CIS theory?

[Konstatntin Bogach]

I checked these two sensors and replaced them cause both were dead. It
made difference even though I did not understand exactly how they are
used by ECU. Thanks for explanation about air temp sensor. 
Now I am trying to understand how to test deceleration cut-off valve and
I am getting mad gradually cause I can't understand how the valve itself
works looking at Bentley manual and Scott's Mockry site (graphical pin
out diagram). I mean, what is driving mechanism of the valve? What
exactly and how opens it? I see contradictions in Bentley:
- it shows some switch control unit in place of radiator fan stage 1
relay (layout schema)
- it depicts the valve as solenoid but testing procedure and electrical
schema confuse me.

What is that electrical connection to the valve? Is it used for sending
signal from valve to ECU or from ECU to valve? 
I did not look under the hood (I am still on crutches and it makes me
laisy) but looking in the Bentley I don't see from where vacuum line is
coming to the valve. I assume it comes from intake manifold directly
(not through any valves).

Thank you for your help.

Konstantin Bogach
5ktq 89

Ameer Antar wrote:
> 
> I'm not sure which temp sensor yer referring to, but I'll assume it's that
> tiny single-wire sensor on the head. This sensor is critical for the ECU,
> as the others have other functions. You have a 5kT right? It's on the head
> on the side near the radiator. It looks very unique b/c of only wire coming
> out of it. I believe there's a picture of it on 25.28. The ECU uses it for
> a variety of things, like going from open-loop to closed and I believe
> affects timing.
> 
> The air temp sensor in the intake manifold is used for setting up advance
> of the ignition timing. Very hot air will cause the ECU to retard timing
> which is critical in a turbo engine. When air is compressed in a turbo or
> supercharger it gains heat. This is a law of physics. [A/C's work on the
> opposite fact, decompressing air cools it.] It's important to know the
> intake temp in a turbo b/c the intercooler might have a problem or the car
> might be idling in traffic, so the air is not being cooled after being
> compressed. Hot air is very bad for combustion as it raises combustion
> temps and can cause detonation. So this is a refinement of ECU control. The
> problem is once you test the sensor, I think it has to be replaced, b/c you
> need to pull back the insulation, which leaves it vulnerable to dirt,
> corrosion, and breakage. But I believe Scott M. has a few good tips about
> testing both the air and ecu temp sensor. Check out the page at
> http://www.sjmautotechnik.com/
> 
> look under troubleshooting section. good luck.
> 
> -ameer
> 
> At 10:27 AM 11/2/00, you wrote:
> >Thanks again.
> >I know functions of all those switches. But what I don't know it is how
> >and when ECU uses signal form the first one you mentioned and from air
> >temp sensor.
> >
> >Konstantin Bogach.
> >
> >Ameer Antar wrote:
> > >
> > > the temp sensor is the one that activates it. as soon as I start driving in
> > > the morning, the AFR gauge moves around, so the sensor does put out a
> > > signal, it's just not reliable until it's up to full temp, I think maybe 2
> > > mins. The designers I believe chose a relatively low coolant temp to switch
> > > to closed loop, so it doesn't take very long, and in a turbo engine, it's
> > > not much of a problem.
> > >
> > > There are at least 4 temp sensors in the engine. They all can go bad. The
> > > very small one in the head which is about .25" round and has single wire
> > > coming from it, is used by the ecu. I think there is also a
> > > thermotime-switch for the ISV system and one for the cold-start injector.
> > > The big 4-pin sensor under the upper coolant hose has multiple functions,
> > > mostly I think for the a/c and check system. I'm really not sure about all
> > > their functions, but all you need to do is test each w/ an ohmeter
> > > according to the Bentley or even the Haynes has good info for ignition/ecu.
> > > sensors are a good place to start in diagnosing trouble. good luck.
> > >
> > > -ameer