[alfa] Oil Pressure gauge

[Jon Pike <jhpike@xxxxxxx>]

Hi Dave..

Hmmm,  so you've checked the actual pressure with another gauge,  
good...  and you've replaced the pressure sender,  good..  but still 
have the problem,  and still erratic to boot.

I'd check the connections to the gauge and everywhere else along the 
path of power to gauge to sender to ground.  Could be that you have a 
bad one somwhere,  and you're getting flutctuating voltage drops that 
would cause exactly these symptoms.  Erratic would suggest a loose 
connection, too.

A good thing to do would be to get a voltmeter and start measuring 
around while wiggling wires.  I'd guess you should see a steady 12-14v 
(whatever the car system voltage is) at one side of the gauge,  and a 
lower varying one (as the pressure changes) between the sensor and the 
gauge. 
Anyone out there know what the "good" voltages are at the gauge, or 
voltages that give a particular  readings at certain pressures?  For 
that matter, how about resistances over pressure for the sensor itself?

If I had a running car handy,  I'd go measure at a few pressures for you..

Good luck..

Jon and Marcia
77 Spider
Irvine CA


> Dear Alfisti -
> I could use some help diagnosing an oil pressure gauge problem on my 87
> Spider.
> Yeah, those things.
> It reads all over the map - sometimes below 0, sometimes (just a minute
> later) about 20, then back to 0, etc.  It used to be always about 87 until a
> year ago when it first started acting up by suddenly starting to read
> extremely high - almost pegged.  But then I replaced the sending unit (IAP
> part) and it's still crazy, now reading only low numbers, that are never the
> same.
> A while ago I temporarily T'ed into the idiot light a mechanical gauge and
> read pressure about 80 psi, the idiot light never comes on, the temp is
> good, the engine sounds okay, and its been driven for months like this
> without self-destructing, so it would seem that the actual oil pressure is
> "okay".  But seeing low, fluctuating numbers on the gauge is a bit
> disconcerting.  The fluctuations make me think that there is an intermittent
> electric connection somewhere and all I need do is to clean it, but the book
> isn't too helpful in identifying where the connections might be.
>
> Anybody have any suggestions?
>
> Dave Martin
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