Fuel Gauge Sending Unit Repair Tech Article.
#41
Instructor
the same thing happens to my 85 vette.....I can drive 30 -40 miles and then stopped at a light and it just stalls hard to restart ...howevr after a while it will start again ...this is making driving my 85 very uneasy.
Any one have any ideas what could be causing the bucking and stalling of this brand new engine,fuel filter,pump sock have all been change fuel pressure is 35 lbs and injectors are clean. whooo is me! MIKE
PS...could this be a transmission issue?
Any one have any ideas what could be causing the bucking and stalling of this brand new engine,fuel filter,pump sock have all been change fuel pressure is 35 lbs and injectors are clean. whooo is me! MIKE
PS...could this be a transmission issue?
#42
Driving for a work trip yesterday I filled the tank. I drove 196 miles and the tank was still registering full and 450 miles of range left.
I've either got the BEST fuel economy of any 95 out there or I'll be cleaning my sending unit when I get home...
Thanks for posting this. It may be an old thread but it will prove invaluable to me this coming weekend.
I've either got the BEST fuel economy of any 95 out there or I'll be cleaning my sending unit when I get home...
Thanks for posting this. It may be an old thread but it will prove invaluable to me this coming weekend.
#43
Le Mans Master
the same thing happens to my 85 vette.....I can drive 30 -40 miles and then stopped at a light and it just stalls hard to restart ...howevr after a while it will start again ...this is making driving my 85 very uneasy.
Any one have any ideas what could be causing the bucking and stalling of this brand new engine,fuel filter,pump sock have all been change fuel pressure is 35 lbs and injectors are clean. whooo is me! MIKE
PS...could this be a transmission issue?
Any one have any ideas what could be causing the bucking and stalling of this brand new engine,fuel filter,pump sock have all been change fuel pressure is 35 lbs and injectors are clean. whooo is me! MIKE
PS...could this be a transmission issue?
I have a theory about resistance building up in the windings due to insufficient cooling by the surrounding fuel especially as the tank approaches empty, I haven't thought of a great way to actually test that yet though..
#44
Instructor
wow i love this forum, my 90 just started doing this yesterday and i was crapping bricks but after checking the forums and reading this, i am so excited to do this, i thought i had to replace the cluster and the fuel system... thanks a lot, i will post what happens once i do it, again thanks for your time and wisdom for writing this up!
The following 3 users liked this post by pmihaltian:
#50
Wow this is a great article on how to fix sending unit. My gauge quit on me awhile back. Just replaced my fuel pump and decided to give this a try, now gauge works like a charm. Thanks for posting this Frizlefrak.
#51
I did this job this week using this guide...VERY helpful. I discovered a couple of things that might help other folks. First, maybe my fuse box is different, but I did not readily see a fuse for the fuel pump. However, I found another easy way. I just disconnected the connector for the fuel pump, then I ran the car until it died to purge the fuel. Also, after following the instructions, my gauge still wasn't working. I put an ohm meter across the sending unit and it read open. The problem was the little contact on the springy copper piece...although I sanded it it was actually a bit loose as was the physical connection on the other end of the copper piece. I scraped the copper and soldered those two points. They took solder easily and now my gauge works 100%. Thanks again for the great post!
#52
Race Director
On my car the fuel pump fuse is labelled "FP". It's in the lower right corner of the fuse panel.
Note that the fuse panels changed in 1990, so the FP label and location is probably different.
Note that the fuse panels changed in 1990, so the FP label and location is probably different.
#53
Well I am cheap and did as your article suggested but
Right after I got my 87' i went looking for a cure to fix my sender. I used your article and did all the steps but the sender was shot. Being cheap and very inventive I went looking for a potentiometer replacement. Non were available or ridiculously priced. So I found out the ohms of the stock unit and found a universal replacement sender for $22.00 this unit would not actually work in the car because of the pump and other things BUT the new potentiometer could work if I made a plate to mount it and reformed the float on the universal sender. Then for about another $4.00 dollars for brass plate and screws and rivets I created a perfect replacement. the job took a few hours of fitting and testing which for me was real easy and now my tank level reads perfectly. If you want some info email me.
