Porsche 912E 76 Operating and installation instructions

The Porsc he 912 E .. .
The techni ca l spec ifications are as follows:
Capacity: 1971 cm3
Stroke:
71 mm
Bore:
91 mm
Horse power:
developed at:
Torque:
develo
ped at:
86 hp/64
4900 rpm
98 Ibft/133
4000 rpm
.
.. is equipped with .. .
... a 2
Itr ., 4 cylinder engine (similar to that in the Type This motor has been fitted with
the electronically controlled AFC fuel injection thermal reactors and exhaust gas recirculation.

.
· . . a 5
speed transmission (based on transmission type 915) with modified transmission ratio
and a newly designed clutch operation mechanism.
·
.. a like the 911, a dual-circuit brake system,
disks brakes
without "inner ventilation" .
· bodywork similar to the 911 but with permanently
fixed rear side windows aswe
ll as other minor changes.
2

10
ENGINE
CRANK CASE, CYLINDERS, ENGINE MOUNTS
The crank case and the cylinders are the same as in the engine type 914/2 .0 Itr.
The following is new:
The engine mount.
It consists of a swung steel bar which is secured to the motor in the same way as in the 914.
The mounting points on the
chassis were moved outwards to the wheel wells however.
Warning:
installing the motor mount, note that the casted in part number (arrow) is pointing toward
t
he rear.
3

13 CRANK SHAFT DRIVE/PISTONS
All parts of the crank shaft drive are the same as in the basic motor. An additional fan-belt pulley
is fitted to drive the secondary air pump. It IS secured to the front of the air intake housing
by
means of a thr ee-armed block and is driven by means of a shaft from the center of
the cooling fan.
19 COOLI NG
The eng ine sh ee tmetal w as changed to conform to the 911 engine compartment configuration.
4

20 FUEL SUPPL V
The 912 E is fitted with an 80 Itr. (inc!. 8 Itr. reserve) fuel tank.
The fu
el pump is mounted on the front axle auxiliary mount.
The fuel
filter is the same as in the CIS injection It is secured to the l eft -h and wheel well in the
engine compartment
1
1. ) Fuel tank
2.) Fuel pump
3. ) Fuel filter
4.) Pressure regulator
5 .) Injection valv es
6.) Cold start valve
5

24 EL ECTRONIC F UEL INJECTION - AFC
The Porsc he 912 E is equipped with a motor that has aair flow controlled electronic fuel injection.
Before we describe this unit in detail, a few words about the accelerator cable.
The accel era tor cable is in two parts.The connector (arrow) is located within the engine compart-
ment behind the rear panel and is accessible when the cover to the guide channel is removed.
Construction and funct ion of the ATC injection
The component parts
1 Fuel Tank
2 Fuel Pump
3 Fuel Filter
4 Cold Start Valve
6 5 Fuel Injector
6
Pressure Regulator
7
Auxiliary Air Regulator
8
Throttle Switch
9
Air Filter
10 Temperature Sensor II
11 Battery
12 Ignition Switch
A Int ak e-air Sensor
B Throttle valve
C Air Sensor Flap
o Co ntrol Unit
Principles of Operation
The amount of fuel that is to be used is determined by the volume of intake air and the speed of the
motor.
The injector sequence is determi ne d by th e igni tion dis tr ibu tor breaker points.
The fuel required for cold starting is injected by the electro-magnetic cold start valve.
Warm-up en richment of t he fuel mixture is via the au xiliary air regulator in conjunction with the
temperature s ens or I in the intake-air Se n so r housing and t he temperature sensor II in the cylinder
head.
Fuel mixture enrichme nt for full load conditio ns is by me a ns of a throttle switch.
6
2

.
24 ELECTRONIC FUEL INJECTION - AFC
Description
Intake-Air Sensor
The intake-air sensor is located in the engine compartment at the right-hand side between the air filter
and the throttle housing (L) .
Construction
Aluminum housing (A)
with Bye-pass channel (5)
and
Adjustment screw (6)
Air sensor flap (1)
with Back pressure valve (8)
and Damping vane (2)
Damping chamber (7)
Return spring (9)
Potentiometer (B)
with Pump contacts (C)
Temp era ture sensor I (D)
Operation
The volume
of air that the motor can draw in is determined by the position of the thro ttle valve.
The resultant air
flow causes the sensor flap to deflect against the return spring. T he flap deflection is
transmitted via a shaft to the potentiometer which supplies a specific voltage to the con trol unit. The
temperature sensor I
is connected to the potentiometer and influences the control signal volta ge.
The injector which is activated by the control unit injects an exact amount of fuel appropriate to the
volume
of intake-air.
The damping vane
is designed to minimize sensor flap hunting. The function is as follows: with
deflection of the flap the damping vane is forced into the damping chamber. The resultant compressed
air
within the chamber can escape only through the release slit (S) . Sudden movements and hunting is
thereby reduced.
A fraction
of the air intake is detoured around the sensor flap via the bye-pass channel. The fuel-air
mixture for idle can be set by means of the adjusting screw (6).
A pump contact
is located within the potentiometer. When the sensor flap is deflected open the pump
contact
is closed and the fuel pump started.
Probl
em condition:
Motor does not start;starting dif ficulties; low efficiency.
Troubleshooting:
Remove the plug connected
to the potentiometer on the intake-air sensor. Connect an ohm meter
between the contacts 6 and
9. value: 200 to 400 Mea sure between contacts 7 an d 8.
Nominal value: 120
to 200 7
\
4

