CIS Fuel Injection
By C.A.Stoddard
This new system introduced on the 1973 2.4 911-T is now standard on
all U.S. 2.7 911 Porsches. It has proven to be exceptionally reliable,
troublefree, and has good fuel economy and driveability (ref. July ‘73
Pano). Once in a while, starting difficulties have been experienced, all
of which are readily explained and cured. They are summarized in the
following 4 points:
(1) Flooding
This rarely occurs, but can happen as the starting
(7th) injector works whenever the engine is cranked by the starter
motor with the accelerator 1/4 or more open. The best cure is to crank
the engine with the throttle slightly open (less than 1/4) to draw air
only through the cylinders; then wait a minute and hold throttle wide
open while starting—and remove your foot promptly when it fires!
(2) Air Leak
Because the system senses air flow and then meters
the appropriate amount of fuel, any air leak between the sensing
device and the cylinders will result in an excessively lean possibly
non-combustible mixture. Once in a while a CIS engine will cough back
through the induction system, and blow the large rubber air duct off
its connection to either the throttle valve or the sensor plate, thus
giving a substantial air leak. This is usually easily recognized when
the engine starts and runs (on the 7th injector) for about 2 seconds,
and then dies for lack of fuel. The cure is to loosen the retaining
clamp, and carefully reseat the profiled rubber duct—a 5 minute task
requiring a screwdriver.
(3) Vapor Lock
In very hot weather, after an engine has been
running and then shut off, it may be reluctant to restart. This is
caused by gasoline vaporizing in the injector nozzles and lines due to
heat absorbed from the cylinder heads. The cure is to wait a few
minutes and try again, or after removing the plastic air filter
housing and cartridge, lift the air sensor plate about 1/2" while
the key is on for about 4 seconds. This allows the system to pump cool
fuel into the injectors. Then start the engine and replace the filter.
(4) Starting (7th) Injector
If the 7th injector does not work while cranking
the engine, the engine will not start. To check its operation, remove
the primary distributor wire (to prevent spark and/or fire) and the
rubber air duct mentioned in (2) above. While a second person holds
the accelerator down and cranks the engine with the ignition key,
observe (hopefully) a generous spray of fuel below the throttle plate.
If there is no fuel spray, check the electrical feed (via starter
solenoid) or replace the injector. If stranded in the boonies, a fast
push start or manual activation of the throttle sensor plate will
suffice.
All of the above have been rare in occurrence. On
‘74 models, the injectors were moved up into the intake manifolds, a
cooler environment.
The technically oriented PCA’er is cautioned
about making experimental and/or exploratory adjustments to the idle
air flow and mixture. These are the only two adjustments on the
system, they only affect the idle range of the engine, and are very
sensitive. If the engine does not run well, and the CIS is suspect, it
may be checked with a special test pressure gage and valve assembly
which will readily diagnose and pinpoint trouble.
12/73 |
