[T3] Bad day at the (FI) office
Jim Adney
jadney at VWType3.org
Fri Mar 25 08:16:08 PDT 2016
On 25 Mar 2016 at 8:22, Daniel Nohejl wrote:
> In general, is 64 ohms too low for the CHTS when fully warm?
Yes, the CHTS should be 2000 - 3000 Ohms at room temp and will come
down below 1000 when warm, but I don't think I'd expect it to ever
get below 100 Ohms. I'm not certain about that, but to come down
another order of magnitude in resistance, I'd expect it to have to go
up an order of magnitude in temp. That put's it WAY out of the
reasonable range. You're unplugging it when you measure it, right?
Otherwise, you're actually measuring the parallel combination of the
sensor and the brain circuitry. I don't know how you could get 64
Ohms. I didn't think Bosch made anything that had that range. Maybe
yours is partly shorted, or .... Isn't that a part that you've
swapped? Hard to imagine that you could have 2 with the same
behavior.
Somewhere, I have a graph that I made of the temp curves for each. It
turned out that the curves were straight lines if you plotted then on
log-antilog paper (IIRC.) I can't find that graph right now, but I'll
keep looking. If I can find it, I should be able to give you some
idea of what temp 64 Ohms might indicate.
Just for shits and grins, I grabbed a CHTS that measured ~2400 Ohms
at room temp and stuck it in ~185 F water. The resistance dropped to
just under 400 Ohms. So this resistance falls faster than I expected,
but I still think 65 Ohms is too low. What does it measure when cold?
> Is 64 ohms too low for the air temp sensor when fully warm?
No, that sounds about right. For a given temp, that one measures
about 1/10 as much resistance. And, on your car, that sensor actually
senses the oil temp. It sits in a place where it gets splashed by the
cam gears.
> I´m not using a K-jet manual....I was talking about the manual that
> Russ Wolfe often posted pages of on The Samba and on his website. Tram
> uses it as well and refers to it as a workshop manual they used at the
> dealership. All the section headings I´ve seen begin with "K" so I
> just called it the K manual. Like these for example (they?should link
> to Photobucket?:
Ahhh, Okay. THAT K manual. K stands for Kraft: German for Power. It's
the portion of the dealer service manual set that deals with carbs
and FI.
> I think that in my frustration I might not have been clear. The meter
> isn´t giving conflicting info. It´s telling me I´m rich with the
> resistor installed at the CHTS and this is in accord with my poor fuel
> consumption. 99.9% of my driving the last month has been in this
> state: resistor installed, bad MPG, rich AFR readings.
All done with the pressure sensor tweaked, right? What happens if you
put the pressure sensor back to where it started and leave the 100
Ohm resistor in?
--
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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