temp sensor & poorly running 90q

[Bernard Littau]

I cannot recollect which sensor it was as far as upper or lower, but I 
am sure it was a two connection sensor.  I am guessing it was the lower 
one on the 4kq, as the upper one appears to be the thermo-time switch 
from looking at the Bentley.  In any case, you are a bit handicapped 
using this advice as the 90q is likely different.

In the "it's good to have several pairs of eyes on the problem" nature 
of this list,  Jan Pinkowish aptly points out:

Point of reference here:
--the cold resistance of this sensor is 3-5kohm when cold, i.e., 20degC
--resistance when at operating temp is usually 300-500 ohm.

Failing sensor at high resistance causes rich running.
Failing sensor at low resistance causes rough running until the engine gets 
to operating temp.

See Bentley 25.76

The 4kq Bentley talks about a VW 1490 adapter in section 25.95 test
2b.  It mentions using the 15K ohm side, which is where I got my 15K as
cold starting point.

My resistance numbers were empirical, as in where the car seemed to run best.  I am not at all surprised that my numbers would be higher resistance values than spec, cars always seem to run a better just a bit rich.  Be warned that while the car might run "better" just a little rich, it will kill your catalytic converter if you do this for a long time.

In the end, it boils down to that the ECU gets engine temperature information from some sensor.  If this sensor is inaccurate, it could cause the symptoms you are seeing just by being too rich in fuel.  I had everything from stumble, no power, gas smell, sooty exhaust, to in-the-exhaust detonation of mixture.  

Best,

Bernard


DePenning, Charles [EPM/MTN] wrote:

>Ok, so this brings up a question- which sensor is it?  IIRC, there are two
>in relatively close proximity to each other on the top water neck connection
>to the head- one on top which has two wires connected to it and looks pretty
>simple (and makes the dash temp gauge go to zero when I unplug it) and the
>Multi-Function Sensor on the bottom of the water neck, which has I think
>three connections.  I seem to remember a bit of confusion about these two
>sensors and their respective functions in the past- something like on the
>4kq's they work one way, and on the 90q work another.  I believe Huw had
>some insight on this.  
>Bernard, which sensor connection did you pull off and use the resistors on?
>
>Thanks for the input, guys.   
>
>
>Charley 
>-----Original Message-----
>From: William Magliocco [mailto:magliocc at rocketmail.com] 
>Sent: Tuesday, March 30, 2004 12:37 PM
>To: Charles.DePenning at EmersonProcess.com
>Cc: bernardl at acumenassociates.com; quattro at audifans.com
>Subject: temp sensor
>
>Sounds really familiar-I had an '88 VW fox that would start fine COLD then
>puke on its own gas when it warmed up.  !@#$^&*( stalled out on me on an
>interstate about 10 miles from home.
>
>Temp sensor was open or had insanely high resistance. 
>Bernard's idea is very creative w(ith the series resistors), but I simply
>went to the "furrin kar parts" place and bought a new one.
>
>We electrical types call that an "NTC"
>thermistor-negative temperature
>coefficient...resistance goes DOWN as temperature of the device INCREASES.
>
>HTH
>Bill in Atlanta
>
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