http://www.fordscorpio.co.uk/24vlooms.htm
2.9 24V Cosworth Engine and Auto Gearbox Control Looms
The 24V Cosworth engine uses the same Powertrain Control Module (PCM (EEC-V)) as the 16V engines but there are important differences from the DOHC designs. The engine loom passes over the top of the gearbox and disappears from view in between the cylinder heads inside the V. Here it has proved to be vulnerable to leaking engine coolant - two owners have reported ruined looms and electrical faults caused by coolant, so loss of coolant should be vigourously and persistently investigated and repaired as soon as possible.
The 24V Loom was armoured with a tough outer sheathing on production vehicles after 1/4/95 so it appears that Ford realised that the looms were subject to chafing and gave them additional protection. My own 24V Estate was built in October 1995 and has behaved impeccably since I bought her in July 1998.
Note: Remember that in several locations the Scorpio uses very thin wires which carry multiplex signals at 5V rather than more traditional 12V analogue signals used in almost all other vehicles. This makes the wiring looms and connectors much more susceptible to damage and is considered one of the weaknesses of the cars now they are in the secondhand market.
Circuit Description
The electronic engine control system uses a network of sensors, switches,
and solenoids and the powertrain control module (PCM) (A147) to control fuel
flow, exhaust gas recirculation (EGR), ignition system functions, engine
idle speed, fuel evaporation to the atmosphere, transmission control and
feedback functions for emission-related components.
Voltage Supply
With the ignition off, voltage is present at pin 55 of the PCM (A147) to
protect the data stored in memory. With the ignition in run, the ignition
coil (T1) and the fuel pump relay (K4) receive voltage. All other components
of the engine control system receive voltage from the fuel pump relay (K4).
Pins 40, 71 and 97 of the PCM (A147) also obtain voltage from the fuel pump
relay (K4).
Ignition
The ignition system is controlled by the electronic Distributorless Ignition
System (DIS) module (A23). The DIS module (A23) controls the ignition coil
(T1) and the crankshaft position sensor (B43) and is connected to pins 23,
48, 49, and 50 of the PCM (A147). The signal from pin 50 is used to detect
intermittent ignition system faults. Pin 49 receives a Profile Ignition
Pickup (PIP) value which is used by the PCM (A147) to determine the
crankshaft position. The PCM (A147) also uses the PIP-signal to control gear
shifting times (engine speed).
Fuel Pump
The fuel pump relay (K4) receives voltage from the ignition switch (N278)
and is controlled by pin 80 (pin 54 with passive anti-theft system (PATS))
of the PCM (A147). Pin 40 of the PCM (A147) is used as a fuel pump monitor
input. Current flows to the inertia switch (N61) which shuts off the fuel
pump in the fuel tank unit (A31) in case of an accident. The fuel pump runs
constantly during normal operation, and the system pressure is preserved
when the engine is shut off.
Transmission Control
The transmission hardware unit (A40) consists of the Transmission Speed
Sensor (TSS), the Transmission Oil Temperature (TOT) sensor and five
solenoids. The PCM (A147) provides outputs to the transmission through pins
1, 53, 54 (pins 72 and 80 with passive anti-theft system (PATS)) to control
the shifting operations of the transmission.
The stop lamp switch (N15) sends a "brake applied" signal to pin 92 of the
PCM (A147). This data is used to adjust the engine operations during
deceleration.
Pins 10, 79 and 80 of the PCM (A147) lead to the instrument interface module
(A35).
Power Steering Pressure Switch
The power steering pressure switch (N96) sends a signal to pin 31 of the PCM
(A147) when the pressure is high. Under high power steering pressure, the
PCM (A147) increases the idle speed.
Engine Cooling Fan
The engine cooling fan relay (K45) and the engine cooling fan motors (M37,
M38) are controlled by pins 17 and 68 of the PCM (A147).
Instrument Cluster
The instrument cluster (A30) with integrated trip computer obtains a "fuel
flow" value from pin 43 of the PCM (A147) in order to calculate fuel economy
and distance-to-empty displays for the driver.
A/C Compressor Control
The A/C Wide Open Throttle (WOT) relay (K32) can be energised when pin 69 of
the PCM (A147) is connected to ground. This will cause the A/C compressor to
be disengaged, thus reducing engine load.
