[T3] '73 Idle Test

William Jahn willjahn975 at gmail.com
Sat Aug 31 18:58:27 PDT 2019

Jim how did you come up with the voltage drop? I only have two values the
resistance and the voltage , with ohm's law I just get current.

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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