[urq] hesitation, bucking on takeoff - not resolved yet!

[Buchholz, Steven]

To respond to the earlier thoughts on what signals are important once
the engine is running ... the WX engine must have all engine timing
signals operating properly for the engine to run ... I have not
personally confirmed the report about disconnecting the Hall sender ...
but I agree that it may well be true ... but implying that the ECU
ignores the input when the engine is running does tend to create an
incorrect impression of how the ECU operates and how important the
proper function of the Hall sender is.  

I can tell you for a fact that the electronics for the MAC-02 F/TCU
*always* intends to use the signal from the Hall sender on the dizzy as
a control input to the timing generation circuitry in the ECU.  The
program running in the computer may be able to keep up with things once
the engine is running with the Hall sender unplugged ... but I can
guarantee you that if you grounded that Hall sender signal the engine
will stop immediately.  Here again, I have not demonstrated this
experimentally, this is just based on what I know of the circuitry from
the reverse engineering I've done.  

Why is this important?  If you look at the shutter in the distributor,
the window where the Hall sender allows the flywheel signal to pass
through is relatively small.  If the Hall Sender malfunctions in a way
where it grounds the signal during this window, the F/TCU will not send
ignition pulses to the coil driver for two revolutions of the engine.  I
guess the message I'm trying to get across is ... don't discount the
distributor Hall sender signal too lightly.  

Others have suggested other things like chewed flywheel teeth ... I'm a
bit skeptical that this is the problem because the "speed" signal
actually gets smaller as the engine spins faster, so the fact that this
is a problem at lower RPMs makes me think that it is not a problem with
the teeth.  

As I posted yesterday, I also agree with Dave's assertion that it may
well be an issue with the sensors on the flywheel ... 

Steve B
San Jose, CA (USA)
> 
> >Do these even come into play once the engine is started?  I thought
> >once the engine "synced up" Hall,TDC and Ref sensors, that the only
one
> >that is really used from that point on is the Hall sensor.
> 
> Once the engine is started, the hall sensor may be disconnected. But
the
> ECU needs the ref mark sensor and the timing(speed) sensor in order to
> determine
> engine position. It reads the ref mark sensor (60 deg BTDC) and then
> counts
> flywheel teeth to determine engine position for timing. I would
perform
> the
> checks on pages 32-34 of the IST manual and verify functionality of
the
> speed and ref sensors.