Voltage is applied to pin 41 of the PCM (A147) when the dual pressure switch
(N76) is closed. This information is used to determine engine load and to
control engine idle speed.
Octane Adjust
Pin 30 of the PCM (A147) measures the voltage drop across the octane adjust
plug (D2) and uses this information to modify ignition spark advance.
Diagnostic and Ground Connections
Pins 13, 15 and 16 of the PCM (A147) lead to the Data Link Connector (DLC)
(D20).
Pins 24, 51, 77 and 103 of the PCM (A147) are connected to ground G10.
Pin 25 of the PCM (A147) is connected to ground G7.
Solenoids
The fuel injectors (Y108, Y109, Y110, Y111, Y112, Y113) obtain their voltage
from the fuel pump relay (K4). The PCM (A147) (pins 75, 101, 74, 100, 73 and
99 or pins 70, 96, 20, 95, 93 and 94 with passive anti-theft system (PATS))
controls the six fuel injectors continuously and individually. The injection
quantity, that is, the duration of the input signal, is determined by the
temperature, load and rpm of the engine as well as by the composition of the
exhaust gases. The longer the pulse, the greater the amount of fuel that
passes through the injector.
The idle speed control valve (Y13) obtains its distribution voltage from the
fuel pump relay (K4). The PCM (A147) compares the stored desired engine idle
speed value with the actual engine idle speed and regulates the idle speed
control valve (Y13) from pin 83. The idle speed control valve (Y13) varies
the air volume into the engine via an auxiliary air passage.
The canister purge solenoid valve (Y1) is needed to open and close the
activated carbon canister. When the valve is energised by connecting pin 56
of the PCM (A147) to ground, the fuel vapours from the fuel tank can be
drawn into the engine, mixed with the intake air and burned.
The Electr. Vacuum Regulator (EVR) solenoid valve (Y33) allows a measured
quantity of exhaust gas to be directed back into the intake manifold. The
exhaust gas introduced into the intake manifold dilutes the incoming mixture
and reduces peak gas temperatures, thus reducing NOx emissions. The valve is
controlled by pin 47 of the PCM (A147). The EGR system does not operate
during conditions of over-run or wide open throttle.
The intake air control valve (Y67) receives voltage from the fuel pump relay
(K4) and is controlled by pin 44 of the PCM (A147).
Sensors
Pin 91 of the PCM (A147) serves as ground for the Exhaust Pressure
Transducer (EPT) sensor (B40), the Throttle Position Sensor (TPS) (B8), the
heated oxygen sensors (HO2S) (B47, B48, B87 and B88), the Engine Coolant
Temperature (ECT) sensor (B10), the Air Charge Temperature (ACT) sensor
(B5), the transmission range sensor (B120), the oil temperature sensor of
the transmission hardware unit (A40), the power steering pressure switch
(N96) and the octane adjust plug (D2).
The Exhaust Pressure Transducer (EPT) sensor (B40) and the Throttle Position
Sensor (TPS) (B8) receive a reference voltage of 5 V from pin 90 of the PCM
(A147).
The Exhaust Pressure Transducer (EPT) sensor (B40) measures the pressure
difference in the feed exhaust and sends its signal to pin 65 of the PCM
(A147). The sensor is part of the EGR system.
The Throttle Position Sensor (TPS) (B8) consists of a potentiometer mounted
on the throttle blade shaft that sends its signal to pin 89 of the PCM
(A147). Using this signal, the module can compute the position of the
throttle valve (idle, partial load, or wide open) and use the input to help
calculate fuel delivery.
The pre-catalyst heated oxygen sensors (HO2S) (B47, B48) measure the amount
of oxygen in the exhaust gases. Bounce signals are sent from the
pre-catalyst heated oxygen sensor RH (HO2S) (B48) to pin 60 and from the
pre-catalyst heated oxygen sensor LH (HO2S) (B47) to pin 87 of the PCM
(A147). This measurement is made so that the PCM (A147) can maintain the
air/fuel mixture composition close to the value of Lambda=1 for correct
operation of the catalytic converter. Since the sensors do not function
until they have reached their operating temperature, they contain heating
elements to speed warm-up time.
The post-catalyst heated oxygen sensors (HO2S) (B87, B88) are installed
behind the catalytic converter and send bounce signals to pin 35 and 61
respectively of the PCM (A147) to ensure correct operation of the
pre-catalyst heated oxygen sensors (HO2S) (B47, B48).