The following users liked this post:
38Blackneck (03-13-2021)
#54
A couple of years ago, I wrote the tech article for repairing a defective fuel gauge sending unit. It's listed in the C4 tech section of Corvette Forum.
https://www.corvetteforum.com/techti...=277&TopicID=2
I learned the procedure from Corvette Forum member Mike88Z51, who walked me through repairing my sending unit. After thanking him, he suggested I do a write up with pics that we could share with the whole C4 community.
Recently I've had quite a few requests for the article in MS Word format with pics. It seems this problem is pervasive on the C4's...particularly on the earlier models. Many members have also been kind enough to offer suggestions to improve the article and have corrected a couple of errors I made in the initial writing.
So, in order to make the article with pics available to as many C4 owners as possible, I decided to post it in a regular thread. I will bookmark the link for future requests as well, so it's available once the thread is archived. Here's the procedure:
Fuel Gauge Sending Unit Repair
If your C4’s fuel gauge reads full regardless of how much fuel you actually have, the sending unit in the tank is most likely at fault. If you have priced a new sending unit, you realize that they run well over $300. In many cases, however, they can be repaired in about an hour with very little expense. This repair is relatively simple if you have decent mechanical aptitude, and doesn’t require any special tools. I did this repair on my ’84, but the procedures should be similar for all C4’s You should purchase a new fuel tank gasket prior to beginning. They run about $15 at any Chevrolet dealership. Also, have a fire extinguisher handy just in case. Here is how to proceed.
1. First, you must bleed the pressure out of the fuel system prior to removing any fuel lines to avoid being sprayed with fuel. Remove the fuel pump fuse from the fuse box, and crank the car. If it starts, allow it to run until it dies. The fuel pump fuse is clearly marked. On the 84, it is the bottom fuse in the fourth column of fuses.
2. The second step is to remove the fuel filler door. There are 4 phillips screws holding it to the body of the car. Once the door is removed, remove the gas cap and the rubber boot surrounding the filler tube. It has a drain hose that slides off as well. The boot is held in only by pressure, there are no screws or fasteners. You now have access to the fuel lines, wiring, and the fuel tank cover.
3. There are 3 fuel lines. The upper line is the pressure line that runs to the throttle bodies (crossfire) or fuel rail (TPI). The lower right line is the return line, and the lower left runs to the charcoal canister. Clamps hold on each fuel line. Loosen the clamps and remove the hoses.
4. There is a single three wire harness that services the fuel pump and sending unit. There is a small, white plastic clip that must be removed prior to pulling the connectors apart. Compress it with a pair of needle nose pliers and remove it. Now the harness will separate.
5. Remove the nine 10 mm bolts that hold the cover onto the tank. Carefully lift the fuel pump / sending unit assembly out of the tank. It is a good idea to clean any debris from the surrounding area prior to removing the assembly to prevent it from falling into the tank. Place some old rags over the painted surfaces of your car to protect it from any fuel that drips. You will need to gently maneuver the assembly back and forth to get it to clear the opening, but it will come out with relative ease. Here’s what it looks like after you’ve removed it.
6. Gently lay the assembly on your workbench. Now use some duct tape strips to cover the opening of your fuel tank. Fumes can accumulate rapidly, so do this at the earliest opportunity. DO NOT use a rag to cover the opening. This makes an excellent Malatov Cocktail out of your car. If you’re working in a garage, keep the door open for safety!!
Tank taped up….
Garage door open….
7. Now that you have the fuel pump / sending unit assembly on your bench, it’s time to disassemble the sending unit. It is basically comprised of two parts; The float arm and contact, and the body with the windings. It works like a potentiometer / variable resistor in that moving the arm changes resistance, thus telling the gauge how much fuel is in the tank. Malfunctions occur when either the contact or the windings become dirty, rusted, or otherwise don’t make good contact. Once this is corrected, your gauge will once again read correctly.
To disassemble the sending unit, GENTLY pry the three small tabs back just enough to allow the cover with the windings to separate from the assembly. These can break easily, so use as little force as possible. Here is where the sending unit is on the pump assembly.
And a pic of the contact….in the center of the quite rusty sending unit body…
8. Now that it’s apart, use some 600 grit sandpaper and gently sand the CONTACT. DO NOT sand the windings or you will ruin them. The contact is mounted on a thin piece of springy metal, so use a finger behind it to support it as you sand. Sand it until it has a shiny, new surface. Next, soak a Q-Tip in WD-40 and GENTLY clean the windings. Move the Q-Tip with, not against, the windings. They are very delicate, so use only very slight pressure. Here’s what the windings look like…
9. Gently reassemble the sending unit and bend the tabs back into place using only necessary pressure. Ensure that the float arm moves smoothly and doesn’t bind.
