I found this part of the NTSB final report extremely interesting.
The OBD II like data from the fuel injection computer was very
useful. This is an open loop system so no telling exactly
what was going on with the engine. PL

Excerpt from http://www.ntsb.gov/aviation/SEA/lnarr_98A083.htm

TESTS AND RESEARCH

The two Motec electronic ignition engine control units (ECU's)
were removed from the aircraft and the data stored within them
was retrieved using a computer driven data recovery program
provided by the United States distributor of the ECU's (J.G.M.,
Inc., of Huntington Beach, California). The data recorded by the
ECU's had been gathered approximately once each second from
engine start to the instant of impact (see ECU Data Chart), and
included the following parameters:

a. Elapsed time. [Time] (in minutes and seconds).

b. Engine speed. [RPM] (in revolutions per minute). 

c. Throttle position. [TP %] (in percent of full throttle).

d. Manifold pressure. [MAP kPa] (in kilopascals).

e. Engine coolant temperature. [ET C](in degrees Celsius).

f. Ambient air temperature. [AT C] (in degrees Celsius).

g. Main battery voltage. [BAT V] (in DC volts).

h. Oil temperature. [AUX T] (in degrees Celsius).

i. Engine load fuel metering. [EP %] (in percent of full).

j. Fuel injector pulse duration. [APW %] (in milliseconds).

k. Fuel injector duty. [DTY (in percent of capability).

Each of the data entry points from the time of power application
at takeoff to the moment of data collection termination was
reviewed by the investigative team, and selected data from the
last five minutes of the flight was graphed on an elapsed time
chart using Microsoft Exel (see Thunder Mustang Last Five
Minutes graph). In addition, selected data from the last 117
seconds of the flight was graphed in an elapsed time sequence
which allowed finer scrutiny of the relationship between data
points (see Thunder Mustang Last Two Minutes graph).

According to the ECU's for both left and right bank cylinders,
the throttle was moved from a taxi-level setting (around 20%),
to the full forward (100%) position approximately 20.7 minutes
prior to the time at which data collection terminated. As the
throttle was moved to that position, where it remained for about
34 seconds, the engine speed increased from around 1,800 rpm to
about 5,100 to 5,200 rpm.

As both the throttle position and the engine rpm increased, the
engine load (EP), injector pulse duration (APW), and injector
duty (DTY) all followed the throttle/RPM increase in a fairly
linear manner. According to both ECU's, the EP increased from
around 20% to about 98 to 100%, the APW increased from about 3
milliseconds (mS) to about 7 to 8 mS, and the injector duty
increased from around 10% to 60 to 70%. About one minute and
twenty seconds after the full power application for takeoff, the
left ECU indicated that the throttle was reduced to about 63%
and the engine rpm dropped to around 4,250.

The right ECU indicated approximately the same RPM, APW, and
DTY, but its throttle position reading and EP reading, which
takes into account throttle position, read approximately nine
percent higher than that of the left ECU. This difference,
according to both the engine and airframe manufacturers, is
caused by a base-line measuring error which resulted in the
throttle position reading on the right ECU being approximately
nine percent greater than its actual position. This difference
was constant throughout the flight, except when the throttle was
in the full-power position, where the RPM and EP readings are
limited by the reading limit of 100%.

The throttle position remained around 63% for about two minutes,
and then there was a two and one-half minute period where the
throttle was moved to various settings between 20% and 80%
(although during most of this time the throttle settings were in
the 40's). At the end of this period, the throttle was advanced
to and remained in a range of 62% to 67%. It was operated in
this range for the next twelve and one-half minutes, and then
was reduced to the 0% (idle) position over a period of about
eight seconds. The throttle remained at idle for the next minute
and forty-five seconds, and over a period of about 35 seconds,
the RPM gradually dropped to about 2,200 RPM. With the throttle
still at idle, the RPM jumped back up to about 3,100 RPM for
about five seconds, and then gradually dropped over a 20 second
period to about 2,100 RPM.

Then once again, the RPM rapidly increased, this time to a high
of 3,900 RPM. Almost immediately the RPM once again began to
drop, and about 23 seconds later had returned to the 2,100 RPM
range. Then about five seconds before the end of data
collection, the throttle was pushed forward to about 72% and the
engine RPM climbed to just below 4,100 RPM. This throttle
movement took place over a period of about four seconds. During
the four second throttle push-up, the RPM, EP, APW, and DTY all
followed in a linear manner as they had during the initial
push-up at the beginning of the flight.

