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Fuel sender specs... inaccurate gauge??

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lesingepsycho

Jedi Warrior
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Hey everybody. I changed all of my Smiths gauges out for Autometer Pro-Comp Ultra-Lites. I absolutely LOVE them and they have saved my engine AT LEAST TWICE (once when my oil plug FELL OUT and once when the car almost boiled over due to air lock)! When I got to the gas gauge ( model 4316 ) I bought the gauge that was the "Universal" model with gauge readings from 240ohm Empty to 33ohm Full. At the same time I installed a new fuel sender in the tank and I also replaced the voltage stabilizer with a solid state unit. Now when I fill up the tank it goes way up past the Full mark and stays up in that area until I've gone about 100 miles and then starts moving toward the Empty side fairly quickly after that and arrives at the Empty mark about the time I assume I'm reaching empty (never pushed my luck though although I thought I had a close call one night PHEW!). My question is, was it possible that I installed the fuel sender in the wrong direction so that the float doesn't drop at the proper rate or was I mistaken about the impedence ranges? Autometer also makes the same gauge with impedence ranges of (E-F) 0-30ohm, 0-90ohm, 16-158ohm, 73-8or12ohm. I haven't been able to find impedence ratings for the Midget sender and I don't know how to test the impedence with a multimeter. I have the old sender in my trunk if there is a way to test the impedence on it (assuming it was working properly) but it has only one terminal on it and I don't know how to test impedence across that one terminal. I'm sure somebody out there is more knowledgeable and I thank you in advance for the help! Cheers!! /ubbthreads/images/graemlins/cheers.gif
 
Lesinqepsycho, hook up the positive side of your ohm meter to your single connection and your gound to the casing and see if that will give you a reading. Wayne
 
Lesinqepsycho,
What year spridget do you have? I ask because they early fuel sender units/guages read opposite of the later units Ohms wise. You also say that you replaced the sending unit with ????. The proper spridget one or Autometer? Don't know about the autometer guage but the spridget guages can be adjusted by moving the small coils inside using the two small nuts on the back. Sounds like this is your problem, i.e., the guage is trying to read the way it should but the Ohms resistance isn't matching. When you installed the 'new' sending unit is the float towards the center (towards the left) of the tank? If it's not that could be part of the problem. Early sender units went from 258 Ohms empty to 14 Ohms full, later sending units go from 30 Ohms empty to 120 Ohms full.
 
Thanks for the reply Biff

I have a 1973 MG Midget and I replaced the fuel tank sender with Moss part# 361-900 which the catalog says is for years 1972 on. I know autometer sells a sending unit but I wasn't sure how it would fit so I figured I would stay with the stock MG sender. For that matter, I wasn't even really sure what direction to mount the new sender in the tank. I don't think it was keyed and so I wasn't sure if it mattered which way it went in as long as it didn't collide with anything, afterall, fluids naturally level themselves. However, I think I installed it with the float towards the back of the car. I'll have to drop the tank and recheck its position to be sure, but it sounds more like my sender is 258-14 and the gauge is on a 240-33 which would explain why it is close but no cigar. Any suggestions on how to make them compatible? I've basically been going off of my tripometer with the fuel gauge as sort of a suggestive backup for good measure. Thanks for the advice. Cheers, /ubbthreads/images/graemlins/cheers.gif
 
Hello LSP,
the original gauge and sender works with a zero ohms at full. I have no idea what the empty reading is, but if you have measured it by now it should give you a figure. If you are lucky enough to have something around 200 ohms at empty, simply put a 33 ohm resistor in series with the sender wire. My guess is that you won't be that lucky.
Ever think of using the stock Smiths gauge?

Alec
 
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