[T3] '73 Idle Test

William Jahn willjahn975 at gmail.com
Sat Aug 31 16:24:52 PDT 2019


Jim when I read resistance on #30 & #87 I had both wires disconnected .
What I saw was it was jumping around and I didn't record the resistance I
do recall seeing above 25 ohms and the lowest was 9 ohms. If I turned the
key off then on again it did the same thing I was mistaken with the 47 ohm
that was from the TS2. When I did the voltage drop test it was in mA on
both #30 & #87 yet it was not steady either. Neither of my DVOM's have a
high low so I could capture the high  low readings  they just have hold.
Once I took the cover off and manually closed the contacts keeping my hands
clear of the probes so not to introduce resistance I still got no lower
than 9.5 ohms and still was higher than 20 ohms just holding the contacts
closed , I found that odd how the resistance would vary not moving the
contacts and with no voltage or current to heat the contacts. Once I
cleaned them testing by hand and in the car with the coil energized it was
a consistent 0.02 ohm , I didn't try the voltage drop again after cleaning
the contacts. My DVOM with the probes touching  would always show 0.00 ohm
in auto range I always test so I can subtract any probe to probe reading. I
never try to read resistance in a live circuit and current readings I break
the circuit meter is in series than I start at the 10 amp if it's far less
then switch to mA . I didn't check current draw through the relay , I could
have gone in series between #30 lead and #30 relay same with #30 connected
and done the same with #87 at least I would know just what the FI draws
while running . This also may have shown different current draw on both and
told me if the contacts had an issue .

 I didn't have good results with both temps sensors connected , I may just
pull the ECU and still connected engine running see what the voltage is off
the power relay . Then pull the connector and check to each component for
resistance to the temps sensors and injectors and see if I can move /wiggle
wires to see if I can find an intermittent . Then the ECU grounds and
perhaps with every wire unplugged see if any two wires have continuity ,
the grounds should have but not any of the voltage feeds or the MPS even
the TPS on the TPS I can leave it connected and see if it reads the same as
testing at the TPS unplugged.

 I know it's a lot of testing yet I need to know if anything in the wiring
is causing this .

On Sat, Aug 31, 2019 at 2:38 PM Jim Adney <jadney at vwtype3.org> wrote:

> On 30 Aug 2019 at 12:59, William Jahn wrote:
>
> > I always thought because I've done voltage drops before if I connected
> > the voltmeter to batt poss and then probed the relay connected so it
> > has current flow I would read batt voltage at both #30 & #87
>
> Yes, looking for excessive voltage drops is a reasonable thing to do, and
> it
> looks like you found a problem in your relay. I don't understand how you
> got
> a measurement of 47 Ohms, as that's so high that the system should not
> have run at all, so I don't believe it. At 47 Ohms, you'd have a voltage
> drop
> of 47 Volts in a system that only has 12-14 Volts to start with.
>
> I wonder if you were trying to read resistance with the circuit live,
> which can
> lead to extremely misleading results.
>
> > I did this without the engine runner just key on and #30 read 0 mA
> > telling me the wire was good no drop yet #87 read 2 volts less less
> > than battery voltage which would the the resistance in the relay
> > contacts. .
>
> After I sent my last message I realized that I was wrong about this being
> only
> possible with the engine running. That would be true for the fuel pump
> relay
> but not for the main FI power relay. Doing this with the key simply ON was
> the right way to do it.
>
> Tests like this, should be done in Volts mode, not current or resistance
> mode. In current mode, if you find a bad connection, you're likely to
> damage
> your meter. In resistance mode, the extra voltage drop created by the
> external current will give a wrong reading, and the reading will be
> negative
> (negative resistance!) with the probes in one of the two possible
> positions.
>
> I still recommend trying a road test, with both temp sensors connected
> properly. It's impossible to go by the gas gauge, because the FI gas gauge
> readings are misleading. The 1st quarter tank is MUCH bigger than the last.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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