Fuel gauge

[Bob Claffie]

Just put in a new fuel sender in my BN6 and with the tank empty the gauge reads full! Bad sender, bad gauge, or hooked up backwards?? Gauge not hooked up when I bought the car. Replaced the sender as the original had a hole in the float. Bob

 

[Keoke]

HI Bob, if the guage is the correct one for the car I think you obtained the wrong sender.---Keoke??


HEY Bob, did you keep the old sender? .If so and it is good the hole will not affect its performance if the tank is empty. why not hook it up and see what happens to the guage?,

 

[Dave Russell]

Hi Bob,
If the dash part of the gage is connected properly, a quick check of the panel gage is to remove the wire connection to the sender at the sender end. With no connection to this wire, the gage should read somewhere around full. With this same wire grounded the gage should read empty.

With the tank empty or the sender float down, & it's wire disconnected, the gage sender should read near zero ohms when checked with an ohmeter connected from the sender terminal to ground. With the float up the ohmeter should read around 70 ohms. Note: the sender ohm readings could actually vary from 70 ohms to about 90 ohms with the float up & from around 10 ohms to zero with the float down.

Make sure that both the dash gage case & the sender case have "good" ground wire connections. A poor ground on the gage case can result in a gage that reads about 30% low. A poor ground at the sender can cause erratic gage readings. Not that they don't bounce around anyway as fuel sloshes around in the tank.
If the wire between gage & sender is open or not making connection the dash gage will always read full. if this wire was grounded somewhere along the line, the gage would always read empty.You could try a temporary wire from gage to sender. If the sender check shows opposite to these readings, you have the wrong sender.

You can do these checks with the sender removed & just raise/lower the float arm. You do need a temporary jumper from the sender housing to ground for the test.

When installing the sender, make sure that the sender to tank gasket is in good condition & sealed, the top lid on the sender is sealed, & that the sender hold down screws are sealed & have copper washers under the heads. Lot of places for leaks & the resulting gas fumes in the boot.
D

 

[anthony7777]

bob claffie,when i bought my car this past may the fuel guage indicated the tank was near full all the time no matter how much fuel was in the tank,the po.had installed the sender in backwards,seamed to be the simplest place to start.easy fix.

 

[Bob Claffie]

Anthomy, do you mean the float faced the wrong way? My float faces toward the front of the car.
Dave, I will try the fixes you suggested , but as far as grounding the sender, is it grounded through the mounting screws? There is rubber under the tank and I have a section of rubber/ neoprene tubing in the fuel line so the tank may not be grounded correctly. Can / should I run a seperate ground from one of the mounting screws?? Thanks, Bob

 

[Dave Russell]

Hi Bob,
Yes - I would run a separate ground.

I'm not Anthony but I've tried the float both ways - float to the front & to the back. On my particular tank it makes very little difference. On your tank I would try it toward the back to see what happens. I've heard tell that they were originally mounted with the float to the rear.
D

 

[Keoke]

HI BOB, I have in the past always recommended that a positive ground be run from the sender to the cars chassis to circumvent the case where the fuel line gets cut and rubber hose is installed. Not that the fuel line is intended to act as a positive ground.The fact that it does is incidental and not intensional. To add the ground I suggest not using the sender mounting screws but one on the cover near the guage's connection.---Fwiw---Keoke

 

[anthony7777]

hi bob,evidently there must be a differance in float configuration between your bn4,and my bj7 because the float in my tank must face forward in order to give a correct reading so your probably looking at a wiring issue.anthony bj7 3000 M.K.II /ubbthreads/images/graemlins/hammer.gifi just checked moss site under fuel tanks sender unit,they show all from 100-3000 use the same one,pict.shows float ass. facing fwd.

 

[dklawson]

I've watched this thread and questioned whether or not I could/should add to it.

Not knowing the model year evolution of Healeys, I can only make a couple of suggestions in passing. As a couple of you may have read on a similar thread in the Spridget part of this board, BMC started implementing the gauge voltage stabilizer to its cars during 1964. Prior to that the fuel gauges ran on full battery voltage and were of the "balanced magnet", fast response type. The balanced magnet fuel gauges used sending units that operated from low-ohms=empty to high-ohms=full. Once the stabilizer was added, the sending units operated the other way, high-ohms=empty to low-ohms=full. You can't mix the senders and gauges.

Again, I don't know the evolution of the various Healey models so forgive me if none of this information applies.

In closing, don't throw out your old sender if its windings still work. Brass floats can be soldered to repair pin holes. If you have a plastic float, these too can be repaired by using a small soldering iron to remelt the plastic around the pin hole or crack. Of course, both repairs should only be attempted with electric irons once you have gotten the trapped fuel out of the float.

 

[Dave Russell]

[ QUOTE ]
Again, I don't know the evolution of the various Healey models so forgive me if none of this information applies.
In closing, don't throw out your old sender if its windings still work. Brass floats can be soldered to repair pin holes. If you have a plastic float, these too can be repaired by using a small soldering iron to remelt the plastic around the pin hole or crack. Of course, both repairs should only be attempted with electric irons once you have gotten the trapped fuel out of the float.

[/ QUOTE ]
Hi Doug,
To my knowledge, the "Big Healeys" always used the magnetic fuel gage. The BJ8's were slightly different. The gage's one redeeming feature was that it did not require a voltage stabilizer to compensate for varying supply voltages. Maybe the attached schematic will explain some of the strange workings of the gage. The coils in the dash unit are adjustable for position-magnetic gap so they can actually be made to be fairly accurate with enough adjusting. See attached.
D

 

[dklawson]

Thanks for the schematic Dave, it's a very good illustration. I'm already familiar with that family of instruments.

I only suggested this as a possibility as the description was for a reverse acting gauge. However, if big Healeys never had the voltage stabilizer then there should only be one type of sending unit. I hope my previous post didn't confuse the situation... I tried to offer it with a caveat.

 

[Bob Claffie]

You guys are doing a bang up job educating me on the inner workings of the fue system. I hope this is the last flog of this dying horse-- my gauge doesn't have any legible markings on it. What is the orientation of the two connections, either from the drivers seat or from the back of the gauge. I have this fear that the PO had it connected wrong (with a new harness installed) but never tested. Thanks, Bob
I did put in the separate ground today, but now have the complete dash disassembled and out of the car.

 

[Dave Russell]

Hi Bob,
Rear view, connection to sender on the left, connection to supply is on the right & might have two wires.
D.

 

[Keoke]

Yeah Anthony, they face towards the front of the ca.However, as far as accuracy goes they are similar to the old Jag electric clocks. That is they are reliable when the tank is bone dry or it is full to the brim.Jag clocks likewise are accurate twice a day too.---Keoke- /ubbthreads/images/graemlins/laugh.gif

 

[anthony7777]

keoke,with material like that,you should be working VEGAS. /ubbthreads/images/graemlins/jester.gifbut seriously folks,mine only worked correctly in the fwd.position. /ubbthreads/images/graemlins/hammer.gif