10. Connect an Ohm meter or multi-tester as follows: Using an alligator clip, attach the negative terminal to the metal body of the sending unit. Press the positive tip against the wire that leads from the sending unit to the top of the assembly. Move the float arm back and forth and note the changes in resistance. You should have somewhere in the neighborhood of 90 ohms resistance at full, and close to 0 ohms (no resistance) at empty. If you use an analog meter, you can watch the needle swing both ways as you move the float arm. If this happens, your sending unit is now functioning normally again. Time to put it back together again!
11. Use your new gasket on reassembly. You will notice a notch cut into the gasket. This notch goes in the upper right corner, and corresponds to a small ridge on the tank. The gasket will fit in the opposite direction, but it won’t seal and you will have a nasty fuel odor (and safety hazard). Ensure that this gasket goes back in correctly. (NOTE: The Helms manual section 6C-4 indicates that the gasket goes in the LOWER right hand corner. Observe how yours comes apart and you will notice that the gasket won’t fit that way). Here is the gasket you will use.
And the new one and old one next to each other….
12. Position the assembly back into the tank with the new gasket. Again, you will have to do some gentle maneuvering to get it to go back in correctly, but it will slide back into place with relative ease. Ensure that the gasket lined up correctly, and put the bolts back in. Snug them down by hand, and then tighten in a star pattern to about 15-20 ft lbs.
13. Reconnect the wiring harness and remember to slide the plastic retainer back in.
14. Reconnect the 3 fuel lines. Replace the fuel pump fuse, the gas cap, and start the vehicle and check for leaks.
15. Shut the car off. Remove the fuel cap, replace the rubber boot and reconnect the drain tube. Replace the fuel cap and the fuel door.
16. Enjoy once again having a working fuel gauge. Total cost less than $20 and about 2 hours of work.
I hope this helps a few Corvette owners keep their cars running and save a few dollars in the process. I’m certain that this article is a long way from perfect, so anyone having suggestions on how to improve this tech article is invited to submit them by either dropping me an PM or an email. PM Frizlefrak on Corvette Forum, or email me at Dcarson@elp.rr.com.
I will continue to revise it with new or corrected info, and keep the link updated.
Special Thanks are owed to Mike88Z51 on Corvette Forum for teaching me the procedure and suggesting the tech article.
https://www.corvetteforum.com/techti...=277&TopicID=2
I learned the procedure from Corvette Forum member Mike88Z51, who walked me through repairing my sending unit. After thanking him, he suggested I do a write up with pics that we could share with the whole C4 community.
Recently I've had quite a few requests for the article in MS Word format with pics. It seems this problem is pervasive on the C4's...particularly on the earlier models. Many members have also been kind enough to offer suggestions to improve the article and have corrected a couple of errors I made in the initial writing.
So, in order to make the article with pics available to as many C4 owners as possible, I decided to post it in a regular thread. I will bookmark the link for future requests as well, so it's available once the thread is archived. Here's the procedure:
Fuel Gauge Sending Unit Repair
If your C4’s fuel gauge reads full regardless of how much fuel you actually have, the sending unit in the tank is most likely at fault. If you have priced a new sending unit, you realize that they run well over $300. In many cases, however, they can be repaired in about an hour with very little expense. This repair is relatively simple if you have decent mechanical aptitude, and doesn’t require any special tools. I did this repair on my ’84, but the procedures should be similar for all C4’s You should purchase a new fuel tank gasket prior to beginning. They run about $15 at any Chevrolet dealership. Also, have a fire extinguisher handy just in case. Here is how to proceed.
1. First, you must bleed the pressure out of the fuel system prior to removing any fuel lines to avoid being sprayed with fuel. Remove the fuel pump fuse from the fuse box, and crank the car. If it starts, allow it to run until it dies. The fuel pump fuse is clearly marked. On the 84, it is the bottom fuse in the fourth column of fuses.
2. The second step is to remove the fuel filler door. There are 4 phillips screws holding it to the body of the car. Once the door is removed, remove the gas cap and the rubber boot surrounding the filler tube. It has a drain hose that slides off as well. The boot is held in only by pressure, there are no screws or fasteners. You now have access to the fuel lines, wiring, and the fuel tank cover.