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--- . ---.------. "
-,
24 ELECTRONIC FUEL INJECTION - AFC
Throttle Switch
This switch provides the control unit with necessary
information for mixture enrichment and full load
cond itions.
It is not necessary to adjust this switch.
Problem
condition:
Low engine power
Troubleshooting:
Disconnect the wires
from the switch and connect an ohm meter between contacts 3 and 18.
Slowly open the throttle valve. The resistance must change from 00 to 0
Ignition Distributor
The ignition distributor provides the control unit with information concerni ng the speed of the
engine (rpm) and sequen
ce for activating the fuel injectors.
Operation
In addition
to de livering impulses to the ignition coil,
thecontact breaker points
also supply impul ses to
th econtrolunit. Each impulse (1) is converted to
a squ are wa ve (2) within the control unit . These
sq uare wave impulses are then presented to a gate (3)
whichprovides asingle
pu Ise output for each
sequ ence of four input pu Ises which are the resu It
of t wo re volutions of the motor crank shaft. That
is, f ollowi ng each revolu tion of thecrank shaft all
fo ur fuel injectors hav e received an ac tivat ing
impulse (5
). Thus the fuel injectors inject a de fin ite
amount
of fuel independent from the position of
th e air sensor flap. The injected fuel is always half
of the amount necessary for the correct fuel
mix ture. Si nce the crank shaft turns tw i ce for each
cycle, two injector sequences are put into operation
thus
each cylinder receives the full amount of fuel
for each firing stroke.
o
Zyl. 1
Zy
l.4
Zyl.3
Zyl.2
1 breaker
im pulses
- --t-
2 imp ul se
shaper
3 frequency
d
ivid er
4 air
flow senso r
fla p position
(pot
entiom eter)
'5 injection i mpul
(duration of
injection)
su ct ion
compressi
on
ign it ion
exhaust
o crankshaft angle
360 7 20 ·
I
:
control unit (e lectronic)
8

. .
24 ELECTRONIC FUEL INJECTION - AFC
TemperatureSensor I
The temperature sensor I is located in the intake air sensor housing and permanentely installed.
It can not be replaced separately. Its function is to measure the temperature of the intake air and
provide the
control unit with the appropriate information .
Troubleshooting:
Similar
to the intake-air sensor.
Temperature Sensor II
This sensor is located in the cylinder head. It provides the control unit with information concerning
engine temperature
and thus about the starting and warm-up enrichment.
Problem condition: the
motor does not start; warm starting difficulties; motor starts but stops again
almost at once; fuel consumption
too high; CO value is too high in slow running.
Troubleshooti
ng :
Connect
an ohm meter between temperature sensor II and ground.
Nominal value at
20°C/68°F motor and ambient temperature:
1.5
to 2 the motor temperature is above 80°CI176°F the value must be less than 300
9

24 ELECTRONIC FUEL INJECTION - AFC
Cont ro l Unit
The control u nit is located in the engine compartment within a cavity welded to the right-hand wheel
well.
The control
unit proc es s es information concerning
the
fo llowing:
Volume of intake air
Temperature
of i nt ake a ir
Motor rpm
Motor temperatu re
Intake air sensor deflec tion (full load)
It determi nes an d c ontro Is th einjection sequence and
duration.
The electronic con
tro l unit is composed of printed
circuits and
int egrated circu it components.
It is fitted wi th app rox imately 80 components.
The printed circu
it board is secured to the control
unit and presse d in to the socket until a spring snaps
into place.
Code explanation:
A Control un it
1 Control mul ti vibrator
1a Impul
se an d rpm divider
2
Multipl ier st age
2a Warm-up enrichment
3
Output st a ge
4 Fuel injector
5
Series resistor
I Control voltage from intake-air
se ns or
la Control impulse from distributor contact breaker point s
II Control signal
from throttle switch
Iia Control voltage
from starter swit ch/ temperature sensor II
10

