90tq problems continue

[ed armstrong]

--- Huw Powell <human747 at attbi.com> wrote:
>
> > Well I'm trying to make some progress with the
> 90tq
> > but seem to have taken a few steps back.
> >
> > Yesterday I moved the O2 sensor to the exhaust
> > manifold and the car seemed to run better (i.e.,
> less
> > smoke) but I think I just got lucky. Read on.
> >
> > After this  I went to test the current readings at
> the
> > CIS differential pressure regulator with a little
> test
> > jig I bought many years ago. I was surprised went
> the
> > current meter read 0 ma. Unpluged the O2 sensor,
> no
> > change in current.
>
> OK, so it is not reading the OXS. A steady 0 mA is
> the "limp home" mode.
>
> Check your OXS wiring for shorts, check the OXS
> output voltage, and as
> you say later, if you can, swap in another computer.
>
> > Removed the air boot and lifted the
> > meter plate (car not running of course) to
> simulate
> > cold enrichment. Nothing, still reading 0 ma !
> (should
> > have gone briefly rich at this point).
>
> The only way the air plate could affect the current
> is if the
> potentiometer is used for that by the ECU.  I
> suspect you would also
> have to have a couple of other things correct for it
> to react - idle
> switch open, WOT switch closed.  And I don't think
> it does this, anyway.
>
> > I did verify
> > that there is voltage at many CIS sensors when the
> > ignition is on, but curiously the diff press
> sensor
> > only read 5V when the other were 11.5-12V.
>
> If by diff. press sensor you mean the potentiometer
> on the side of the
> airbox, that is correct.  it gets 5v and ground at
> pin 1 and 3 and the
> output is pin 2, varies with airplate position.
>
> >
> > Then I pulled the engines codes as some
> recommended;
> > got 4444 (no faults) but then 1111 which is
> defective
> > memory in computer ! I'm really bummed at this
> point,
> > because its lookin like I fried my CIS computer
> > somehow. I infer this from the code and the fact I
> get
> > no current at the diff press regulator. Could I be
> > wrong ?
>
> What is the DPR current at a cold start?  If the ECU
> is working, you'll
> see something around 30-60 mA for a moment, slowly
> dropping to 0 mA over
> a minute or two.  This is the open loop warm up
> enrichment in action.
>
> How is your temp sender (should be one of those
> awful MFS units for
> CISE3)?
>

Huw,

The DPR current is 0 ma all the time, regardless of
cold or warm start. That and the code 4444 is why I
think the CIS fuel computer is shot.

Havent given to much thought to the pontentiomter yet
but I'll eventually check it too. The 5 V I refer to
is for the DPR signal, definitely not the
potentiometer.

The air plate test I described comes straight out of
the Probst book. You have to hold the throttle open
for this. On cold start you should see a quick
increase in DPR current signaling momentary enrichment
(I guess this assumes the potentiometer is working
correctly too).

I replaced the small coolant sensor with a new one a
while ago. I believe this what the computer uses. The
larger one directly beneath it (both are on the water
inlet to head) is what is used for the instrument
cluster readings according the Bentley.

=====
-ed

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