Fuel Sender Unit

[Rob Peters]

Where have some of you purchased your Fuel Sender Units.  Patsy wants an idea for a Christmas present for me so I may get a fuel sender unit.  Mine is a 70, 350, 2brl so it is my thought that it is just a single tube without a return line.  

I am looking and see many places carry them and there are many different manufacturers.  Has anyone had any better luck  with one manufacturer over another.  Where have you ordered yours from?  Has anyone really had any luck with theirs being a plug and play.

The issue with mine is when the tank is completely full the fuel gauge points almost to the 3:00 position.  I have removed the fuel sender ground position where it is screwed to the body (actually it mounts on the gas tank strap bracket), I have reseated the connector in the trunk but neither of these things corrected the problem.  Joe T was going to put a gauge/meter on it at the Eastern Meet but I was very busy and we never got a chance to check it our with that meter so it seems shot-gunning the problem is my only choice at this point.

rob

[cny first gen 71]

I ordered one from advanced auto but it wasn't like factory unit so I called opg to get a factory unit of course they didn't have but had factory duplicate so I got that one it wasn't accurate.  So I started researching and found I had to bend arm down to make accurate.  While doing that the screen fell off inside of tank so I ended up using the one I got from advanced and it's not accurate either so now I gotta do it again. This time I'm going to test it empty and quater tank and three quarters and full to make sure.  I'm tired of taking the tank out. Good luck with yours.

[Chevy Dave]

I purchased a new gauge from OPGI and a Dorman fuel sender from Amazon.  My fuel gauge reads about 10% higher than it should at 1/2 tank full.

(1970 454 with 2 line sender)

[Scott S.]

21 hours ago, cny first gen 71 said:

I ordered one from advanced auto but it wasn't like factory unit so I called opg to get a factory unit of course they didn't have but had factory duplicate so I got that one it wasn't accurate.  So I started researching and found I had to bend arm down to make accurate.  While doing that the screen fell off inside of tank so I ended up using the one I got from advanced and it's not accurate either so now I gotta do it again. This time I'm going to test it empty and quater tank and three quarters and full to make sure.  I'm tired of taking the tank out. Good luck with yours.

So what you're sayin' is that the "Blue Oval" guys thought this out when they mounted the sender on the side ?????

[Scott S.]

I imagine one could run some wire leads form the tank to the connection and test the gauge for accuracy before installing it......

Just a thought. 

[cny first gen 71]

8 minutes ago, Scott S. said:

I imagine one could run some wire leads form the tank to the connection and test the gauge for accuracy before installing it......

Just a thought. 

Yes I did that exactly, I tested it with it empty and 1/4 tank and worked correctly so I figured it was good. I was wrong so next time I will do more testing before putting it back in.

[jft69z]

4 hours ago, Scott S. said:

I imagine one could run some wire leads form the tank to the connection and test the gauge for accuracy before installing it......

Just a thought. 

I just use a resistance decade box to check the dash gauge. Hook it up in the trunk location at the tan wire & ground, and step it up between 0 and 90 ohms, in various steps (0-23-45-68-90) to check the zero and span. If all is good (or reasonably close) with the dash gauge reading, then the problem is in the sending unit/gas tank area.

If the gauge doesn't read correctly, or at all, you need to investigate further why it doesn't read. 

If you have a spare, known good sending unit on hand, you could hook it up in the trunk as well and go through the range to check the function of the dash readings. Just make sure you hook it to a good ground.

Amazon has some decade boxes, some are even pretty inexpensive for around $16. I'd probably check it with a meter before using it to see if it's fairly close in resistance values though. 

https://www.amazon.com/Decade-Boxes/b?ie=UTF8&node=1265103011

FWIW, the last couple sending units I put in customer cars were Dorman units. Had ordered a 'Spectre' brand for one of them, but didn't like the quality and sent it back.

[John S]

I don’t know what to tell you from my experience I have found they are cheaply made and inaccurate. A number of years ago I took my tank down four times trying different units. I even got an AC Delco sending unit and after using a borescope in the gas tank, saw that the float was resting on the bottom of the tank with a half full tank. I won’t go into detail, but I got very lucky. I called the Parts Place a number of years ago. At that time they had listed an original GM sending unit. I called them. They said they didn’t have one, 20 minutes later they called me back and found one at the back of the shelf. At the time I believe I paid $229 for it but it works great, no adjustment, plug and play, and that was it. So getting back to the original question Don’t know what to tell you. Good luck, and hope you get lucky, because with the sending units that are out there today you’re better to be lucky than good.