3. There are 3 fuel lines. The upper line is the pressure line that runs to the throttle bodies (crossfire) or fuel rail (TPI). The lower right line is the return line, and the lower left runs to the charcoal canister. Clamps hold on each fuel line. Loosen the clamps and remove the hoses.
4. There is a single three wire harness that services the fuel pump and sending unit. There is a small, white plastic clip that must be removed prior to pulling the connectors apart. Compress it with a pair of needle nose pliers and remove it. Now the harness will separate.
5. Remove the nine 10 mm bolts that hold the cover onto the tank. Carefully lift the fuel pump / sending unit assembly out of the tank. It is a good idea to clean any debris from the surrounding area prior to removing the assembly to prevent it from falling into the tank. Place some old rags over the painted surfaces of your car to protect it from any fuel that drips. You will need to gently maneuver the assembly back and forth to get it to clear the opening, but it will come out with relative ease. Here’s what it looks like after you’ve removed it.
6. Gently lay the assembly on your workbench. Now use some duct tape strips to cover the opening of your fuel tank. Fumes can accumulate rapidly, so do this at the earliest opportunity. DO NOT use a rag to cover the opening. This makes an excellent Malatov Cocktail out of your car. If you’re working in a garage, keep the door open for safety!!
Tank taped up….
Garage door open….
7. Now that you have the fuel pump / sending unit assembly on your bench, it’s time to disassemble the sending unit. It is basically comprised of two parts; The float arm and contact, and the body with the windings. It works like a potentiometer / variable resistor in that moving the arm changes resistance, thus telling the gauge how much fuel is in the tank. Malfunctions occur when either the contact or the windings become dirty, rusted, or otherwise don’t make good contact. Once this is corrected, your gauge will once again read correctly.
To disassemble the sending unit, GENTLY pry the three small tabs back just enough to allow the cover with the windings to separate from the assembly. These can break easily, so use as little force as possible. Here is where the sending unit is on the pump assembly.
And a pic of the contact….in the center of the quite rusty sending unit body…
8. Now that it’s apart, use some 600 grit sandpaper and gently sand the CONTACT. DO NOT sand the windings or you will ruin them. The contact is mounted on a thin piece of springy metal, so use a finger behind it to support it as you sand. Sand it until it has a shiny, new surface. Next, soak a Q-Tip in WD-40 and GENTLY clean the windings. Move the Q-Tip with, not against, the windings. They are very delicate, so use only very slight pressure. Here’s what the windings look like…
9. Gently reassemble the sending unit and bend the tabs back into place using only necessary pressure. Ensure that the float arm moves smoothly and doesn’t bind.
10. Connect an Ohm meter or multi-tester as follows: Using an alligator clip, attach the negative terminal to the metal body of the sending unit. Press the positive tip against the wire that leads from the sending unit to the top of the assembly. Move the float arm back and forth and note the changes in resistance. You should have somewhere in the neighborhood of 90 ohms resistance at full, and close to 0 ohms (no resistance) at empty. If you use an analog meter, you can watch the needle swing both ways as you move the float arm. If this happens, your sending unit is now functioning normally again. Time to put it back together again!
11. Use your new gasket on reassembly. You will notice a notch cut into the gasket. This notch goes in the upper right corner, and corresponds to a small ridge on the tank. The gasket will fit in the opposite direction, but it won’t seal and you will have a nasty fuel odor (and safety hazard). Ensure that this gasket goes back in correctly. (NOTE: The Helms manual section 6C-4 indicates that the gasket goes in the LOWER right hand corner. Observe how yours comes apart and you will notice that the gasket won’t fit that way). Here is the gasket you will use.
And the new one and old one next to each other….
12. Position the assembly back into the tank with the new gasket. Again, you will have to do some gentle maneuvering to get it to go back in correctly, but it will slide back into place with relative ease. Ensure that the gasket lined up correctly, and put the bolts back in. Snug them down by hand, and then tighten in a star pattern to about 15-20 ft lbs.
13. Reconnect the wiring harness and remember to slide the plastic retainer back in.
14. Reconnect the 3 fuel lines. Replace the fuel pump fuse, the gas cap, and start the vehicle and check for leaks.
15. Shut the car off. Remove the fuel cap, replace the rubber boot and reconnect the drain tube. Replace the fuel cap and the fuel door.
