IAC wiring
12-11-2008, 08:48 AM
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IAC wiring All I can find is colors for the IAC, Lt Green/Blk.=Coil B low, Lt.Blue/Blk=Coil A low, Lt. Blue/white=Coil A High, Lt. Green/white=coil B high. So what does that mean?
Is the high positive and the low ground? Or is the body of the IAC ground, and the high and low are positive, that move the pintle in and out?
My IAC shows zero on the datalog, so I am trying to diagnose the problem. I had recently painted the IAC, so maybe it is not grounding?
Is the high positive and the low ground? Or is the body of the IAC ground, and the high and low are positive, that move the pintle in and out?
My IAC shows zero on the datalog, so I am trying to diagnose the problem. I had recently painted the IAC, so maybe it is not grounding?
12-11-2008, 09:44 AM
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IAC is a stepper motor, there are two drive phases
and the phase relation determines direction while a
steady voltage (current) will lock the rotor in place.
The pintle is a worm screw that the rotor (nut) will
move as it turns. The pintle can become disengaged
(seen one just fall out, while chasing IAC performance
problems). Painted and modified for connector angle,
not clear whether that had anything to do with it.
Coil A and coil B should have continuity across and
isolation between. Neither involves the case / ground.
In normal operation all 4 wires ought to have some
voltage on them relative to ground. Some PCMs
have the IAC driver components deleted (most
drive-by-wire ones, sparse exceptions) and the
Coil_-_ outputs will show only noise, tens of
millivolts on all four.
IAC=0 on the datalog means it's been put closed
all the way and still is not happy with idle RPM.
Do you see a large negative LTIT+STIT in the
logs? Actual airflow > desired airflow?
With positive pressure before the throttle blade,
the IAC steps vs airflow table is probably nohow
close to realistic. And any blade hole might want
smaller.
and the phase relation determines direction while a
steady voltage (current) will lock the rotor in place.
The pintle is a worm screw that the rotor (nut) will
move as it turns. The pintle can become disengaged
(seen one just fall out, while chasing IAC performance
problems). Painted and modified for connector angle,
not clear whether that had anything to do with it.
Coil A and coil B should have continuity across and
isolation between. Neither involves the case / ground.
In normal operation all 4 wires ought to have some
voltage on them relative to ground. Some PCMs
have the IAC driver components deleted (most
drive-by-wire ones, sparse exceptions) and the
Coil_-_ outputs will show only noise, tens of
millivolts on all four.
IAC=0 on the datalog means it's been put closed
all the way and still is not happy with idle RPM.
Do you see a large negative LTIT+STIT in the
logs? Actual airflow > desired airflow?
With positive pressure before the throttle blade,
the IAC steps vs airflow table is probably nohow
close to realistic. And any blade hole might want
smaller.
12-11-2008, 10:07 AM
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It is a Big Stuff 3 system. Pretty basic tables. In the logs and in real time, it shows desired IAC, which moves around in relation to TPS,RPM etc.. but the actual IAC reads 0 at all times.
12-11-2008, 02:39 PM
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IAC motor gives no feedback so there is no basis
for an "actual", only "intended". PCM has to keep
track of steps made, away from initial position.
And assume the motor follows.
So maybe you are just looking at a dummy #, one
that maybe some other mfr's hardware might make
valid but GM's doesn't (?).
Might try commanding IAC to a series of positions
and verify whether engine RPM responds. That will
at least give you the sense of whether IAC is on
the job, and doing this w/ stock PCM and HPTuners
does make RPM change happen for me so ought to
be doable w/ the BS3 if its "control console"
provides a direct IAC position command ability.
for an "actual", only "intended". PCM has to keep
track of steps made, away from initial position.
And assume the motor follows.
So maybe you are just looking at a dummy #, one
that maybe some other mfr's hardware might make
valid but GM's doesn't (?).
Might try commanding IAC to a series of positions
and verify whether engine RPM responds. That will
at least give you the sense of whether IAC is on
the job, and doing this w/ stock PCM and HPTuners
does make RPM change happen for me so ought to
be doable w/ the BS3 if its "control console"
provides a direct IAC position command ability.
