Well, I pulled out the fuel sender and pulled apart the float level sender. Cleaned the contacts and windings as stated and put it all back together. It now works (doesnt read full all the time anymore) however I believe it is still off some. I think it is reading higher than what is listed in the tank. How many miles (around town, non highway) should I see out of a tank of gas with mild throttle agressiveness ? Also.....mike88z51, sorry I didnt see your post about taking pictures until now. Great idea though. If I pull it again (I doubt I will) then I will take some. Sorry man.

 

Your car has a twenty gallon tank. If you count the bars you will see that 1 bar = 1 gallon.I usually get 350 or so miles to a tank but have gotten 500 on the long trips.

 

Did you clean the three brass contacts just under the mounting flange?

They turn black with corrosion over time and can cause problems with the FP as well as the level sender.

 

I'm getting ready to do the same surgery on my 84. How hard is the sending unit to get apart?

I'm sick and tired of having to reset the trip meter every time I fill up.

 

It is a real easy job. The whole fuel pump sending unit assembly is held in by 10 bolts. Be sure to get a new assembly gasket from the dealer and pick up a couple of replacement o-rings for the assembly bolts. Usually one or two of the o-rings is warped or crushed. Shouldn't cost more than $15.

You remove the fuel tank cover door and then the 10 bolts. You have to twist the assembly at some odd angles as you pull it out, but it does come out without bending or breaking anything. When you have it out, there is a small metal "container" that the float arm goes into. This is the fuel guage sending potentiometer. It is held together by bent metal tangs. CAREFULLY bend the tangs enough to open the sender. Inside is a button on the end of the float arm that moves across the windings in the side of the container. Clean the button with very fine sandpaper or emery cloth and WD40. Be gentle.

Wipe the windings with a cloth and some WD40. Rub off any accumulated grime/corrosion. DON'T SAND THE WINDINGS! Be gentle as they are very fine wires. Check that the float arm moves freely and isn't binding due to corrosion at the pivot point. You can attach an ohmmeter to the wires to the fuel gauage sender and should see the resistance change from ~90 ohms to ~0 as you move the float arm. If everything checks out, bend the tangs back into place to close the potentiometer container.

Clean the other external brass contacts on the assmenly as 65Z01 mentions and put the entire assembly back in the tank. When putting the new assembly gasket on be sure to orient the notch so that it is in the upper right hand corner. It matters or the notch wouldn't be there. (Don't ask how I know.)

You are working with a fuel tank and a highly flammable fuel. Have a fire extinguisher available and ready at all times. If possible take lots of digital pictures and let's write up a tech tip for others.

 

Mike....excellent description. I'm off this friday, and didn't have anything planned, so good time to tear into it. Does the Chevy dealer usually stock the gaskets, or should I order one from MAD, Ecklers, CC etc first?

I will take some digital shots and post them as I go. Would be a great tech article, as I think the cost of these sending units is highway robbery. Man it would be nice to have a working fuel gauge again.

Also will have an extinguisher handy and will tape off the opening while I have the pump assy apart.

Thanks again for the info.

 

The Chevy dealer should have a gasket and some o-rings in stock. If not, have them run a dealer wide search. They can poll all Chevy dealer parts availability in the USA and get an answer in 60 seconds. I've often had one dealer say a part wasn't in stock and they can find it available at the next nearest dealer on the other side of town. I covered my tank opening with a piece of cardboard cut to fit.

It is possible that there is something fundamentally wrong with your sender, but in 99% of the cases I've seen, the sender can be cleaned and made to work like new again. You might also get a cheap syphon hose kit (approx $5) and use it to syphon out any water in the tank. It will look like snot in the bottom of the tank and should be easily visible and removable.

There have been several others who have experienced this problem lately, so a Tech Tip will be beneficial to all if you take the pictures.

Good luck, keep us posted.

 

You have inspired me to take apart the sender and clean it when I put in the Racetronix fuel pump this week.

 

Our new C4 pump kits being released next week will include a new Racetronix C4 tank gasket, new SS Allen head bolts w/o-rings, Allen key, completely new in-tank Teflon wiring (no adapters), grounding clamp, foam sleeve, pump mount, hose clamps, FI hose, and of coarse a Walbro GSS340M 255L/Hr HP pump.

Some kits shipped over the past week or two have included some of these items.

 

Hello boys !!
I have also an funny problem with my fuel meter, When I have car on ignition, but not started, the meter shows one level, but when I start the car the green lines in the dashboard rises several steps. Could this also be a sender fault, I already tryed to make an extra ground for the dashboard, but there was no improvment.
:confused:

 

My GSS307M kit shipped monday. Will it include these upgrades?

 

It will include the gasket kit and associated hardware.

 

:hurray:

 

Just a sender update.

My dash gauge has been inaccurate for a long while, I just never got around to trying to sort it out.

