[T3] '73 Idle Test

William Jahn willjahn975 at gmail.com
Mon Aug 26 10:54:01 PDT 2019

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 .

On Mon, Aug 26, 2019 at 9:24 AM Jim Adney <jadney at vwtype3.org> wrote:

> William,
> The only other thing I can think to suggest at this time would be to check
> to
> make sure you have the E brain ending in 048 to work with your '73 FI
> system. The E brain ending in 028 was only for '72.
> You've probably already done this, but make sure the TPS is correctly
> adjusted.
> Yes, it's difficult/impossible to find things that are only intermittent
> while
> running, due to vibration or temperature variation.
> However, the bottom line here is that the car drives fine and gets
> appropriate
> gas mileage. It may be annoying that you can't explain the behavior, but
> you
> have to admit that it's not really a problem.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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