John S

[Scott S.]

I've sometimes wondered it the "lead free" fuel available these days has an effect on the float (or what it's made of) ?

[Rob Peters]

48 minutes ago, Scott S. said:

I've sometimes wondered it the "lead free" fuel available these days has an effect on the float (or what it's made of) ?

I don't think it would be the lead free gas so much as the ethanol they add to the gas.  I know that, in the Model A's, the gas gauge was a very simple way of measuring how much gas is in the tank.  It is as simple as the actual indicator that you see through a small glass window is actually inside the gas tank and when it is 3/4 to Full you can see the gas sloshing around in the tank through the little glass window.  Attached to the back of the indicator is a rod and at the end of the rod was a was a simple cork.  From the factory the cork had a coating that the gas would not affect.

When they started adding ethanol to the gas the ethanol/alcohol would eat the coating off of the cork and the cork would eventually soak up the gas and become heavy enough to drop to the bottom of the tank and thus indicate an empty reading on the sight-glass window.  I had to take my Model A gauge apart and install a new float that the ethanol would not affect.  You see, the Model A gas tank is mounted almost in your lap.  It is right above the firewall and just below the windshield.

If the lead free gas affected the Monte Carlo sender unit in the same way I would think the float would drop to the bottom of the tank and always read empty.  Now that you have had a lesson from my Blue Oval Model A we can get back to our beloved Monte Carlo's.

rob 

[Rob Peters]

32 minutes ago, Rob Peters said:

I don't think it would be the lead free gas so much as the ethanol they add to the gas.  I know that, in the Model A's, the gas gauge was a very simple way of measuring how much gas is in the tank.  It is as simple as the actual indicator that you see through a small glass window is actually inside the gas tank and when it is 3/4 to Full you can see the gas sloshing around in the tank through the little glass window.  Attached to the back of the indicator is a rod and at the end of the rod was a was a simple cork.  From the factory the cork had a coating that the gas would not affect.

When they started adding ethanol to the gas the ethanol/alcohol would eat the coating off of the cork and the cork would eventually soak up the gas and become heavy enough to drop to the bottom of the tank and thus indicate an empty reading on the sight-glass window.  I had to take my Model A gauge apart and install a new float that the ethanol would not affect.  You see, the Model A gas tank is mounted almost in your lap.  It is right above the firewall and just below the windshield.

If the lead free gas affected the Monte Carlo sender unit in the same way I would think the float would drop to the bottom of the tank and always read empty.  Now that you have had a lesson from my Blue Oval Model A we can get back to our beloved Monte Carlo's.

rob 

Here are a couple photo's to show the location of the Model A gas tank.  There is no fuel pump on a Model A, it is a gravity feed to the carburetor.

rob

 

[Scott S.]

My John Deere snowmobile had the same gas tank/sender system. The only difference is that it was mounted between my legs. 

As to the "Blue Oval" location reference, if I remember right, the sender unit is accessible without pulling the tank. 

[Chevy Dave]

I like Rob's idea of how to calibrate the float. I recently installed a new Dorman sending unit, and its not accurate.  Let us know if anyone has success with this method.

[Rob Peters]

Well, I had a little time to investigate my gas gauge issue today.  In this thread Joe had provided us with some ideas on purchasing a "Decade Box".  What a decade box enables you do do is control the amount of electricity goes to the gas gauge by inducing resistance into the circuit.  So the troubleshooting goes like this.

First you would disconnect the tan wire in the trunk which is located just to the left of trunk  latch catch.  Once disconnected turn the key to the "ON" position and this makes an "Open" circuit and when this occurs and you turn the gas gauge needle should move to a position somewhere above the Full position.  When I did this my gauge needle went to a position near what would be 3:00 O'Clock position so that was the first step in verifying the gas gauge may be good along with the circuitry to the gauge is working correctly:

(TAN WIRE IN TRUNK DISCONNECTED GAUGE SHOULD READ SOMEWHERE ABOVE FULL)

Now comes the use of the decade box.  When I got my decade box I connected about 15 feet of wire to the box with a small alligator clip to each wire, this way I was not running back in forth between the trunk and the drivers seat.  With the tan wire disconnected from the connector I placed one end on the connector from the tank and the other clip onto the wire going to the front and eventually the instrument panel.  The long wires then allowed me to bring the decade box into the interior so I could, from sitting and watching the gas gauge needle.  