16. Enjoy once again having a working fuel gauge. Total cost less than $20 and about 2 hours of work.
I hope this helps a few Corvette owners keep their cars running and save a few dollars in the process. I’m certain that this article is a long way from perfect, so anyone having suggestions on how to improve this tech article is invited to submit them by either dropping me an PM or an email. PM Frizlefrak on Corvette Forum, or email me at Dcarson@elp.rr.com.
I will continue to revise it with new or corrected info, and keep the link updated.
Special Thanks are owed to Mike88Z51 on Corvette Forum for teaching me the procedure and suggesting the tech article.
I have used the torque of 40 inch pounds on my 1985 and 1996 Corvettes with no problems.
The following users liked this post:
38Blackneck (03-13-2021)
#55
Intermediate
Thanks
A local Chevy dealer replaced mine @ 4 years ago and it never was accurate from day one. I would take it back and their response was always the same ( it's working properly ) Well it's not and with this insight it will be working properly soon.
A couple of years ago, I wrote the tech article for repairing a defective fuel gauge sending unit. It's listed in the C4 tech section of Corvette Forum.
https://www.corvetteforum.com/techti...=277&TopicID=2
I learned the procedure from Corvette Forum member Mike88Z51, who walked me through repairing my sending unit. After thanking him, he suggested I do a write up with pics that we could share with the whole C4 community.
Recently I've had quite a few requests for the article in MS Word format with pics. It seems this problem is pervasive on the C4's...particularly on the earlier models. Many members have also been kind enough to offer suggestions to improve the article and have corrected a couple of errors I made in the initial writing.
So, in order to make the article with pics available to as many C4 owners as possible, I decided to post it in a regular thread. I will bookmark the link for future requests as well, so it's available once the thread is archived. Here's the procedure:
Fuel Gauge Sending Unit Repair
If your C4’s fuel gauge reads full regardless of how much fuel you actually have, the sending unit in the tank is most likely at fault. If you have priced a new sending unit, you realize that they run well over $300. In many cases, however, they can be repaired in about an hour with very little expense. This repair is relatively simple if you have decent mechanical aptitude, and doesn’t require any special tools. I did this repair on my ’84, but the procedures should be similar for all C4’s You should purchase a new fuel tank gasket prior to beginning. They run about $15 at any Chevrolet dealership. Also, have a fire extinguisher handy just in case. Here is how to proceed.
1. First, you must bleed the pressure out of the fuel system prior to removing any fuel lines to avoid being sprayed with fuel. Remove the fuel pump fuse from the fuse box, and crank the car. If it starts, allow it to run until it dies. The fuel pump fuse is clearly marked. On the 84, it is the bottom fuse in the fourth column of fuses.
2. The second step is to remove the fuel filler door. There are 4 phillips screws holding it to the body of the car. Once the door is removed, remove the gas cap and the rubber boot surrounding the filler tube. It has a drain hose that slides off as well. The boot is held in only by pressure, there are no screws or fasteners. You now have access to the fuel lines, wiring, and the fuel tank cover.
3. There are 3 fuel lines. The upper line is the pressure line that runs to the throttle bodies (crossfire) or fuel rail (TPI). The lower right line is the return line, and the lower left runs to the charcoal canister. Clamps hold on each fuel line. Loosen the clamps and remove the hoses.
4. There is a single three wire harness that services the fuel pump and sending unit. There is a small, white plastic clip that must be removed prior to pulling the connectors apart. Compress it with a pair of needle nose pliers and remove it. Now the harness will separate.
5. Remove the nine 10 mm bolts that hold the cover onto the tank. Carefully lift the fuel pump / sending unit assembly out of the tank. It is a good idea to clean any debris from the surrounding area prior to removing the assembly to prevent it from falling into the tank. Place some old rags over the painted surfaces of your car to protect it from any fuel that drips. You will need to gently maneuver the assembly back and forth to get it to clear the opening, but it will come out with relative ease. Here’s what it looks like after you’ve removed it.
6. Gently lay the assembly on your workbench. Now use some duct tape strips to cover the opening of your fuel tank. Fumes can accumulate rapidly, so do this at the earliest opportunity. DO NOT use a rag to cover the opening. This makes an excellent Malatov Cocktail out of your car. If you’re working in a garage, keep the door open for safety!!
