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MG MGA - Fuel Gauge Flicker
|Not that I have my generator charging I wanted to make sure that all the gauges are working properly. |
I notice now that as soon as I turn the key (and also with the engine on) that the fuel gauge flickers to zero for a microsecond every second. The rest of the time it does read the right amount of fuel.
The movement of the needle is not dependent on engine revs or on the electrical loads (i.e. brake lights or head lights).
I have read full Barney's pages on how the fuel sender and gauge should work, however in this case the fuel gauge works but it seem like there must be a cyclic current peak from time to time which reaches the 'empty side solenoid' causing the needle to flick back to zero for a micro second.
Does any of you know what could be causing this?
I have still not measured voltages across the gauge.
Note however that the PO did install a grounding cable from the Sending unit to the car frame (leaf spring actually) as the metal hoses to the pump were cut an substituted for rubber ones.
I intent to troubleshoot it this weekend. The gauge is functional just this flickering is annoying.
Also a general interest question; I understand there should be a resistor for the gauge; where is it located so I check it? as this could be faulty and changing its resistance with vibration?
|Once per second cyclical flicker of the gauge could be in concert with a slight sloshing of fuel in the tank and resulting small motion of the sender unit. The problem may be an intermittent contact in the sender unit. To check this, disconnect the sender wire (at either end) and install a resistor from the gauge "T" terminal to chassis ground. If the gauge then keeps a constant reading, the fault must be in the sender unit. For resistor value, 0 ohms = Empty; 68-70 ohms = Full; roughly linear in between, so 34-35 ohms = 1/2 on the gauge.|
There is a snap connector in the signal wire near the starter switch. This should not cause a cyclical intermittent connection, but it bears checking anyway.
The next item is just a guess, but a Voltage Stabilizer of the type used in later model MGB would cause a cyclical switching signal on the input power wire. MGA should not have one of these, but it's easy to check. Touch a test light to the "B" terminal on the gauge (green wires), and see if the light pulses on-off. If so, remove the voltage stabilizer.
Grounding on the leaf spring is a bad idea (should be entirely ineffective), as the leaf springs are mounted on rubber bushings (and the shock absorber link has a rubber joint). An added grounding wire on the sender unit can be connected to a tab on the frame just above the rear axle.
For everything you ever need to know about function of the MGA fuel gauge, follow a dozen pages starting here: http://mgaguru.com/mgtech/electric/fg_01.htm
|You may have an intermittent connection at the sender unit. The grounding point at the sender is produced using the pivot point of the float. This connection on my sender was iffy at best. I simply attached a jumper between the float arm and the base of the sender,|
Leaving enough slack in the jumper to allow the float to travel up and down.
|I will follow the instructions and advice given.|
This nice task together with the others I have will keep me busy through the weekend! ;)
|Gonzalo, could the flicker coincide whith the fuel pump energizing? If it does it could be a poor power supply i.e. bad connection somewhere on the ignition switch dependant circuit (#17 and fuse box A4 terminal on the official diagram). Just a thought, Lindsay.|
|Good one Lindsay! The same might happen if the pump and sender are sharing a bad ground point. (not that there could be any of those under the back of an A)|
|Fletcher R Millmore|
|Last night I fixed the flicked. |
As Fletcher and Lindsay predicted it was linked to a poor ground connection at the fuel sender.
Some WD40 and a wire brush did the trick!
I also cleaned the fuse-box contacts , etc.
|How about a gauge that pops the other way, up to "full" every now and then, no rythm to it, just random? Mine just started this the other day.|
|This has me a little confused. If the gauge is flickering to empty momentarily, I would expect to find an intermitent short to ground in the signal lead going to to the gauge -- going to zero resistance (and the "empty" condition). A faulty (or intermittent ground would (I thought) lead to the gauge flicking to "full" as the ground is lost (infinite resistance) -- Steven's problem. What have I missed??|
|F. J. Bruns|
|Guys and Gals,|
I wanted to reopen this subject since I now got around to looking at it properly.
I have still a fuel gauge with reads correctly, but flicks to full randomly and not in sync with the fuel pump.
I started to look at the wiring and as Sir Barney Gaylord suspected I had some sort of voltage regulato in series with the power cable. This is was hooked up onto one of the cables that runs into the terminal A of the voltage regulator.
I took it off, and the car operated in the same way however the fuel flicker is still there, although I think it is less now, but still there.
Any ideas on where else to look? Something that has some sort of cyclic power consumption as soon as you turn on the ignition.
Here is a picture of the device I removed. Maybe you can help me identify it.
Seem like it has been on the car for a long time!
I removed it as I understand the MGA does not need it and is not on the original wiring diagram, but just want to make sure.
That looks like a circuit breaker to me. (12 volt, 30Amps.) It works like a fuse but instead of blowing and remaining blown like a fuse it will open the circuit and then cool off and make contact again, repeating this action until the overload or short is corrected.
|In that case I guess it is better to leave it in place then, as it is a safety feature...right?|
|I found the cause of my guage flicking past full. Months ago I replaced the gasket under the sender unit cover with rubber that I thought was gasoline compatible. Turns out it wasn't and it had bubbled toward the coil in the sender unit and was pushing a wire against one of the contacts. I replaced the gasket and all is well.|
|I need to do some further testing to see what it could be. |
Since the needle flick towards full, my understanding is that the voltage across the 'RH' electromagnet of the gauge must be surging for a Microsecond. I this this can be caused by a momentary short of the fuel sender resistance. Maybe I have the same problem as you Steven.
I was too lazy to take off the sender, but I may have to order a new gasket and bite the bullet.
This thread was discussed between 11/03/2010 and 26/07/2010
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