Tom, thanks for this...now I understand more. I certainly *thought* the gauge needle should be floating/moving a bit while driving, but got confused with all the talk of pegging at 3 being normal, but now I see how/when that is so.
Great stuff...
Caitlin
Santa Fe
--- In diesel_mercedes@yahoogroups.com, audiolaw@... wrote:
>
> Caitlin,
>
> NO! This is not right. The guage, if working properly, should not
> show ANY oil pressure until the engine is running.
>
> While the engine is running, the gauge should fluctuate, depending on
> engine speed. At any speed above 'idle' the gauge should be pegged at the
> "3" mark. At 'idle' it can safely drop below "2".
>
> Remember that what your are looking at is an indication (I hesitate to
> call it a 'measure') of oil pressure. There is NO oil pressure while the
> engine isn't running. Oil pressure builds because an oil pump IN the
> engine is pumping.
>
> So, you have established something - that the gauge itself may be
> working. But you still haven't sorted out the signal to the guage. It may be
> that the sensor is faulty, thereby giving you a bad reading all the time.
>
> A junk yard sensor is the cheap and easy way to experiment with
> alternatives. This is not high tech - all that's happening is a simple circuit
> that allows current to deflect a standard gauge mechanism. So you need to
> figure out the source of the signal variation.
>
> I'm at the office and not near any reference books. But my simple
> minded thought is that the gauge gets 12vdc from the binnacle module, and the
> sensor in the engine provides a variable resistance to ground. So when
> there is no continuity, you get a "zero" reading. With increasing pressure,
> there is decreasing resistance in the engine sensor, this allows current
> flow and that causes the gauge to deflect. When pressure is high enough to
> provide zero resistance in the sender, the gauge will be at full deflection
> ("3").
>
> This means that if the sensor shorts out, the gauge will read at full
> deflect as soon as power is available in the binnacle (when you turn the
> key to position 1).
>
> If I am right, you can pull a sensor out of a junker and measure it
> with an ohm meter. If the ohm meter shows resistance from contact to case,
> then drop it in your pocket and try it out when you get home. (Don't forget
> to tell the cashier at checkout that it is in your pocket - and pay for
> it.)
>
> Tom
>
>
>
>
>
> In a message dated 11/17/2011 5:23:28 P.M. Pacific Standard Time,
> tinymachine@... writes:
>
>
>
>
> Ok folks, I *think* the gauge is all set but I'm not sure what the correct
> readings are even despite the recent discussion.
>
> I cleaned and pried apart the little plastic part that holds the connector
> pin that makes contact between the wire and the sensor. I cut and
> re-stripped the end of the wire, wrapped it around the pin and closed up the
> housing (I did this twice...wasn't sure the first time "held") and pushed it back
> onto the sensor.
>
> With the key out and car off, gauge now reads "0" (though sometimes I have
> to tap the cluster to get it to drop) and as soon as key is in the first
> position it pegs up beyond the "3".
>
> It stays there the entire time I'm driving and doesn't move (I tapped to
> make sure), even at "hot idle" if hot is around 80-85c.
>
> When I turn off the car, needle drops to "0"...though as I said sometimes
> it sticks and a tap will drop it.
>
> Is this a fairly normal oil pressure reading? Can I test this?
>
> Thanks!
> Caitlin
> Santa Fe
>
> --- In _diesel_mercedes@yahoogroups.com_
> (mailto:diesel_mercedes@yahoogroups.com) , "Nate" <vwnate1@> wrote:
> >
> >
> > O.K. :
> >
> > A _brown_ wire , anywhere in the car , is a _GROUND_ wire and so *must*
> be well connected , no loose parts , frayed or broken strands , no
> corrosion permitted or things won't work right .
> >
> > The loose oil sender wire you posted a pic of , is prolly the fault ,
> stick a pin in the open end of the wire and ground it well , turn on the key
> , if the gauge now reads zero , you've found the fault , gently pry open
> the plastic connector and re attach the wire .
> >
> > The oddly worn regulator brushes were because the DPO/DPM wasn't careful
> to hold the assembly in place as they re installed the two screws holding
> it in , so one brush was riding off the edge of the slip ring .
> >
> > You didn't show a picture of the other side of it , it *MUST* say
> > " BOSCH " or it WILL NOT CHARGE ENOUGH .
> >
> > Period .
> >
> > Don't test the top end speed of the car until the tires , suspension &
> brakes are all tip top and then , only when no other traffic is about as
> things happen -REALLY- quickly at high speeds...
> >
> > I chicken out a little over 100 MPH , I only did that a few times to de
> - carbon my engine , it's safer and less nerve wracking to do Diesel Purges
> & routine tune ups...
> >
> > -Nate
> > Caitlin wrote:
> > >
> > > I confirmed that indeed the gauge is stuck as high as it goes when the
> cluster is merely plugged in (no key in ignition, car obvi not running,
> etc) at all times.
> > >
> > > I'm not totally sure what to look for other than brown wires that have
> "loose connections" and tighten them...and maybe bare wires too...
> > >
> > > My electrical gremlin count is growing and I still haven't even
> found/fixed one...(ok, that's cuz I'm sort of avoiding them)
> > >
> > > Good to know I can shoot for 130MPH ;) despite what the speedo
> says...but the one that goes higher was orig to the car and at least i have a
> spare for if/when I send out mine for repair.
> > >
> > > Gonna go check the voltage regulator (as suggested) and also see if I
> can't rejuvenate my hazard switch in hopes of restoring signals (they
> light, inside and out, but don't blink). While after the hazard, I hope to check
> and dig around in the wiring behind the console in hopes of finding
> gremmies.
> > >
> > > Caitlin
> > > Santa Fe
> > >
> > >
> >
>
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