Re: [DML] Gauge issues

["Michael Conrad" <mike@xxxxxxxxxxx>]

On Wed, 21 Apr 2010 07:36:04 -0400, Jon Lockwood <jn_lockwood@xxxxxxxxx>  
wrote:

> I am having issues with my fuel and oil pressure gauges.  I replaced the  
> fuel sending unit and my gas gauge still reads half full when empty.  My  
> oil pressure reads mid scale when off and peaks out when engine is  
> running.  My question is there a voltage stabilizer in this car that  
> controls the gauges?  I can only assume the voltage is to high.  I am  
> waiting on a service manual, but if anyone has any suggestions I would  
> greatly appreciate it.  Thanks

Not sure about supply voltage, but personal experimentation on my own car  
(and thats the limit of my experience, btw) shows that the fuel sender is  
a variable resistor between 0 (empty) and 85 Ohm (full), and the oil  
pressure is also a resistor at about 1 Ohm per psi.  The temp sender is  
yet another resistor that goes from 4000 Ohm (cold) to 100 Ohm at normal  
temp (220 F).

If you had 40 ohms worth of bad ground connection somewhere, it would  
explain your gauge readings.  (and temp should read a little low but  
wouldn't be as obvious, and the volt gauge would read low, but magnitude  
would depend on how much resistance the gauge exhibits).

 From playing with a volt meter and the wiring harnesses that connect to  
the back of the instrument cluster, it seems that the gauges are supplied  
with plain old + from the battery.  Considering how everything bounces  
when I turn the lights on, I assume it's not any more regulated than the  
rest of the car.  Since all analog measurements are resistors, they likely  
are a fraction of the resistance of the gauge and any voltage should  
create the same amplitude.  (not that I've taken them apart to verify  
that, but they have 3 poles: + - and signal, so I assume thats whats going  
on).

Hope that helps.

-Mike
#5732


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