Slipstream - January 2010

Cliff’s Ramblings
by Cliff Blackshear
Every now and then something shows up in the
shop and we need Porsche to help us in getting
to a correct resolution. There are times that
only they can find an answer. It does not happen often, but
it can happen. I was involved in one case that could only
be solved by them in a reasonably timely manner.
It was a check engine light issue on a 04 Boxster.
Owner says that check engine light is intermittently
flashing while driving. It doesn’t do it every day but it
happens pretty often.
So we check the DME (fuel/ignition microprocessor)
for fault codes. No faults recorded. I drove the car and after
awhile I experienced it. Duplicated the symptom. Brought
the car into the shop. Kept it running to preserve everything
possible in system software and interrogated with system
tester. No faults...
This is not supposed to ever happen per EPA
mandated OBD2 requirements. OBD system is there to
help keep cars running clean. Combustion process has to
be very complete under all circumstances. The monitoring
software is designed to be very sensitive to any minor
abnormality. A flashing light is supposed to be the highest
priority warning. It means that a problem has occurred that
can damage catalytic converters and totally compromise
not only emission output, but also the performance level
should be greatly reduced. With a flashing light there is a
high probability that one or more cylinders are misfiring.
This 04 Boxster ran like a scalded cat. It never
exhibited any uneven running problems for me. I get John
Gladwill involved and discuss this with him. His ability to
think out of the box is unrivaled in my world and I look
to his thoughts often. We help each other out all the time
and it’s kinda fun. He drives the car a few times and looks
at data as I had and also came up blank. He did however,
establish a way to drive the car and reproduce the event
more consistently. Which happened to be “Drive it like ya
stole it.” There is a surprise (If ya know John yer chuckling
about now.)
In our shop we take a lot of pride in getting things
done without any help. It is important to us that we get it
done correctly and then report to Porsche what we found.
We are one of 20 monitoring dealers and reports flow from
us all the time.
Yet this car had us stumped. So I file request for
technical assistance. The reply was “That cannot happen.
The design of the software will not let that happen,
ever! Are you positive it is the check engine light that
is flashing?”
That’s Not Possible!
After a few phone conversations we are told someone
is coming out to see this and lend a hand.
The gentleman that came out (and I will not name
factory people here ever) was amazing. He told me about
writing the software for the 02 vario-cam plus application.
The system that not only varies cam timing, but also valve
lift. Indicated that the variable valve lift was the hardest
thing he ever dealt with. Trying to get smooth engine
operation when a system goes for 4mm to 9mm valve lift
was quit an undertaking... now I ramble.
So anyway, he brings his own laptop to plug into the
car and John takes him for a drive. He finds the root of the
check engine light in minutes.
In Germany in 04 (I dunno about now,) they had
an emission inspection process that was way different
from ours.
In the trunk of a Boxster is a relay board on the left
side behind the trim panel. Not all of the relay positions
are occupied by relays. Some are open positions. When a
vehicle is due for an emission/safety inspection across the
pond, the technician accesses that board. They apply a 2
pronged jumper wire in one of the open relay positions.
This puts the system into diagnosis mode to ensure all
systems are on line and functioning in the fuel ignition
world. When the pins are jumped, the check engine
light flashes to indicate the DME is running a self
diagnostic routine.
So guess what? Inside the wire harness that exited that
board and went straight to the DME, was an intermittent
short between these two circuits. We did not find any place
on the harness that showed any signs of pinching, incorrect
routing, nothing. When nothing was found with the harness
the DME became suspect. So we eliminated these two
circuits to the DME and test drove. Over and over and over
and over. Problem was eliminated. We monitored every
input to the DME while driving and found everything to
be absolutely spot on. Car was declared right and has not
had a single problem since........
I cannot say definitively that only a factory engineer
could have found that, but the information about those
circuits and their purpose has never surfaced on this side
of the Atlantic. In our wiring diagrams at that time, the
wires and their connections were innocuous to us. They
had no meaning and no explanation. I have not looked
lately to see if maybe the connections have at least been
given a name. Like ROW emissions or something.
Love what I do!
Cliff
January 17