Then about one second before the end of data collection, the
throttle was retarded. The last throttle position recorded by
the left bank ECU was 62%, and the last recorded by the right
bank was 13% (idle). As the throttle was reduced during the last
second of data collection, all four of the aforementioned
parameters dropped in value. It was also noted that during the
minute and forty-five seconds the throttle was at idle, the
manifold pressure (MAP) slowly climbed, with minor fluctuations,
from around 82 or 83 kilopascals (kPa) to around 89 or 90 kPa.

According to the aircraft manufacturer, because of the location
of the pressure sensor in the induction plenum, this increase of
pressure is a direct reading of the change in the ambient
pressure as the aircraft descended.


A review of the data also revealed that just over one minute
after the throttle was advanced for takeoff, the battery voltage
dropped below 12 volts, the level at which the alternator
warning light comes on, and remained there (between 10.8 and
11.9 volts) for the remainder of the flight (except for one
spike to 12.2 volts as the throttle was moved forward about four
seconds before data termination). Additional data was collected
by an auxiliary data terminal on the right ECU that had been set
up to collect engine oil temperature information. It showed that
throughout most of the flight, the oil temperature ranged
between 110 and 114 degrees Celsius (230-240 Fahrenheit). Data
also indicated that although the oil temperature had dropped to
a range of 20 to 30 degrees Celsius (68-85 degrees Fahrenheit)
during the minute and forty-five seconds the engine was at idle,
at the termination of data collection, the temperature was
recorded at 92.5 degrees Celsius (198.5 degrees Fahrenheit).

During the investigation, the Vision Micro Systems VM 1000
engine monitoring system was recovered from the wreckage and
taken to Vision Micro Systems Inc., of Bellingham, Washington,
for retrieval of the stored data. The RAM data taken from this
unit represents only the information being processed at the
moment power to the system was terminated. The recovered data
indicated that 28 minutes and 15 seconds had elapsed from the
time of engine start to the moment when power to the unit was
terminated (see Vision Microsystems Data chart). The unit also
indicated that the elapsed time from the application of takeoff
power to the last moment of data collection was between .30 and
.39 of an hour (18 to 23 minutes). The data further showed that
although the maximum recorded battery voltage during the flight
was 13.22 volts and the minimum was 10.84 volts, at the time
of data termination the voltage was about 11 volts (10.96).


Also, according to this system, although the last alternator
output recorded was zero amps, at some time during the flight,
the output had reached as high as 44.63 amps. The final data
also revealed that the oil pressure was 55 pounds per square
inch, the oil temperature was 200 degrees Fahrenheit, and the
fuel flow was 30.5 gallons per hour. The final data also showed
that the exhaust gas temperatures from nine of the twelve
cylinders were between 430 and 630 degrees Fahrenheit during the
last reading. According to the technician at Vision Micro
Systems, the higher temperature readings from the exhaust of the
other three cylinders (746, 835, and 1,198 degrees), were the
result of the shorter elapsed time (in milliseconds) since the
last time these cylinders had generated an exhaust pulse.


ADDITIONAL DATA AND INFORMATION

During the investigation it was determined that twice before,
after the illumination of the alternator light, the aircraft had
flown using battery power only. During one of the flights, the
aircraft ran on battery power for about 45 minutes while en
route to Nampa, Idaho, from California. During the other flight,
which was a return flight from Florida to Nampa, the aircraft
flew on battery power for approximately three hours. According
to the airframe manufacturer, the reason for both alternator
failures was a wire that had broken due to vibration. Since that
time, an expansion loop had been added to the wire to reduce the
chance of future failure due to vibration. According to the
engine manufacturer, the coil pack can produce a spark as long
as the battery provides at least seven volts, and the ECU's can
monitor/control engine performance down to a low of six battery
volts. It was also noted that in addition to the 12 volt main
battery, the aircraft also carries a 12 volt backup battery
(although of lesser ampere-hour output).

During the investigation, it was also noted that, according to
the airframe manufacturer, when the aircraft's throttle is
reduced to idle in flight, the combination of short, direct
exhaust stacks (no muffling system) and an intentionally
enriched fuel mixture, produces a considerable amount of loud
"backfiring."

On July 6, 1998, the aircraft wreckage was released to Dan
Denny, CEO of Papa 51 Ltd., at Nampa Idaho.
 
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