help - Motronic M1.5 adaptation issues

[Aribert_Neumann at magna.on.ca]

Greetings all.
Background:   I have adapted a Bosch Motronic M1.5 fuel injection system
(complete system - intake manifold, air filter housing with integral MAF, all
sensors, vehicle wiring harness, 3 wire O2 sensor, ignition coil and ECU)  from
a '92 GM of Europe 2.0 L engine (Opel/Vauxhall) and adapted to a formerly
carb'ed '92 Isuzu 2.3 L engine.  The Motronic system manages ignition timing via
the ECU - the GM distributor consists of a large boss cast on the end of the cam
cover with the distributor shaft an extension of the cam with only a rotor under
the cap.

 I made a 3/4 in. thick aluminum adapter plate to mate the GM intake to the
Isuzu head.  I removed the crank trigger wheel and sensor from the GM engine
(internally crank mounted wheel) and attached externally to the front of the
Isuzu crank pulley.  THe only other loose sensor from the Bosch system (balance
of sensors integrated in the intake assy.) is the water temp unit which I tapped
into the water manifold behind the thermostat - same as on the GM engine.  I
removed the ignition reluctor/hall effect sensor from the Isuzu dist. and am
(trying) to use the dist. strictly to distribute the high voltage generated at
the coil. The centrifugal advance in the Isuzu dist. has not been removed at
this time.

Results:  Engine runs reluctantly, very low idle - under 500 rpm and is
unresponsive to the throttle.  I have adjusted the Isuzu dist. housing for
maximum advance where the starter motor will still crank the engine.  Resultant
ignition timing is approx. 20 deg.  AFTER  TDC.  Headers started glowing a very
faint, dull red within a minute, my max run time.  I disabled the high tension
lead from the Bosch coil and attached my ignition bypass unit (little black box,
sold by JC Whitney 15+ years ago, generates a spark stream to bypass points or
electronic ignition).  Engine runs good (at no load - vehicle is not driveable
at this time), responsive to throttle changes, had an 800 rpm idle with
occasional drop to 600 rpm with a correction to 1200 rpm and idle resettled at
800 rpm until the engine was up to temp.  Once the engine was up to temp the
idle was very steady.   Ran engine in this mode at idle for about an hour.  Due
to the spark stream generated by the ignition bypass unit I was not able to use
my inductive timing light to check the timing.

Questions:  1.  Why would the ECU retard the timing?  And why would the engine
act as if the timing was too far advanced when cranking the engine when I tried
to compensate by advancing the dist. and still using the timing signal from the
ECU?  I was expecting the resultant timing to be too far advanced due to the
cumulative effect of the centrifugal action still present in the Isuzu dist. and
the ECU timing.
2.  Initially I thought that I had mispositioned the crank sensor relative to
the trigger wheel.  If I had the crank sensor mispositioned by 20 deg retarded
the injector firing should be retarded also.  Would the engine not reflect this
when running?  Does anyone know the static angular relationship between TDC,
crank sensor location and the missing teeth on the trigger wheel for Motronic
systems?  I am making an assumption that the relationship would be similar for
various versions of the Motronic series.
3.  What can I do to correct item 1?  While I have a good selection of
mechanical and fabrication tools, I am very limited in electrical/electronic
diagnostic tools.
4.  As part of the sorting out process, I assume the EPROM might need to be
reprogrammed to reflect the differences between the 2.0 and 2.3 L engines.  This
is not something that I would attempt do to my lack of programming knowledge.
If I outsourced this, what can go wrong in doing so?  What is a worst case
scenario?  I do not have a spare back-up ECU and would have to have one shipped
out of Europe.  In the future, I intend to get duplicates of all unique sensors
and a spare ECU.
5. If I am unable to correct the ECU controlled ignition timing problem, I
intend to use a Crane XR-700 (formerly Allison) ignition module as a stand alone
device for ignition, in lieu of the ECU ignition control, and not disable the
centrifugal advance in the Isuzu dist.  The Isuzu dist. also had (currently
plugged off) a vac. advance.   Can this be hooked up to intake manifold vacuum
or does it need the vacuum signal from the former carb?  Would there be any
benefit of using the vac timing advance with the fuel injection?
6.  I anticipate a potential lean condition at higher revs - current injectors /
injection pulse time sized for a 2.0 L instead of the 2.3 L.  I intend to
purchase a $30  "A/F monitor" and do plug cuts early on in the shake down
period.   Would I be able to use the signal from the O2 sensor for both the ECU
and the A/F gage or will the gage degrade the signal?  Welding a second O2
sensor boss on the headers will void the lifetime warranty and I expect to run
this vehicle for about 8 years.


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