Tank taped up….
Garage door open….
7. Now that you have the fuel pump / sending unit assembly on your bench, it’s time to disassemble the sending unit. It is basically comprised of two parts; The float arm and contact, and the body with the windings. It works like a potentiometer / variable resistor in that moving the arm changes resistance, thus telling the gauge how much fuel is in the tank. Malfunctions occur when either the contact or the windings become dirty, rusted, or otherwise don’t make good contact. Once this is corrected, your gauge will once again read correctly.
To disassemble the sending unit, GENTLY pry the three small tabs back just enough to allow the cover with the windings to separate from the assembly. These can break easily, so use as little force as possible. Here is where the sending unit is on the pump assembly.
And a pic of the contact….in the center of the quite rusty sending unit body…
8. Now that it’s apart, use some 600 grit sandpaper and gently sand the CONTACT. DO NOT sand the windings or you will ruin them. The contact is mounted on a thin piece of springy metal, so use a finger behind it to support it as you sand. Sand it until it has a shiny, new surface. Next, soak a Q-Tip in WD-40 and GENTLY clean the windings. Move the Q-Tip with, not against, the windings. They are very delicate, so use only very slight pressure. Here’s what the windings look like…
9. Gently reassemble the sending unit and bend the tabs back into place using only necessary pressure. Ensure that the float arm moves smoothly and doesn’t bind.
10. Connect an Ohm meter or multi-tester as follows: Using an alligator clip, attach the negative terminal to the metal body of the sending unit. Press the positive tip against the wire that leads from the sending unit to the top of the assembly. Move the float arm back and forth and note the changes in resistance. You should have somewhere in the neighborhood of 90 ohms resistance at full, and close to 0 ohms (no resistance) at empty. If you use an analog meter, you can watch the needle swing both ways as you move the float arm. If this happens, your sending unit is now functioning normally again. Time to put it back together again!
11. Use your new gasket on reassembly. You will notice a notch cut into the gasket. This notch goes in the upper right corner, and corresponds to a small ridge on the tank. The gasket will fit in the opposite direction, but it won’t seal and you will have a nasty fuel odor (and safety hazard). Ensure that this gasket goes back in correctly. (NOTE: The Helms manual section 6C-4 indicates that the gasket goes in the LOWER right hand corner. Observe how yours comes apart and you will notice that the gasket won’t fit that way). Here is the gasket you will use.
And the new one and old one next to each other….
12. Position the assembly back into the tank with the new gasket. Again, you will have to do some gentle maneuvering to get it to go back in correctly, but it will slide back into place with relative ease. Ensure that the gasket lined up correctly, and put the bolts back in. Snug them down by hand, and then tighten in a star pattern to about 15-20 ft lbs.
13. Reconnect the wiring harness and remember to slide the plastic retainer back in.
14. Reconnect the 3 fuel lines. Replace the fuel pump fuse, the gas cap, and start the vehicle and check for leaks.
15. Shut the car off. Remove the fuel cap, replace the rubber boot and reconnect the drain tube. Replace the fuel cap and the fuel door.
16. Enjoy once again having a working fuel gauge. Total cost less than $20 and about 2 hours of work.
I hope this helps a few Corvette owners keep their cars running and save a few dollars in the process. I’m certain that this article is a long way from perfect, so anyone having suggestions on how to improve this tech article is invited to submit them by either dropping me an PM or an email. PM Frizlefrak on Corvette Forum, or email me at Dcarson@elp.rr.com.
I will continue to revise it with new or corrected info, and keep the link updated.
Special Thanks are owed to Mike88Z51 on Corvette Forum for teaching me the procedure and suggesting the tech article.
https://www.corvetteforum.com/techti...=277&TopicID=2
I learned the procedure from Corvette Forum member Mike88Z51, who walked me through repairing my sending unit. After thanking him, he suggested I do a write up with pics that we could share with the whole C4 community.
Recently I've had quite a few requests for the article in MS Word format with pics. It seems this problem is pervasive on the C4's...particularly on the earlier models. Many members have also been kind enough to offer suggestions to improve the article and have corrected a couple of errors I made in the initial writing.
