[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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