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Re: Fuel sending unit resistance values.

To: mgs@autox.team.net
Subject: Re: Fuel sending unit resistance values.
From: "John M. Trindle" <jtrindle@tsquare.com>
Date: Tue, 18 Jul 1995 10:35:09 -0400 (EDT)
On Mon, 17 Jul 1995, Mark Jurras wrote:

> adjustable if you must. Because of the design there is much variation
> from stabilizer to stabilizer.
> 
> > but 1) why?  The stabilizer is a pretty sturdy component.. 
> 
> Is it??
>
On the order of a turn signal flasher I would suspect.  Not as sturdy as 
a transistorized one (in terms of cycles) but less sensitive to 
environment perhaps.
 
> > Anyway, the hard part is figuring out the steady-voltage equivalent.
> 
> It is pretty straight forward. You start the car and connect a
> voltmeter to the output of a working stabilizer and the needle
> indicates the steady voltage equivalent. (The digits display the steady
> voltage equivalent if you have one of them new fangled digital Volt
> meters)
> 
Must be pretty fancy.  On our el-cheapo Rad Shack digital ones it says 
"0" and "10.5" and whatever other number it decides on.  Setting to AC 
does NOT work.  The swing needle meters bounce around.  See... the 
frequency is pretty slow (< 3 Hz?).  The tech article posted to the list 
included a circuit to integrate the waveform over time.

> Even if you if you were off by 0.4V that is only a 4% error. 240 RPM
> error on the tach at 6000 RPM, 1/25 of a tank on the fuel gage, 8
> degrees on the temp gage (if it is electric) at 190, 3 lbs on the oil
> pressure (also if electric). Do you think any of these gages are that
> accurate to begin with??
> 

Luckily the tach is not >supposed< to run off of chopped voltage... it 
has a "steady" 12v input and the pulse from the distributor/coil/module 
to deal with.  I threw the tach in for comic effect (I did this once, the 
needle bounces like crazy).

It's the temperature gauge I am worried about most.  The fuel gauge can 
be off if it is at least consistant and the oil pressure gauge is mechanical.
True, 4% isn't much but the tech article suggested the level is more like 
6v, not 10v! 

Anyway, I'm leaving mine in.  Now that I know how it works it's part of 
the funky charm of driving an old britcar.

John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP     | '69 Spitfire E Stock | '88 RX-7 C Stock
Home Page:  http://www.widomaker.com/~trindle
"Sometimes there's not enough rocks - Forrest Gump"


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