[urq] reference sensor bench testing

Peter audionly at gmail.com
Sat Aug 29 19:19:05 PDT 2009


Dennis had been driving his car for over a year when this happened. He
stopped at a convenience store and came out and the car wouldn't start. The
first thing I did was make sure the pin was there. Then hooked the sensor
back up and hooked an ohm meter to it and turned the car over..........No
reading on the ohm meter. Then I pulled the sensor out of the block and ran
a screwdriver back and forth across the face and the ohm meter moved.  Then
we tried another known good sensor with the same results. Next we had heard
of a issue where the sensor loses some of it's magnetism and to measure the
distance from the sensor to the pin with some modeling clay. No issue there.
Then we plugged the sensor back into the harness but left it out of the
block. I ran a screwdriver rapidly across the face of the sensor while
Dennis cranked the car............... It started. (No one had ever heard of
doing this but it does make sense once you analyse it. The computer is
looking for an exact pulse from the hall generator and the reference sensor.
It therefore doesn't make a difference if there are a hundered pulses from
the reference sensor; as long as one pulse matches the hall generator.  We
couldn't figure out why we couldn't get a reading with the ohm meter when we
installed the sensor in the block but could when we ran a screwdriver across
it. Then Davey Jones suggested using a scope instead of an ohm meter. It
picked up the signal from the sensor. Now, knowing that was OK; we thought
there must be a break in the harness between the sensor and the ECU. Brendon
Rudak of Apikol and Steve Eiche of Shadetree hooked the scope up to the ECU
pins and it showed a signal both from the reference sensor and the hall
generator. What it also showed was that even though we knew both the
distributor and the flywheel mark were exactly lined up; the signals from
each respective one was happening at a different time. We moved the
distributor up a little and the car immediately fired and ran. The ECU for
the 20V and the WX for this function is the same.   Regards, Peter

On Sat, Aug 29, 2009 at 5:55 PM, Mike Del Tergo <mdeltergo at hotmail.com>wrote:

> Peter,
> not sure on the 20V if there is an insitu test for the sensor but there is
> for the UrQ and it failed that. I Ohmed it and it is about 110 Ohms off a
> similar MC sensor, 850 vs the MC 970.  I'd consider both pretty close to the
> 1,000 Ingo referred to. (the MC unit is physically much shorter and has a
> slightly bigger in diameter, I'd guess you could shim an UrQ unit to work in
> later cars, but not vice versa)    I'll go back to the car when I can and
> ohm the "good" speed sensor.  Your 20V experience seems like it may be the
> first fire up after a transplant?  My car was running one minute and
> wouldn't start literally a minute later.  As many tbelts go/skip on start
> that is entirely plausible as I have not yet physically checked TDC marks
> but will when I can have someone with experience help.  Alterantively I
> tried to swap the speed sensor over (as they are the same) but didn't have
> the necessary tool to get a got grip on it to pull out.  (the car broke
> down at an intown parking garage)  At least it is free moving and won't
> present the issues Louis Alain had!
> Mike
>
> ------------------------------
> Date: Sat, 29 Aug 2009 17:26:16 -0600
> Subject: Re: [urq] reference sensor bench testing
> From: audionly at gmail.com
> To: mdeltergo at hotmail.com
> CC: ingo.rautenberg at gmail.com; urq at audifans.com
>
>
> The pin moves a magnet in the sensor. An ohm meter won't pick up the signal
> of the pin. You need a scope to see the differential. Make sure you get one
> to do the testing before you go any further. I/we have been down this road
> before with Dennis Graber's 20V. After everything was said and done we found
> that somewhere between the flywheel mark (through the crank, through the
> crank timing gear, through the timing belt, through the cam ) to the timing
> mark on the distributor had lost 3 or 4 degrees even though the marks said
> both were on top dead center.  We kept thinking it was the reference sensor
> because of the readings. We eventually advanced the distributor a couple of
> degrees and the car fired right up. As we speak; Dennis is trying to find
> out where the slip happened.
>
> Regards,
>
> Peter
>
>
>
> On Sat, Aug 29, 2009 at 5:08 PM, Mike Del Tergo <mdeltergo at hotmail.com>wrote:
>
>
> Ingo,
>
> I had thought that the reference pin swinging by generated and electrical
> field of some measurable output and thought there might be another way to
> generate a field and measure.  I will Ohm the unit for starters.
>
> Thx
>
> Mike
>
> > To: mdeltergo at hotmail.com; urq-bounces at audifans.com; urq at audifans.com
> > Subject: Re: [urq] reference sensor bench testing
> > From: ingo.rautenberg at gmail.com
> > Date: Sat, 29 Aug 2009 22:02:19 +0000
> >
> > It's basically the same for as for the V8, 5ktq, etc.
> >
> > I forget the order, but there are 3 pins in the connector and the center
> pin -- when connected to one of the side pins with a multimeter should ohm
> out to 1k ohm. If it doesn't, it's bad. Sometimes the sensor can be flaky at
> only higher temps, so this method really only works to tell you if you have
> an absolutely dead sensor.
> >
> > HTH
> >
> >
> > Ingo Rautenberg
> >
> > -----Original Message-----
> > From: Mike Del Tergo <mdeltergo at hotmail.com>
> >
> > Date: Sat, 29 Aug 2009 21:49:22
> > To: <urq at audifans.com>
> > Subject: [urq] reference sensor bench testing
> >
> >
> >
> > Has anyone run across a way to bench test the flywheel reference sensors
> Audi uses? One in my UrQ tests bad through the harness but of course it is
> not unheard of to lose the reference pin so I wanted to bench test before
> ponying up for OEM.
> > Mike
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