So, in order to make the article with pics available to as many C4 owners as possible, I decided to post it in a regular thread. I will bookmark the link for future requests as well, so it's available once the thread is archived. Here's the procedure:
Fuel Gauge Sending Unit Repair
If your C4’s fuel gauge reads full regardless of how much fuel you actually have, the sending unit in the tank is most likely at fault. If you have priced a new sending unit, you realize that they run well over $300. In many cases, however, they can be repaired in about an hour with very little expense. This repair is relatively simple if you have decent mechanical aptitude, and doesn’t require any special tools. I did this repair on my ’84, but the procedures should be similar for all C4’s You should purchase a new fuel tank gasket prior to beginning. They run about $15 at any Chevrolet dealership. Also, have a fire extinguisher handy just in case. Here is how to proceed.
1. First, you must bleed the pressure out of the fuel system prior to removing any fuel lines to avoid being sprayed with fuel. Remove the fuel pump fuse from the fuse box, and crank the car. If it starts, allow it to run until it dies. The fuel pump fuse is clearly marked. On the 84, it is the bottom fuse in the fourth column of fuses.
2. The second step is to remove the fuel filler door. There are 4 phillips screws holding it to the body of the car. Once the door is removed, remove the gas cap and the rubber boot surrounding the filler tube. It has a drain hose that slides off as well. The boot is held in only by pressure, there are no screws or fasteners. You now have access to the fuel lines, wiring, and the fuel tank cover.
3. There are 3 fuel lines. The upper line is the pressure line that runs to the throttle bodies (crossfire) or fuel rail (TPI). The lower right line is the return line, and the lower left runs to the charcoal canister. Clamps hold on each fuel line. Loosen the clamps and remove the hoses.
4. There is a single three wire harness that services the fuel pump and sending unit. There is a small, white plastic clip that must be removed prior to pulling the connectors apart. Compress it with a pair of needle nose pliers and remove it. Now the harness will separate.
5. Remove the nine 10 mm bolts that hold the cover onto the tank. Carefully lift the fuel pump / sending unit assembly out of the tank. It is a good idea to clean any debris from the surrounding area prior to removing the assembly to prevent it from falling into the tank. Place some old rags over the painted surfaces of your car to protect it from any fuel that drips. You will need to gently maneuver the assembly back and forth to get it to clear the opening, but it will come out with relative ease. Here’s what it looks like after you’ve removed it.
6. Gently lay the assembly on your workbench. Now use some duct tape strips to cover the opening of your fuel tank. Fumes can accumulate rapidly, so do this at the earliest opportunity. DO NOT use a rag to cover the opening. This makes an excellent Malatov Cocktail out of your car. If you’re working in a garage, keep the door open for safety!!
Tank taped up….
Garage door open….
7. Now that you have the fuel pump / sending unit assembly on your bench, it’s time to disassemble the sending unit. It is basically comprised of two parts; The float arm and contact, and the body with the windings. It works like a potentiometer / variable resistor in that moving the arm changes resistance, thus telling the gauge how much fuel is in the tank. Malfunctions occur when either the contact or the windings become dirty, rusted, or otherwise don’t make good contact. Once this is corrected, your gauge will once again read correctly.
To disassemble the sending unit, GENTLY pry the three small tabs back just enough to allow the cover with the windings to separate from the assembly. These can break easily, so use as little force as possible. Here is where the sending unit is on the pump assembly.
And a pic of the contact….in the center of the quite rusty sending unit body…
8. Now that it’s apart, use some 600 grit sandpaper and gently sand the CONTACT. DO NOT sand the windings or you will ruin them. The contact is mounted on a thin piece of springy metal, so use a finger behind it to support it as you sand. Sand it until it has a shiny, new surface. Next, soak a Q-Tip in WD-40 and GENTLY clean the windings. Move the Q-Tip with, not against, the windings. They are very delicate, so use only very slight pressure. Here’s what the windings look like…
9. Gently reassemble the sending unit and bend the tabs back into place using only necessary pressure. Ensure that the float arm moves smoothly and doesn’t bind.
10. Connect an Ohm meter or multi-tester as follows: Using an alligator clip, attach the negative terminal to the metal body of the sending unit. Press the positive tip against the wire that leads from the sending unit to the top of the assembly. Move the float arm back and forth and note the changes in resistance. You should have somewhere in the neighborhood of 90 ohms resistance at full, and close to 0 ohms (no resistance) at empty. If you use an analog meter, you can watch the needle swing both ways as you move the float arm. If this happens, your sending unit is now functioning normally again. Time to put it back together again!
