1991 FORD FESTIVA sensor

PINPOINT TEST TP - THROTTLE POSITION SENSOR

Fig. 11: Identifying TP Circuits

TP CIRCUIT PIN IDENTIFICATION
1.6L
1. Turn ignition off. Install BOB. Turn ignition on. Measure voltage between BOB test pins TP and SIGRTN while opening throttle.
Compare voltage to specification in TP SENSOR OUTPUT VOLTAGE
table. Go to next step if output voltage is not within
specification.
TP SENSOR OUTPUT VOLTAGE
2. Turn ignition off. Unplug TP sensor connector at throttle body. Using jumper wires, connect VREF and SIGRTN wires on harness
Temperature °F (°C)Ohms
-4 (-23)15,000
32 (0)5210
68 (20)2500
104 (40)1100
140 (60)600
176 (80)300
NOTE:Enter this test only when a Code 12 is displayed during QUICK T EST S procedure or when directed here
from another PINPOINT TEST.
CircuitECA PinBOB PinWire Color
1.6L
IDL1E28GRN/ORG
SIGRTN2C46, 49BLK/YEL
TP2G47ORG
VREF2A26WHT/BLK
Throttle Opening(1) Voltage
1/81.00
1/41.60
3/82.37
1/22.74
5/83.15
3/43.43
7/83.60
(1)Voltage may vary by 15 percent.
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connector to corresponding terminals on TP sensor connector. Turn ignition on. Measure voltage between TP and SIGRTN terminals on
TP sensor while opening throttle. Compare voltage to specification in TP SENSOR OUTPUT VOLTAGE
table. If voltage is within
specification, repair TP wire to ECA. Go to next step if voltage is not within specification.
3. Turn ignition off. Unplug TP harness connector. Turn ignition on. Measure voltage between VREF and SIGRTN wires on TP harness
connect-or. If voltage is 4-5 volts, replace TP sensor. If voltage is not 4.5-5.5 volts, go to next step.
4. Measure voltage between VREF wire on TP harness connector and ground. If voltage is 4-5 volts, adjust or replace throttle position
sensor. If voltage is not 4-5 volts, go to PINPOINT TEST VREF
.
PINPOINT TEST BP - BAROMETRIC PRESSURE SENSOR

Fig. 12: Identifying BP Sensor Circuits

1.3L
BP sensor is incorporated into ECA; it cannot be checked or serviced separately. If Code 14 is set and cannot be cleared, replace ECA.
1.6L
Turn ignition off. Connect BOB. Remove dust cover from BP sensor, located on passenger side cowl. Turn ignition on. Connect vacuum pump
to BP sensor. Measure voltage between pins BP and SIGRTN on BOB while applying vacuum to BP sensor. See BAROMETRIC
PRESSURE SENSOR OUTPUT VOLTAGE table. Replace BP sensor if voltage is not as specified.
BAROMETRIC PRESSURE SENSOR OUTPUT VOLTAGE
PINPOINT TEST EGO - EXHAUST GAS OXYGEN SENSOR
EGO CIRCUIT PIN IDENTIFICATION
1. Warm engine to operating temperature, and let idle. Unplug EGO sensor. Measure voltage between EGO sensor connector (sensor side) NOTE:Enter this procedure only when a Code 14 is displayed during QUICK T EST S procedure or when
directed here from another PINPOINT T EST . T o prevent unnecessary replacem ent of com ponents, note
following non-EEC item s m ay be at fault: unusually high or low atm ospheric pressure, blocked vacuum
lines, or basic m echanical engine com ponents.
Vacuum (In. Hg.)(1) Voltage
03.84
53.36
102.66
151.93
201.26
25.58
(1)Voltage may vary by 15 percent.
NOTE:Enter this test only when a Code 15 (lean) or Code 17 (rich) is displayed during QUICK TESTS
procedure.
CircuitECA PinBOB PinWire Color
EGO
1.3L2N29BLU
1.6L2D29BLK
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and ground. With engine at idle, voltage should fluctuate between 0.2-0.8 volt.
2. Increase and decrease engine speed while reading voltmeter. When engine speed is decreasing, voltage should decrease. When engin e
speed is increasing, voltage should increase. If voltage is within specification, go to next step. If voltage is not within specification,
replace EGO sensor.
3. With ignition off, install BOB. Leave ECA disconnected. Unplug EGO sensor connector. Measure continuity between EGO test pin and
EGO sensor connector wire. If continuity exists, EGO circuit is okay; return to QUICK TESTS if sent here from there. If not sent here
from QUICK TESTS, replace ECA. If voltage is not as specified, repair VMREF wire to VAF. If continuity does not exist, service EGO
sensor wire to ECA.
PINPOINT TEST PRC - FUEL PRESSURE REGULATOR CONTROL SOLENOID