The Engine Coolant Temperature (ECT) sensor (B10) (a temperature-dependent
resistor) receives its input voltage from pin 38 of the PCM (A147). The
sensor provides the PCM (A147) with the engine operating temperature needed
to help calculate fuel delivery.
The Air Charge Temperature (ACT) sensor (B5) provides the PCM (A147), pin
39, with a signal proportional to the temperature of the incoming air
charge. The data is used to help calculate fuel delivery.
The transmission range sensor (B120) sends a start input signal to pin 64 of
the PCM (A147). The PCM (A147) will not allow the engine to start unless the
transmission is in park (P) position.
The Transmission Oil Temperature (TOT) sensor of the transmission hardware
unit (A40) sends its signal to pin 37 of the PCM (A147).
The Vehicle Speed Sensor (VSS) (B11) sends a square wave signal, whose
frequency is proportional to the vehicle road speed, to pin 58 of the PCM
(A147).
The Mass Air Flow (MAF) sensor (B22) measures the quantity of air passing
into the engine via the air filter. The information is then fed back to the
PCM (A147), pins 36 and 88, and is used to help calculate fuel delivery.
The crankshaft position sensor (B43) provides the electronic DIS module
(A23) pins 5 and 6, with the position of the crankshaft. This data is used
for correct timing of the injectors at engine start-up.
The Transmission Speed Sensor (TSS) of the transmission hardware unit (A40)
provides the PCM (A147), pin 84, with the transmission shaft speed. The data
is used to control the shifting sequence for the transmission.
The camshaft position sensor (B41) provides the PCM (A147), pin 76, with a
reference point for the number 1 cylinder, which is necessary to ensure the
correct sequence of injector opening.
Connections
The tables below do not attempt to describe the entire loom or every connection. They are designed for the purpose of testing with a multimeter between the PCM multiplug C402, the bulkhead connectors C113 and C110, and at the terminal point on the relevant multplug. If you know which pin is involved in each multiplug you can test a single connection from the PCM to the gearbox for both continuity, resistance and insulation.
The 24V Loom refers to a C113 connector on the engine bulkhead for the gearbox control loom instead of the C112 but the two are identical. Remaining connectors are shown in this figure:
A view of the engine bulkhead will be of use, too:
Gearbox (THU) Loom Connections
| PCM C402 | Engine Bulkhead C113 |
Colour, Usage |
THU C604 |
| 27 | 31 | BK/YE Shift Solenoid 1 | 16 |
| 1 | 32 | BK/BU Shift Solenoid 2 | 14 |
| 53 | 38 | BK/OG Shift Solenoid 3 | 7 |
| 72 | 28 | BK/WH Shift Solenoid 4 | 9 |
| 37 | WH/RD to 25 | BK/RD Trans Oil Temp Sensor (TOT) | 4 |
| 80 [54] | 33 | BK/WH Modulated Lock-Up Solenoid | 5 |
| 81 | 30 | BK/RD Electric Pressure Control Solenoid (EPC) | 12 |
| 84 | 36 | WH/VT Transmission speed sensor (TSS) | 2 |
| 64 | 27 | WH/BK Transmission Range Sensor (TR - PRNGL) | - |
| 61 | 15 | WH/GN Post Catalyst LH HO2S Sensor | C867 Pin 1 |
| 101 [96] | 14 | GY/OG Post Catalyst LH HO2S Sensor | C867 Pin 3 |
| 35 | 19 | WH/BU Post Catalyst RH HO2S Sensor | C855 Pin 1 |
| 100 [95] | 20 | GY/VT Post Catalyst RH HO2S Sensor | C855 Pin 3 |
[Without PATS]
Engine Loom Connections
| PCM C402 | Engine Bulkhead C110 |
Colour, Usage |
Sensor Location |
| 83 | 5 | BK/YE Idle Speed Control Valve (IAC) | Inlet Manifold C720 Pin 2 |
