[urq] Coolant temp sensor and duty cycle q's

[Louis-Alain Richard]

Nathan,

I ordered myself a new sensor (035 919 501, OEM 47$, round connector) no
later than this morning because I found that the one bought last summer
(049 919 501, jobber, 8$, flat connector) when I did the head job is not
the correct unit. 

Both are white but 049 is rated at 0-125C and the good one (035) is
rated at 0-150C. What I found (with the 049) is the ECU _thinks_ the
engine is hotter than reality and reduce the frequency valve duty cycle
too soon. So my engine RPM is always a little low when warming up. And,
most important, the fuel mileage is 3 liter/100 km (4 mpg) worst than
usual! 

BTW, be very careful when tightening the sensor in the head: that's the
reason why I had to replace it last summer...  The thing is really
fragile (10mm brass threads on an hollow tube!! ) and using a 17 mm or
19 mm socket with a 1/2 inch ratchet makes a good grip, enough to shear
it off very easily... Don't ask how I know.

Live and learn,

Louis-Alain


-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On
Behalf Of n-engelbert at terrans.net
Sent: Monday, December 01, 2003 10:00 AM
To: urq at audifans.com
Subject: [urq] Coolant temp sensor and duty cycle q's

I went to pick up the ECU coolant temp sensor that I had ordered 035 919
501, and it's very visibly different than the one that is currently in
the
car.  The replacement has sort of a button connector on top whereas the
one
currently in the car has a spade terminal.  Both have white tops.  I
haven't removed the one in the head, so I don't know the thread
size/pitch
on it, but it looks like it will take at least a 17 mm socket, maybe 19,
to
remove.  The new sensor is much smaller, maybe 13 mm socket, with a
m10x1
threaded portion.

The current sensor is most definitely dead.  The resistance to ground,
with
the ecu lead disconnected, is open circuit.

Now for some duty cycle readings:  Taken with engine warm, O2 connected,
temp sensor connected (although open circuit).  At warm idle, duty cycle
either 20 or 80%.  Idle switch closed, full throttle switch closed, 21
or
79%.  Idle switch disconnected, full throttle closed, 21 or 79%.  Values
are with duty cycle meter connected both ways to the connector by the
ignition coil.

These all look to be that of a cold engine upon cranking, or are
adjusted
WAY off.  O2 sensor voltage through all of this is about 0.74V, pretty
steady.

This is most probably the reason that my car stumbles while warming up,
the
only question now is why the duty cycle doesn't change?

Can I assume that a new temp sensor will change this?  If so, is the one
with the round connector on top the one I want, or is there a part with
a
spade connector that I just can't find in the family album under any
car?

Thanks!

Nathan Engelbert
83 UrQ 900453