Then you would turn the key to the "ON" position with the decade box set at 0 - 2 ohms the gas gauge needle should read "E"  (Empty).  Below is the reading I got"

(GAS GAUGE NEEDLE READING EMPTY WITH 0 TO 2 OHMS DIALED INTO THE CIRCUIT.  THIS IS A CORRECT READING)

Since my checks are jiving I moved on and dialed in on the decade box and induced 40 to 43 ohms into the circuit.  With the decade box at 40 ohms the needle read a bit below 1/2 so I dialed it up to 43 ohms and that moved the needle straight up at 1/2 tank.  This is exactly what it should read with those ohms applied.  Below is my gauge with 43 ohms applied:

(MY GAS GAUGE NEEDLE READING A 1/2 TANK WITH 43 OHMS APPLIED TO THE CIRCUIT)

This was a correct reading so now I dialed the Decade box to 88 ohms and as I was dialing it in I could see the gauge moving toward the F (Full Position and when I reached 88 ohms the gauge needle showed just above F (FULL).

 

(GAS GAUGE READING CORRECTLY AT 88 OHMS, WITH THE NEEDLE JUST ABOVE THE "F" (FULL) WHICH IS PRECICELY WHAT IT SHOULD READ AT 88 OHMS)

So, what has this told me?  This tells me #1 - the wiring harness going to the front is not a problem.  #2 -  Where the wire comes through into the interior it is not a problem,  #3 - The Cluster circuit board is not the problem and #4 - The gas gauge is good

It appears that my fuel sending unit is defective because it is not inducing the proper resistance into the circuit.  Now, what does not make sense is if I check the resistance at the wire coming into the trunk from the sender unit I am reading over 200 ohms but I do not know how much gas is in the tank.  Since 88 ohms should  cause the gauge to read full gut what the gauge is reading is somewhere between 1/3 and 1/2 full so I would think over 200 ohms would cause it to read way over full.  So what it seems all of this is telling me is the fuel sender unit is bad so I am going to have to empty my tank, drop the tank and replace fuel sender unit.  My only issue will be figuring out how to get it adjusted properly.  before putting the tank back up.

The good thing is in dropping the tank, who knows, maybe i will find another build sheet up there.

rob

 

[jft69z]

44 minutes ago, Rob Peters said:

  My only issue will be figuring out how to get it adjusted properly.  before putting the tank back up.

There really is no adjustment. The new sending unit should be 0-90 ohms thru its span. I'd recommend hooking it up externally first, like you did with the decade box, but with the sending unit instead. Run it thru its range and see if the gas gauge tracks accordingly. 

I usually check the sending unit first with an ohmmeter though, to make sure it had a good, even reading when moving the arm thru its full travel. I've seen bad ones right out of the box. This procedure gives you reasonable assurance that you can install the unit in the gas tank and proceed to install the assembly in the car.

I'll usually fill the tank about 5 gallons at a time after that, to see if the gauge tracks. Capacity is 19 gallons.

[Rob Peters]

12 hours ago, jft69z said:

There really is no adjustment. The new sending unit should be 0-90 ohms thru its span. I'd recommend hooking it up externally first, like you did with the decade box, but with the sending unit instead. Run it thru its range and see if the gas gauge tracks accordingly. 

I usually check the sending unit first with an ohmmeter though, to make sure it had a good, even reading when moving the arm thru its full travel. I've seen bad ones right out of the box. This procedure gives you reasonable assurance that you can install the unit in the gas tank and proceed to install the assembly in the car.

I'll usually fill the tank about 5 gallons at a time after that, to see if the gauge tracks. Capacity is 19 gallons.

Joe, the adjustment I am referring to is what I have read on line and here on the site where members have had to drop the tank multiple times and adjust it by bending the float arm. 

I do agree with you that using an meter to check the ohms on a new one to insure that the range on a new one, when you move the float arm through its full travel,  should produce an ohms readings from 0 (zero) to about 90 ohms

[72 Monte Carlo]

Rob, awesome detailed troubleshooting information! 

[jft69z]

57 minutes ago, Rob Peters said:

Joe, the adjustment I am referring to is what I have read on line and here on the site where members have had to drop the tank multiple times and adjust it by bending the float arm. 

I do agree with you that using an meter to check the ohms on a new one to insure that the range on a new one, when you move the float arm through its full travel,  should produce an ohms readings from 0 (zero) to about 90 ohms

Yeah, I see people doing that, but keep in mind, the tank is odd shaped, so the measurement may not be linear. The arm has that bend in it to possibly compensate for the odd shape. Fill it up 4.5 gallons at a time, see where the needle goes, and drive it.

