Originally Posted by nhlighthouse

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?

Originally Posted by Frizlefrak

Glad to see this is making its rounds and still helping C4 owners have a working fuel gauge.

Originally Posted by Frizlefrak

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.

Originally Posted by Frizlefrak

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.

Originally Posted by Harpmanflys

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.

Originally Posted by Bigbobvette1989

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?