11. Use your new gasket on reassembly. You will notice a notch cut into the gasket. This notch goes in the upper right corner, and corresponds to a small ridge on the tank. The gasket will fit in the opposite direction, but it won’t seal and you will have a nasty fuel odor (and safety hazard). Ensure that this gasket goes back in correctly. (NOTE: The Helms manual section 6C-4 indicates that the gasket goes in the LOWER right hand corner. Observe how yours comes apart and you will notice that the gasket won’t fit that way). Here is the gasket you will use.
And the new one and old one next to each other….
12. Position the assembly back into the tank with the new gasket. Again, you will have to do some gentle maneuvering to get it to go back in correctly, but it will slide back into place with relative ease. Ensure that the gasket lined up correctly, and put the bolts back in. Snug them down by hand, and then tighten in a star pattern to about 15-20 ft lbs.
13. Reconnect the wiring harness and remember to slide the plastic retainer back in.
14. Reconnect the 3 fuel lines. Replace the fuel pump fuse, the gas cap, and start the vehicle and check for leaks.
15. Shut the car off. Remove the fuel cap, replace the rubber boot and reconnect the drain tube. Replace the fuel cap and the fuel door.
16. Enjoy once again having a working fuel gauge. Total cost less than $20 and about 2 hours of work.
I hope this helps a few Corvette owners keep their cars running and save a few dollars in the process. I’m certain that this article is a long way from perfect, so anyone having suggestions on how to improve this tech article is invited to submit them by either dropping me an PM or an email. PM Frizlefrak on Corvette Forum, or email me at Dcarson@elp.rr.com.
I will continue to revise it with new or corrected info, and keep the link updated.
Special Thanks are owed to Mike88Z51 on Corvette Forum for teaching me the procedure and suggesting the tech article.
#56
Melting Slicks
Member Since: Mar 2003
Location: Indianapolis IN
Posts: 3,472
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Finalist 2020 C4 of the Year - Unmodified
C4 of Year Finalist (stock) 2019
Right after I got my 87' i went looking for a cure to fix my sender. I used your article and did all the steps but the sender was shot. Being cheap and very inventive I went looking for a potentiometer replacement. Non were available or ridiculously priced. So I found out the ohms of the stock unit and found a universal replacement sender for $22.00 this unit would not actually work in the car because of the pump and other things BUT the new potentiometer could work if I made a plate to mount it and reformed the float on the universal sender. Then for about another $4.00 dollars for brass plate and screws and rivets I created a perfect replacement. the job took a few hours of fitting and testing which for me was real easy and now my tank level reads perfectly. If you want some info email me.
Dave
#57
Race Director
We need to find out who makes the level sender elements. That would make it much cheaper to fix these things.
I bought one of the new stainless steel level senders and it had a brand new sender element on it. Somebody made that element. Who was it?
I haven't been able to determine who makes the stainless steel level senders. Various Corvette parts vendors are selling them, but they don't tell you who makes it.
I bought one of the new stainless steel level senders and it had a brand new sender element on it. Somebody made that element. Who was it?
I haven't been able to determine who makes the stainless steel level senders. Various Corvette parts vendors are selling them, but they don't tell you who makes it.
#58
Gauge reading wrong.
My 89's fuel level started acting weird. It would read 1/2 a tank, ten minutes later it would read full. Another ten minutes it would be empty. I replaced the whole sending unit, except the pump, with a new one from Ecklers. It is still acting up.
Any suggestions?
Any suggestions?
#59
Race Director
My 89's fuel level started acting weird. It would read 1/2 a tank, ten minutes later it would read full. Another ten minutes it would be empty. I replaced the whole sending unit, except the pump, with a new one from Ecklers. It is still acting up.
Any suggestions?
Any suggestions?
#60
Burning Brakes
help,I just spent2 hours doing the above but I cant get a reading with my meter. I have continuity in the wire(purple) from the connector to the winding connection but when I do as instructed i do not get a reading when I move the float. I even hooked it up to the car and put the key on but no dice..What can be wrong?
I dont want to leave tape over the fuel tank overnight and the door closed. Kevin
I dont want to leave tape over the fuel tank overnight and the door closed. Kevin