[T3] On my 73 square

William Jahn willjahn975 at gmail.com
Thu Sep 12 16:47:09 PDT 2019

Here's what I checked . I removed the head temp sensor I had in the car.
Both that one and the spare good one I have read very close to the same.

 I checked the spare from the connector to the crimp and did it several
times and got no ohm reading it was open as it should be. I just now
checked the one I had in the car and did it several times, from the
connector to the crimp I read 1.8k ohm , I also checked from the connector
the 1/4" female to the exposed wires that are not touching the crimp and
that was good no resistance. from the crimp to the thread of the temp
sensor I read 16 ohm . I guess there is some issue in the crimp. Not that
changing them made one bit of difference other than it took longer before
connecting the air temp to screw it up.

 I checked the air temp sensor cold 82*F 223 ohm let it run with the engine
cover in place and watched it after 20 minutes I read 108 degrees and the
lowest it got was 125 ohm . I drove once before and it was much hotter and
the low was 107 ohm the IAD temp measured on the area the sensor screws in
it  was close to 150 degrees.

 Basically it seems the air temp sensor does not seem to drop low enough
fast enough meaning when I connect it 5 minutes of time passes and the
erratic miss begins and the RPM drops and at that point it reads 200 ohm
which tells me it's not leaning out near enough . Even when the reading was
107 ohm I plugged it in and got the same result. I also checked each of the
two sensor terminals to ground while running and never it shorted to

 I found a graph showing @ 140 degrees F it should drop to 80 ohm and in
the curve level out dropping no lower than 80 ohms even @ 212 degrees F.

 Now I didn't check the sensor in oil with thermometer yet I do know temps
aside it's resistance is still high when it's plugged in and the missing

 I still have more testing to do yet I did check all the wires in 2009 and
didn't find any issues to any of the FI components from the ECU plug
disconnected. I realize there is not much difference between 107 ohm and 80
ohm because there is a +/- 10 % my concern is maybe it's just not dropping
fast enough. All the D -jet used the same air temp sensor not talking oil
temp I do have the proper part in mine. This thing measures air temp and I
know the air temp through the oil bath into the IAD today was nowhere near
90 degrees. Yet the IAD does become quite warm just from engine heat  alone
and since the sensor is in the air flow yet threads into the IAD it seems
to me it must read some of this heat.

 I read the RE is plus 10% enrichment disconnected from a few  sources. I
cannot find what the actual temp/resistance relates to.

On Thu, Sep 12, 2019 at 5:24 AM Jim Adney <jadney at vwtype3.org> wrote:

> On 11 Sep 2019 at 21:10, William Jahn wrote:
> >  I do know the head temp sensor in the car now does not always read the
> > same resistance at the same temp and when I removed it I could see a
> > dark area under that whitish plastic cover and when I pulled the cover
> > back I could see an area just above the top of the sensor where the
> > insulation was one , no broken strands yet they were dull copper not
> > bright clean so perhaps that might cause an issue .
> The missing insulation won't cause a problem unless it allows the center
> conductor to short to ground on the steel crimp. That will bring you to a
> halt
> very quickly, but is seldom a problem except on the '68-9 cars where that
> sensor is cramped under the #4 exhaust port. On those engines the wire is
> forced to make a hard right angle turn just past the crimp, and they can
> short
> there.
> Surface corrosion on the copper strands won't add enough resistance to be
> measurable to your instruments, or to matter to our FI. If water has
> gotten
> down into the sensor element itself, that could cause an increase in
> resistance, or an intermittent problem, because the sensor element is just
> a
> tiny little puck with contact made by spring pressure on each end.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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