7 replies to this topic

[matt68]

Hi,

My Fuel gauge sender unit reads 25 Ohms full, and 235 Ohms Empty, which is within the realm of correct.

My fuel Gauge itself (smiths, built into the bottom part of the speedo, centre speedo) will read well above full when the tank is full, full when the tank is half full, and somewhere between half full and 3/4 full when the tank is empty.

I want to check the operation of the voltage stabiliser, and check it is wired correctly. There are no other gauges connected through the stabiliser, only the fuel gauge. (I Have Mechanical temp & oil pressure gauges - aftermarket)

Any ideas?

Thanks.

[miniboo]

what does the gauge do if you disconnect it completely from the tank/sender unit?

[matt68]

If disconnected, the gauge goes to empty (well right back to the needle stop before the 'E').

How do I test the Gauge?

[miniboo]

well i would say that the sender unit is faulty in that case as the gauge is returning to zero.

i think that if you short the two wires together it should go to full.

also does the temp gauge work because if it does then it rules out the voltage regulator being duff

[matt68]

I swapped the sender for a spare sender, the fuel gauge behaved the same.

(I don't have an electrical temp gauge. The car is a 1968 morris deluxe. The fuel gauge is in the bottom part of the speedo, centre speedo type.)

I figure two sender units are unlikely to have the same fault, and also both test at around 20 Ohms full, 240 Ohms empty, so I still feel the problem is with the gauge or the voltage stabiliser.

Or am i just off my tree?

[dklawson]

Your tests are correct and the resistance ranges you measured are correct.

It's frequently not possible to directly read the voltage output of the stabilizer as it's fluctuating on and off, even analog meters may not show the average voltage value correctly. (Did you download the PDF I posted the link to in the other thread on gauges? If not, get a copy of it as you diagnose this.) If the stabilizer is not cycling it will pass full 12V which will make gauges read high. Start by cleaning the mount for your stabilizer. The case is an earth connection and it must have good electrical contact. Run a separate ground/earth wire if necessary. If cleaning the earth connection doesn't fix your situation, try and locate some of the u7810 chips I mention in the PDF article and rig up a quickie set of wires or clips to attach this to the fuel gauge and repeat your test.

The gauge's can get out of calibration but it's not common. I do suspect your stabilizer and/or its ground. The u7810 chip is your least expensive fix.

EDIT: PDF Link
http://home.mindspri...eStabilizer.pdf

Edited by dklawson, 26 July 2006 - 12:20 PM.

[matt68]

Doug (dklawson),

Thank you very much for the article attached, I think it is about as comprehensive as I could hope and I will read it in more depth over the weekend.

Would one of these do the job?

Voltage Stabiliser on ebay

I just wasn't sure if it really would do what it was supposed to.

any ideas?

Cheers
matt68

[dklawson]

The item on eBay should work well.