I just finished pulling the pump and using a digital volt meter, I found that with the float at its lowest position (empty tank) I had a reading of 10 ohms.

At the highest position (full tank) I had 110 ohms.

The manuals says it should have read ZERO ohms at empty and 90 ohms at full.

So after cleaning all the contacts with no change in the readings, I jacked around with the the float arm until I was able to get .5 ohms at empty and 90 at full.

I haven't re-installed it yet to test whether I solved the problem because I had to use some JB Weld (steel) on one of the little clips which broke off. they are very fragile and I WAS being careful.

As soon as the JB cures, I'll re-install everything and see if I corrected the problem.

I also checked the float arm through its full range of travel (just as you do when checking the TPS) and the readings seemed to be linear.

I'll post the results.

Jake

 

You can also just buy some resistors at Radio Shack and make various 'resistor packages', say 90 ohm and 45 ohm, plug it into the harness to test the guage and wiring before reinstalling the sender.

I hope your results are good, because ever since I changed my fuel pump, my gauge has been off. I haven't taken it out to clean yet but it does bug me.

 

That's something I hadn't considered after my bad experience with car speakers. I had a set of 4 ohm car speakers and wanted to use them in my home system that calls for 8-16 ohm speakers.

I soldered in a 4 ohm resistor in the hopes of raising the ohms to 8, but no sound would come through the speaker after I did it. So I just scraped that plan.

Just for my info, since I was getting 10 ohms, but wanted to have ZERO ohms, how could I reduce the resistance using a resistor?

Thanks,

Jake

 

The fuel sender is wired like a rheostat or current limiting device which is variable based on fuel levels - so you can't.

The examples below really only work when fixed resistance is required.

Resistors when wired in series (end to end), have their values added together. The same value resistors wired in parallel have half the resistance of just one.

Say you need 20 ohms and only have 10 ohm resistors wired them like this
--R--R---

If you have 10 ohm resistors and need 5 ohms wired them in parallel like this

----R----
----R----


[Modified by 1MoorTym, 10:33 PM 5/6/2004]

 

1MoorTym is absolutely correct. In order to reduce overall resistance you add resistors in parallel. The resultant resistance equals the inverse of the fractions added together or 1/R = 1/R1 + 1/R2. Two 10 ohm resistors in parallel = 5 ohms. Three 10 ohm resistors in parallel = 3.33 ohms. Using parallel resistance the only way you could drop resistance to ZERO is to have one side be ZERO (or a jumper wire).

At best adding a parallel resistance of say 1/2 ohm to your existing 10 ohm minimum value would result in a final value of 1/R = (1/10 + 2/1) = (1/10 + 20/10) = 21/10 => final resistance of 1/2.1 or just less than 1/2 ohm. At max sender resistance of 90 ohms the result is 1/R = (1/90 + 2/1) =( 1/90 + 180/90) = 181/90 => final resistance again of just under 1/2 ohm. The path of least resistance in essence grounds out the variable resistance of the sender. This defeats the purpose of the variable resistance sender.

If you can't get the sender to read ZERO ohms try to get it as close as possible by cleaning and adjusting the arm movement. Even if it is off some, as long as it changes resistance in a linear way, it should make the gas guage usable across a range, if off by a given number of bars/gallons to start with.

Swede, since your values change depending on whether the engine is running or not, it is my GUESS that there is a voltage/resistance/grounding issue in the wires leading to the sending unit if it isn't the sending unit. With the engine opeating and the alternator providing more than 12 volts you get one reading. When the engine is off the voltage level drops to 12 volts or less giving you a different reading. There is an external ground wire attached to one of the 10 fuel pump assembly bolts which might need some attention. Check it and the wires to the FP and sender assembly. That might fix the problem without removing the assembly.

Good luck..


[Modified by Mike_88Z51, 5:36 AM 5/7/2004]

 

Thanks my friend !!
I will go home and check this asap. I hope it could be thet simple.
//Magnus

 

Well, here's the latest.

When I removed the fuel pump to try to fix the erroneous gauge reading, my tank was getting close to empty, but was showing almost half a tank on the gauge. I looked inside the tank and saw that the fuel level barely covered the tray that the float rides in.

After the mods to bring the ohm readings in line, I re-installed the pump and started the engine. The guage then read 'RESERVE" with two green bars showing.

I counted the bars and have only 16, not 20 as someone else posted. I guess the number of bars varies with the year of the car.

I filled the tank to the brim and the gauge went to the full position, showing all 16 bars. Took 18.03 gallons.

Now, I have to drive the car and watch how linear the gauge drops with gas usage. I plan to wait until the gauge hit half full, then I'm going to re-fill the tank and see what it will hold. Should take around 10 gallons at that point.

So far so good though.

BTW, my ground wire is soldered to the cover with what looks like factory installation; it isn't attached to one of the cover bolts.

Jake