why I keep fire extinguisher handy. The idea of a fuel pump sitting under all that gasoline with the connectors in the fuel as well makes me a bit nervous. I am slowly getting used to the idea....
Good Luck as you are getting closer to the cause of the issues with your Corvette! It won't be long now!!
After thinking for a while I would suggest that you remove the sending unit and pump and disconnect it from the car and test it away from fuel fumes. You CAN do it on the car as radar502 suggests but it might be a bit safer out and away from the fuel tank.
Disconnect the fuel gauge sender connector and connect on lead to to Terminal B (purple) and the other to terminal A (Black) of the harness half going to the sending unit. Set the resistance setting on your meter and at full you should get 90 ohms at full, 45 ohms at 1/2 tank and Zero ohms when empty. This works on the 1988 C4's at least. When I first replaced mine I bent it ever so slightly but it was not fun trying to make it work after that so I bought a second one and chalked it up to experience. Be very careful and remember the twists you made to get the original out of the fuel tank.
One last thing, IF you remove the fuel pump/sending unit assembly check the conditions of the hose or pulsator that is connected directly to your fuel pump. Many of us remove this gadget and replace it with a short section of Fuel Injection Hose that is made to be submersed in fuel. I also replaced the clamps on the fuel lines and used the newer fuel injection style clamps. Buy this part from a reputable Corvette parts house or deal with the consequences. Have you ever checked the fuel pressure or replaced the fuel pump? It might be a good time to do so while the assembly is out of the tank. My tank had a lot of junk floating around in it so I drained out the gasoline and filled it with water and then wet vacuumed the water out with the crap that was on the bottom of the tank. Using a Fish tank gravel cleaner might provide the same results without draining the gas out first. I just could not leave all that junk in there.
Don't forget to have a Fire Extinguisher handy! This past winter while trying to start a snow blower I once again learned why I keep fire extinguisher handy. The idea of a fuel pump sitting under all that gasoline with the connectors in the fuel as well makes me a bit nervous. I am slowly getting used to the idea....
Good Luck as you are getting closer to the cause of the issues with your Corvette! It won't be long now!!