| 70 [75] | 37 | BK/WH Injector 1 (INJ1) | Inlet Manifold C718 Pin 1 |
| 96 [101] | 4 | BK/YE Injector 2 (INJ2) | Inlet Manifold C874 Pin 1 |
| 20 [74] | 36 | BK/BU Injector 3 (INJ3) | Inlet Manifold C876 Pin 1 |
| 95 [100] | 30 | BK/OG Injector 4 (INJ4) | Inlet Manifold C875 Pin 1 |
| 93 [73] | 12 | BK/GN Injector 4 (INJ5) | Inlet Manifold C716 Pin 1 |
| 94 [99] | 3 | BK/RD Injector 4 (INJ6) | Inlet Manifold C875 Pin 1 |
| 38 | 33 | WH Engine Coolant Sensor (ECT) | Front C Head C859 Pin 2 |
| 39 | 14 | WH/VT Air Charge Temp (ACT) Sensor | Inlet manifold C719 Pin 1 |
| 89 | 8 | WH Throttle Position Sensor (TPS) | Throttle Body C869 Pin 2 |
| 90 | Thru shorting connector | YE Throttle position Sensor (TPS) | Throttle Body C869 Pin 1 |
| NONE | 27 | BN/RD Power for above ECT ACT & TPS | |
| 85 | 26 | WH/VT Camshaft Position Sensor (CMP) | Cam Cover C872 Pin 1 |
| 76 | 31 | BN/WH Camshaft Position Sensor (CMP) | Cam Cover C872 Pin 2 |
Note, numbers in square brackets indicate connections for vehicles not equipped with PATS.
In addition, some modules or sensors essential for engine management are not connected directly to the PCM. The Electronic Distribution & Ignition System is one: terminal numbers on the EDIS module are given in column 1. In the 24V the ignition coil is built into the EDIS.
| EDIS Module # | Engine Bulkhead C110 |
Colour, Usage |
Sensor Location |
| EDIS 5 | 20 | BN/RD + Crankshaft Position Sensor (CKP) | C858 Pin 2 |
| EDIS 6 | 15 | WH/RD - Crankshaft Position Sensor (CKP) | C858 Pin 1 |
| EDIS10 | 10 | WH/BU EDIS | C712 Pin Not Shown |
| EDIS12 | 16 | WH/GN EDIS | C712 Pin Not Shown |
| EDIS 11 | 22 | BN/YE EDIS | C712 Pin Not Shown |
Several other elements are not actually part of the loom. These can be checked by reference to the C402 connector on the PCM and the appropriate wire on the instrument - Terminal nos on each multiplug given in the 3rd Column.:
| PCM C402 |
Colour, Usage |
Terminal No | Sensor Location |
| 56 | BK/OG EVAP canister purge valve | 2 | LH B/Head C764 |
| 36 | BN/BU MAF Sensor | 2 | Inlet Piping C784 |
| 88 | WH/BU MAF Sensor | 1 | Inlet Piping C784 |
| - | BK MAF sensor - check earth | 3 | Inlet Piping C784 |
| 47 | BK/GN - Electric Vacuum Regulator (EVR) | 1 | LH Bulkhead C765 |
| 48 | WH/GN EDIS Module | 2 | C766 |
| 23 | WH/RD EDIS Module | 4 | C766 |
| 49 | WH/BK EDIS Module | 1 | C766 |
| 50 | WH/VT EDIS Module | 3 | C766 |
|
65 |
WH/BU Exhaust Pressure Transducer (EPT) | N/K | C918 |
| 31 | WH Power Steering pressure switch (PSP) | 1 | C820 |
| 87 | WH/RD Pre Cat LH HO2S sensor | 1 | Exhaust C931 |
| 99 [94] | GY/RD Pre Cat LH HO2S sensor | 3 | Exhaust C931 |
| 60 | WH Pre Cat RH HO2S sensor | 1 | Exhaust C1010 |
| 73 [93] | GY Pre Cat RH HO2S sensor | 3 | Exhaust C1010 |
| 44 | WH Intake Air Control Valve (VIS) | 2 | C768 |
| 58 | WH/BU Vehicle Speed Sensor (VSS) | 2 | C854 on THU |
Take your time to work through these tables so that you understand them before you attempt to go fishing with the multimeter. When checking for insulation, bear in mind that some wires are interconnected and provide power to several items at once. It is for this reason I have concentrated on the Pin numbers on the PCM and their corresponding termini.
Do not attempt checks on part of a loom without ensuring that the other end is disconnected, or you will in effect be measuring the equipment it is connected to.
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Copyright © 2002