You could also measure the float travel, and the depth of the tank flange to the bottom, see what you get, but again, the tank isn't a square box. 5 gallons from empty isn't going to be the same measurement as the last 5 gallons to full.

[cny first gen 71]

Yes sometimes the float arm has to be bent as in my case. The unit checked out just fine and I had it hooked to the gauge and took it through the different levels and it worked fine with 1/4 tank it read fine also but when I filled it up after it only went to about 1/2 tank when completely full. Next time it comes out in going to test it on the ground with 1/4 then 1/2 then 3/4 then full. I'm tired of taking the tank out of this thing but I'm getting good at it 😅

[Rob Peters]

4 hours ago, jft69z said:

Yeah, I see people doing that, but keep in mind, the tank is odd shaped, so the measurement may not be linear. The arm has that bend in it to possibly compensate for the odd shape. Fill it up 4.5 gallons at a time, see where the needle goes, and drive it.

You could also measure the float travel, and the depth of the tank flange to the bottom, see what you get, but again, the tank isn't a square box. 5 gallons from empty isn't going to be the same measurement as the last 5 gallons to full.

Yes, clearly that is the case.  Most GM cars I have ever had, including my original Monte and the one I have now (when the gauge was registering properly, on a completely full tank, where the needle is pegged to the "F" mark, while driving it seems to take a long time before you will see the needle move.  So with that said the miles you will get from a Full tank to a 1/2 full tank will usually be a longer distance than the miles from 1/2 Full to Empty.

rob

[Rob Peters]

So, yesterday I was talking to Dennis T regarding trying to see if the float would have full movement up and down prior to putting the tank back into the car and without putting any gas into it.  After all, I said, how am I going to get the float to move up and down from fully down to fully up.

Dennis suggested maybe feeding a piano wire through the fuel line tube and then moving the float up and down using the piano wire but neither one of us knows if that will work.  Laying in bed last night, I was wondering if maybe once the sender is properly mounted inside the tank and with the tank positioned in the proper angle it would sit if installed in the car I can take an ohm measurement and if it is near "0" (zero) I will know it is sitting at the bottom of the tank.  But how will I check if the float are will move to its full up (full) position.  I may have that figured out.  with an ohm meter connected to it why not turn the tank 180 degrees which would allow the float to move to its fully up position inside the tank and if the ohms read 80 to 90 ohms it may be good.

The only thing the idea of doing it this way is I wouldn't know if the float is touching the top of the tank and if that was the case I still would not ow when the tank is full.

Now, again, on the bright side, I will will be able to see if there is a build sheet for my car on top of the  tank.

rob

[cny first gen 71]

I had the tank sitting on the floor blocked up so it was sitting similar to the way it is when it's installed in car. I used a small level on side lip to get angle correct. 

[jft69z]

The sending unit should have mechanical stops built right on the rheostat case to limit travel. It should never get to the point where it hits the top of the gas tank.

If the top of the float exceeds the plane of the mounting flange when you move it to 'full' position, your float arm is bent out of shape.

[Leghome]

You could always get an indescope and look inside the tank before removal and see where the float is sitting on empty and how far it is off the bottom of the tank. When I was having trouble  with my 350 before getting my new heads I looked inside of the cylinders to see the bottom of the valves and heads and also looked down the intake to see the valves inside of the head that gave a decent idea the condition of where everything stood. Attached is a photo of the worst valve before I removed the head. This indescope only cost me like $30 and uses my cell phone/tablet for a screen. As you can see the valve is in really roiugh shape one of the handiest tools I have bought in a wile as I have used it several times aroiund here for other potential problems

 

[Rob Peters]

2 hours ago, Leghome said:

You could always get an indescope and look inside the tank before removal and see where the float is sitting on empty and how far it is off the bottom of the tank. When I was having trouble  with my 350 before getting my new heads I looked inside of the cylinders to see the bottom of the valves and heads and also looked down the intake to see the valves inside of the head that gave a decent idea the condition of where everything stood. Attached is a photo of the worst valve before I removed the head. This indescope only cost me like $30 and uses my cell phone/tablet for a screen. As you can see the valve is in really roiugh shape one of the handiest tools I have bought in a wile as I have used it several times aroiund here for other potential problems

 

Larry, I was thinking about that but I didn't know if, with the baffles that are in there if the  scope would access the area of the float.  

That said, I am scheduled for a colonoscopy on Monday, maybe I can borrow one of their scopes to stick down there, of course it would need to be cleaned up before I would stick that crappy thing into my gas tank.

rob