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24 ELECTRONIC FUEL INJECTION - AFC
Fuel Injector
The volume of injected fuel is determined by the
length
of time the injector is open (i. e. the time of
the impulse from the control unit).
The injector is connected to +via the resistor (R).
(The control signal
from the control unit is of
negative potential.)
Injection Sequence
All injectors are activated simultaneously, once for
every crank shaft revolution.
Note:
The plug and socket assembly
is so arranged that it
can not be inadvertanly connected to an injector
of the MPC injection.
Pressure Regulator
The pressure regulator regulates the pressure of the
fuel in the ring supply line independent
of the
pressure in the vacuum line.
The spri
ng chamber of the pressu re regu lator is
connected to the intake air distributor via a hose .
Operation
By using this configuration the pressure
of the fuel
isadjusted independent
of the vacuum in the intake
air
distributor.
For example
High vacuum in the intake air
distributor (idle operation) - low fuel pressure. L ow vacuum in the
intake air
distributor (full load) -high fuel pressure.
This way, the difference between fuel pressure and intake air
distributor pressure always remains
the
same for all load conditions of the engine.
Troubleshooting:
Connect a
pr essur e gauge into the ring supply line. Disconnect the vacuum hose from th epressure
reg ulator. Start the motor .
Nominal value: 2.5 bar (36.75
psi approx.)
Reconnect the
hose the fuel pressure must now be lower.
11

24 ELECTRONIC FUEL INJECTION - AFC
Auxiliary Air Regulator
The engine requires during the warm-up phase a
richer
mixture . The increased volume is determined
by the control unit (signal from temperature sensor
II). The additional volume of air required for this
purpose
is regulated by the auxiliary air regulator
and detoured around the
throttle valve into the
intake air distributor.
Construction
The
auxiliary air regulator consists of a slide valve
and a bi-metal spring which
is enclosed by an
electrical heating coil.
Operation
If the engine is cold, the auxiliary air slide valve
is fully open. When the ignition switch is turned on
the heating coil starts
to warm up. With increase
in temperature the bi-metal spring becomes weaker
and the slide valve slowly shuts off the air intake.
Troubleshooting:
Electrical: Disconnect the plug
to the auxiliary
air regulator. Connect
an ohm meter.
Nominal value: approx. 30.
Mechanical: Remove
hose from the intake manifold
and
throttle housing. Blow air thru
from one side. If the motor is cold
the air must
flow freely. Switch on
the ignition, continue
to blow air thru
and observe that the air flow becomes
restricted
with increase in temperature.
.b
-
12

t
24 ELECTRONIC FUEL INJECTION - AFC
Troubleshooting:
Thermo switch: Engine temperature under 10°C/
50°F. Remove the plug from the
cold start valve and connect a
test lamp. Disconnect the wire
from contact 1 on the ignition
coil. Operate the starter motor :
the test lamp must initially be
bright and then visibly darker
within not less than 11 seconds.
Cold start valve: Connect a pressure gauge to the
ring supply line.
Operate the starter motor in
order to reduce the fuel pressure.
Remove the plug from the cold
start valve. Conne ct the cold
start valve by means of extra
wi res to ground and contact 15
on the ignition coil. Turn on the
ignition switch -- the fuel pressure
must fall.
Cold Starting Valve
The cold starting valve is located in intake air distributor and is activated by a thermo time
switch which is located adjacent to the intake air distributor.
Here are a few tips concernig trouble free operation of engines equipped with AFC injection .
All ai r lines and hos es and the intake -ai r sensor must be absolutely air tight . The sensor flap must be
able to move fr e ely over its entire range and not stick at any point.
All e le ctrical connections must be tight and free of corrosion.
Plug and socket color code: Fuel injector :
white
Cold start valve: blue
Thermo time switch:
brown
Intake-air sensor: black
When the vacuum line is disconnected, the fuel pr ess ure must be about 36 psi.
Ignition timing and vaive adjustment must be correct.
For idle and CO adjustment :
Idle is by adjusting the screw on t he throttl e housing.
Nom in al v al u e: 925 ± 50 rpm
The CO value is fa cto ry adjusted by me ans of the bye-p ass a dj ustme nt screw in the intake-air sensor
housing. The posi tion of this screw should be altered o nly when the no minalvalue of 0.5-1.2 % CO
ca n no t be obtained inspite perfect wo rkin g order of th e engine.
The CO-adjustment sc rew is covered by a plug. (Part No. 923.606 .991 .01)
Pl ug col or code:
Bl ack: Bo sc h setting
Blue: Pr oduction setting
Red: Service s etti ng 13

