[T3] '73 Idle Test

William Jahn willjahn975 at gmail.com
Tue Aug 27 16:20:54 PDT 2019

Jim I haven't had a chance to look at these connections. I do recall in
2009 checking the voltage on the ECU plug not connected and read 12 volts
don't recall reading battery voltage. In order to read an actual voltage
drop as you know you have to have a load which I didn't . I don't know what
the ECU draws yet I assume enough that even a 1 volt drop would affect the
entire system . First I will inspect the wires and connectors you mentioned
and make sure they are good  and that the cold start is not on without
cranking. I will also check the power relay for a voltage drop. No point in
not covering all bases. When I was a ford tech I used to now since I don't
work on cars 5 days a week for a good long time I have forgotten the small
things that create big issues. I was the only one at all the ford
dealerships I worked at since 1970 who could narrow down an electrical
issue just looking at the wiring diagram yet those car/trucks were not over
40 years old . Some were and the new techs had no idea how anything worked
so I'd get to old heap . This is the only FI car I ever owned , I knew how
the newer cars worked with FI yet are much different than these as they
stored info and had a lot more control and of course we had meters we could
plug in to read what was going on. I guess that's why I forget to check
certain things , simple system with 40 years of never checked connections.

On Tue, Aug 27, 2019 at 7:15 AM Jim Adney <jadney at vwtype3.org> wrote:

> William,
> I note that 2 of your observations seem to point in opposite directions.
> Unplugging the air temp sensor makes the idle settle down, making us think
> that the mixture was lean.
> Using a quarter tank of gas in 20 miles sounds like an extremely rich
> mixture.
> I suggest that you take the car for a long drive, like 100 miles, at
> reasonable
> speeds to see what's really going on. Pick a time of day and a destination
> that avoids heavy traffic so you can stay in 4th gear most of the time.
> Start
> with a full tank fill-up and record your odometer reading. End with the
> same
> and record the end fill-up gallons. Calculate your actual gas mileage.
> (mi/gal = (odo2-odo1)/(gal used)
> Before you do this, here's one more check you can do: There's a wire that
> runs to the temp switch under the IAD. Pull that wire off and measure the
> voltage between that wire and ground. It should be zero with the engine
> off
> or running. It should be 12 V while starting. That's assuming your Cold
> Start
> Valve is plugged in.
> If you get 12 V with the engine off or running, you've got a misconnected
> wire on the starter. Did you have any work done on the starter around the
> time when this problem started? The solenoid terminal on the starter also
> gets a wire to the brain and the Cold Start Valve. If that wire is
> connected to
> the hot terminal on the starter, it will run the system rich all the time,
> even
> with the Cold Start Valve disconnected.
> Do you notice a change in the idle when you connect and disconnect the
> temp switch wire? There should be no change.
> I wonder if you might actually be running rich most of the time. Inspect
> the 2
> wires that carry 12 V power into the FI wiring harness in the LF corner of
> the
> engine compartment. Look for a wire that is frayed, with only a few
> strands
> still connected. Extreme richness could be caused by low system voltage,
> but you've got a new VR, so the VR is not the problem. But a high
> resistance
> in the wires that feed the FI could cause a reduction in the supply
> voltage to
> the FI. I've seen this problem on another car.
> Jim
> On 26 Aug 2019 at 10:54, William Jahn wrote:
> > It has the 048 . The only thing I can add is the gas millage is not very
> > good. Of course most of the driving here is stop and go yet it's been
> like
> > this for a while and it used to get better millage. I can go through a
> 1/4
> > tank in 20 miles .  From the way it acts it seems to start out rich
> because
> > of a high TS2 reading then leans out since the TS2 in my mind drops to
> > fast. This seems to be why connecting TS1 then leans it out more since by
> > now it's temp has risen dropping it's resistance.The reason I feel it's
> > leaned out  on rennlist an old tech trick was to unplug it to richen the
> > mix . My thinking is if I change TS2 with a new none Bosch part since
> Bosch
> > no longer makes these and this part is reading much more in line with
> what
> > it should perhaps it won't start out at such a high resistance then nose
> > dive to 77.5 ohm in 2 minutes then it just might allow TS1 to be more in
> > line and works as it should since TS1 seems to work proper. I just don't
> > feel running to lean is a good idea. I drives ok with TS1 connected and
> > unconnected because it has a load I can't feel it. Yet if I try to  read
> > charging system out put it's next to impossible to get a steady RPM
> reading
> > with TS1 connected it causes the RPM's to rise and fall a few hundred rpm
> > all while holding the throttle steady  from  idle to 2300 RPM then above
> > that it does read steady. This is also what I hear and feel even at idle
> > and raising it standing at the rear of the car I feel this what I call
> > erratic miss hand by exhaust tip and hear this slight skipping as one
> would
> > hear a miss fire.
> >
> >   This is what I found looking further .
> >
> > "
> > *Q: What is the effect of disconnecting the TS1 sensor? A:* The TS1
> sensor
> > produces a fairly weak effect on the mixture, to compensate for the
> varying
> > density of air with temperature. Removing the sensor will slightly richen
> > the mixture. This is a common mechanics "trick" for an old engine that is
> > running lean due to wear or vacuum leaks. See the PL analysis above for a
> > detailed explanation.
> >
> > I measured the effect of a disconnected TS1 sensor (see the question
> above
> > for the setup conditions). Disconnecting the sensor increased the
> injection
> > pulse width to 7.1 ms - an 11% increase, almost exactly what the analysis
> > of this effect predicted (see the PL analysis section). Note that this
> > enrichment effect is variable as the temperature changes - stronger for
> hot
> > temperatures, weaker for cold - due to the elimination of the
> compensation
> > for air density as a function of temperature."        I found this here .
> > https://members.rennlist.com/pbanders/ecu.htm#ICM
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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