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Fuel Gauge Sending Unit Repair Tech Article.

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Old 12-15-2006, 02:29 PM
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Frizlefrak
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Default Fuel Gauge Sending Unit Repair Tech Article.

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 [email protected].

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.
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Old 12-15-2006, 02:44 PM
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mikey whipreck
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Spectacular

Hopefully some members will use this to cure their hit or miss fuel gauge.
After I did this repair a few months back, my gauge is spot on accurate.
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Old 12-15-2006, 06:34 PM
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Great article. I plan on replacing my fuel pump soon and now will also check out the sending unit. I did not see a fuel filter screen on your picture of the fuel pump. I've never removed my pump and am curious as to where the screen is fitted.
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Old 12-15-2006, 06:44 PM
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Originally Posted by cash's90 View Post
I did not see a fuel filter screen on your picture of the fuel pump. I've never removed my pump and am curious as to where the screen is fitted.

The filter screen, or "sock", is fitted to the bottom of the fuel pump. It's most visible in this pic...




It's the black thing on the end of the pump, just below the float in the pic. Most parts stores require this to be replaced along with the pump or the warranty is voided. The sock is only another $5 or so.
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Old 12-15-2006, 07:46 PM
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Originally Posted by Frizlefrak View Post
The sock is only another $5 or so.
Unless you live in Canada and have more money than brains
as I apparently do. I am embarassed to say I paid Trade Net: $48.65
USF ! for GM #25121216 'Strainer'. That is TRADE in real money,
not Canadian money. Joe off the street would have payed $64.85.

It looked like this


The same item is available from RockAuto for $20 as ACDelco #TS17

RockAuto also sells the following Carter and AirTex sock for $5. You
may see a photo like the canoe above for the Carter - you will
get the sock below, at least I did when I bought the Carter to see
if it was the same as my gold-plated OEM unit from GM.



Some related threads that may be of interest.

Fuel Pump Sock Orientation

Are strainers/socks included w/new fuel pumps

.
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Old 12-16-2006, 11:56 AM
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is this the same setup for a '93
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Old 12-16-2006, 12:10 PM
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Originally Posted by gator79 View Post
is this the same setup for a '93
I think all years fuel injection take the same sock and pump
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Old 12-17-2006, 07:04 AM
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Nice post.
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Old 12-18-2006, 03:39 PM
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great post!! This is my next weekend project!
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Old 12-25-2006, 07:12 AM
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Great post,
I have a 93 Ruby whose fuel gauge has two issues. It reads full until it is close to a half tank, and then the gauge runs down quicker over the next 200 miles. And once it read between half and a quarter tank when we sputtered to a stop, totally out of fuel. Is it safe to assume that sanding the contact and cleaning the windings will correct my problem by freeing up the float?

Merry Christmas to all !
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Old 01-22-2007, 08:06 PM
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rodder robert
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Default gas gauge repair

On my '93 the gauge shown 1/4 full when it was 1/2 full. took the sender out and turned the resistor around, now it works just right!
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Old 01-22-2007, 08:33 PM
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If there was an Oscar for Tech Tips, this one would win it.
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Old 11-24-2010, 09:39 AM
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Nice step by step with pictures thread. I am surprised its 4 years old.
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Old 05-28-2011, 12:26 PM
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Just did this on my 95 lt-1. Took about 30 minutes and now it works great! Thanks much!
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Old 06-22-2011, 12:08 PM
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Another vote for this extremely helpful explanation!! I don't like dredging up old threads, but I searched for this one...easy find and now an easy fix!
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Old 06-23-2011, 08:38 AM
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Mine was sticking here and there.2 treatments of Techron and its now spot on.
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Old 06-25-2011, 02:14 AM
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Great Post I was hoping to find info on my broken fuel gauge since 2002 on my 1995 C4 it reads full until less than a half a tank then it starts going down but never past 3/4... I always fill up aroung 250-300 miles and haven't run out yet. I hope this works, my brother in-law has volunteered to try and fix mine this wknd.
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Old 07-11-2011, 03:15 PM
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I have an 86 Chevrolet Corvette. Yesterday while driving about two blocks it just shutdown. I tried to restart, but all it did was turn over but never catch. I know my gas was low. I got it towed home, put in a 5 Gal can of fuel and attempted a restart. It started up. I left it in the driveway running for about 45 to 50 mins. It ran. Today I started it up took awhile to catch, but cranked, Three blocks up the road and Damn! the same thing happens again. I was near a gas station and my tank was on a half a tank, so I filled up. Waited about ten minutes and she started. Took some cranking, but it started. I proceeded to drive her home. A block away and guess what. She stalled out. Lucky me this happened on top of a hill, so I coasted down.
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Old 07-11-2011, 07:49 PM
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Just wanted to say thanks for posting this thread, I printed it out for my brother-in-law and after 9 yrs I have a working fuel gauge again! He didn't even need to replace the gasket I brought so I will save that for next time.
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Old 07-15-2011, 01:11 AM
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Default Good article, which was shared on C4VR forum -

As a compliment to your great article on fixing the fuel sending unit, one of the members of the C4 Vette Registry (www.C4VetteRegistry.com) posted a link to your article as a fix to another member's plea for help with his gas guage out-a-whack problem.

It is nice to have these forums for Corvetters to share our good and bad among ourselves, as well as our neighbors. It's a great service done by all, for all.

You get the credit, we all get the benefit. Thanks, BAT
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