CIRCUIT DIAGRAM FOR THE AFC INJECTION
1 Multipo le plug
2 Ignition coil
3
Throttle switch
4 Intake-air Sensor
5 Temperature
sensor II
6 Cold start valve
7 Thermo
ti me switch
8 Fuel pump
9 Ground connection (Gnd)
10 Double relay
11 Auxiliary air regulator
12
Series resistor
13 Battery
14 Fuel injector cyl. 1
15 Fuel injector cyl. 2
16 Fuel
injectorcyl. 3
17 Fuel injector cyl. 4
Test Values
4. Intake-air Sensor : pin 6 + 9 = 200 -400
pin 7 + 8 = 120 -200
pin 36 +39 = 0
Air sensor flap = 00
pin 27 + 6 = 8 - 11 k at
100C (50°F)
2 - 3 k at 20°C (68°F)
- 2 k at 50°C (122° F)
3. Throttleswitch: pin 3+18, throttle open = 00 to 0
5. Temper at ure sensor II: at approx. 20°C (68° F) approx. 2.5
Pin 13 + 49 at approx. 80°C (176°F) below 300
6. Cold start valve : pin 45 + 46 = 4
7.Thermo time switch: below +30°C (86°
F)
above +40°C (104° F)
Pin G+ Gnd
25 -40
50 -80
Pin Wt Gnd
100 -160
Pin G+W 25 -40 50 -80
1 0. Double relay:
pin85+86b=
50 -100
12. Seriesresistor: pin 43 + Gnd. =
5-
14.- 17 .Fuel injector: pin 14 +41/32 +40/33/38115 +
37 = 2 - 3
14

26 EXHAUST SYSTEM
The 912 E engines are equipped with a secondary air injection, thermal reactors and EGR.
The
muffler and heat exchangers are also new.
The secondary air injection and the thermal reactors are designed
to reduce the CO and HC emission
in the exhaust. The purpose
of the EGR is to reduce the emission of nitric oxide (NOx ).
Secondary Air Injection
The air required for after burning the exhaust gases
is supplied to the exhaust manifold by means of a
motor driven air pump.
The air from the pump (1) is pumped via a back-up
valve (2) and a
distributor line (3) to the air
injection valve (4) which
is located immediately
behind the exhaust valve. The exhaust
gas after
burning takes place in the thermal reactor (5).
3
15

26 EXHAUST SYSTEM
Thermal Reactor
The thermal reactor mainly consists of two cylinders, one inside the other, (1) and (2). Cylinder 2,
which
is the combustion chamber, is provided with exactly defined holes (5). The outside wall is
covered with an insulating material.
-6-
-6-
4
1
-3-
Operation
The
hot exhaust gas which is mixed with the secondary air enters the reactor combustion chamber (3)
via the exhaust pipe (4). The
gas leaves the combustion chamber via the holes of the inner pipe (6)
and
is expelled from the reactor through the outlet port (7).
Due
to the arrangement of the holes in the combustion chamber the flow of gas is slowed down.
During this time the after burning process takes place.
16

in es
ne
26 EXHAUST SYSTEM
Exhaust Gas Recirculation (EGR)
Exhaust gas r ec irculation isdesigned to r ed ucethe
nitri c oxide emission (NOx)in aparticularload
range of the engine.
Construct ion:
The devi ce consists of a diaphragm contro l va lve (A),
exhaust gas (8) with filte r (C) and a v ac uum
contro l (D)
Operation
In thepart-load ran ge the cont rol va lvediaphragm is lift ed by the vacuum in the control line.
T he va lve opens and fresh a ir is mixed wi th a fraction of the exhaust ga s.
Th is contro ll ed "pollution" reduc es the nitric-oxide concentration (NOx)in the exhaust gas.
The funct ion of the EGR system must be tested every 30,000 miles. A cou nting mechanism is fitted
behind the speedometer which lights a warning lamp ma rk ed wh en the 30,000 mile limit has
been reached.
17

28 IGNITION SYSTEM
The 912 E motor is fitted with a battery ignition system.
Due
to the installation of the secondary air injection pump, the observation hole for the timing
marker is no longer accessible. The TDC marker (previously on the fan wheel) is now located on the
fan-belt
pully (arrow). An angle bracket which is secured to the air intake housing serves as reference
point .
Technical Specifications: Ignition System
Firing order:
1-4-3-2
Dwell angle:
Timing: 27° before TDC at 3500 rpm
vacuum
hose disconnected
Spark plugs: Bosch W 175 M 30 plug
gap 0.7 mm
Beru 175114/3 L
T
he distrib utor is fitted with avacuum operated advance and retard mechanism.The vacuum hose
fo r retarding is green.
18