Fig. 13: Identifying PRC Circuit & Connector

PRC CIRCUIT PIN IDENTIFICATION
1. Locate Fuel Pressure Control (PRC) solenoid on cowl panel, next to canister purge solenoid. Unplug PRC solenoid connector. Remo ve
both vacuum lines. Plug vacuum port from engine vacuum source. Apply vacuum to remaining port. Replace PRC solenoid if it does not
hold vacuum.
2. Turn ignition off. Connect BOB. Leave ECA disconnected. Reconnect wiring to PRC solenoid. Turn ignition on. Apply vacuum to PRC
solenoid. Connect jumper wire between PRC test pin on BOB and ground. If vacuum drops to zero, PRC solenoid function is okay.
Return to QUICK TESTS if sent here from there. If vacuum does not drop to zero, go to next step.
3. Turn ignition off. Unplug PRC solenoid connector. Turn ignition on. Measure voltage between VPWR wire on harness connector and
gr o u n d . If vo l t a ge is n o t h igh e r t h a n 1 0 vo l t s, r e p a ir VP WR wir e t o ma in r e l a y. If vo l t a ge is h igh e r t h a n 1 0 vo l t s, go t o n e xt step.
4. Turn ignition off. Unplug PRC solenoid connector. Turn ignition on. Measure voltage between solenoid connector VPWR wire and
solenoid connector SIG wire. Connect jumper wire between PRC test pin on BOB and ground. If voltage is higher than 10 volts only
when solenoid is activated, replace solenoid. If voltage is not higher than 10 volts only when solenoid is activated, go to next step.
5. Turn ignition off. Connect BOB. Leave ECA disconnected. Unplug solenoid connector. Measure resistance between SIG test pin and
solenoid connector SIG wire. If resistance is not less than 5 ohms, repair SIG wire to ECA. If resistance is less than 5 ohms, go t o n e xt
step.
6. Turn ignition off. Connect BOB. Leave ECA disconnected. Unplug solenoid connector. Measure resistance between SIG test pin and all
other test pins. If resistance between SIG PRC test pin and any other pin is less than 5 ohms, repair PRC wire to ECA. If resistance
between PRC test pin and any other pin is greater than 10,000 ohms, replace ECA.
PINPOINT TEST CANP - CANISTER PURGE CONTROL SOLENOID
NOTE:Enter this test only when a Code 25 is displayed during QUICK T EST S procedure or when directed here
from another PINPOINT TEST.
CircuitECA PinBOB PinWire Color
PRC (1.6L)2K31BRN
NOTE:Enter this test only when a Code 26 is displayed during QUICK T EST S procedure or when directed here
from another PINPOINT TEST.
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Fig. 18: Identifying VREF Circuit & Connector

VREF CIRCUIT PIN IDENTIFICATION
1. On 1.3L, go to next step. On 1.6L, turn ignition on. Measure voltage between throttle position switch VREF and SIGRTN wires. See
VREF CIRCUIT PIN IDENTIFICATION
table. If voltage is 10-12 volts, repair short to voltage. If voltage is zero volts, go to next
step.
2. Turn ignition on. On 1.3L, measure voltage between Black and White-Black wires at VAF sensor. On 1.6L, measure voltage between
White-Black and Blue/Yellow wires at BP sensor. If voltage is 4-5 volts, VREF circuit is okay. If voltage is zero volts, go to next step. If
vo l t a ge is 1 0 - 1 2 vo l t s, r e p a ir sh o r t t o vo l t a ge .
3. Turn ignition off. Install BOB. Install 4EAT tester (if vehicle is equipped with 4EAT transaxle). Unplug connector from VAF, TP, and
BP sensors as applicable to vehicle. Measure resistance between VREF terminals on ECA and 4EAT module. Also measure resistance
between ECA VREF terminal and TP, BP, and VAF VREF harness connector terminals. If any measurement is greater than 5 ohms,
repair wire in question. If resistance is less than 5 ohms for all measurements, go to next step.
4. Turn ignition off. Disconnect 4EAT module (if equipped). Unplug connector from VAF, TP, and BP sensors as applicable to vehicle.
Measure resistance between ECA VREF pin on BOB and ground. If resistance is not greater than 10,000 ohms, repair short in VREF
circuit. If resistance is greater than 10,000 ohms, go to next step.
5. Turn ignition off. Disconnect ECA. Unplug connector from VAF, TP, and BP sensors as applicable to vehicle. Measure resistance
between ECA SIGRTN, 4EAT, and all SIGRTN pins on BOB. If any measurement is greater than 5 ohms, repair wire in question. If
resistance is less than 5 ohms for all measurements, go to next step.
6. Turn ignition off. Install BOB. Connect ECA. Connect 4EAT module (if equipped). Turn ignition on. Measure voltage at ECA SIGRTN
test pin on BOB. If voltage is 0-1 volt, go to PINPOINT TEST PGC
. If voltage is not 0-1 volt, repair short to voltage on SIGRTN
circuit.
SUMMARY
CircuitECA PinBOB PinWire Color
1.3L
SIGRTN2D46, 49BLK
VREF2K26WHT/BLK
1.6L
SIGRTN2C46BLU/YEL
VREF2A26WHT/BLK
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Back To Article
H - T EST S W/O CODES
1991-92 ENGINE PERFORMANCE Ford Motor Co. T rouble Shooting - No Codes
INTRODUCTION
Before diagnosing symptoms or intermittent faults, perform steps in BASIC TESTING and TESTS W/CODES articles in the ENGINE
PERFORMANCE Section. Use this article to diagnose driveability problems existing when a hard fault code is not present or vehicle is not
equipped with a self-diagnostic system.
Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific
component, system test or adjustment.
Use intermittent test procedures to locate driveability problems which DO NOT occur when the vehicle is being tested. These test procedures
should also be used if a soft (intermittent) trouble code was present but no problem was found during self-diagnostic testing.
SYMPTOMS
SYMPTOM DIAGNOSIS
Symptom checks cannot be used properly unless problem occurs while vehicle is being tested. To reduce diagnostic time, ensure steps in
BASIC TESTING and TESTS W/CODES articles in the ENGINE PERFORMANCE Section were performed before diagnosing a symptom.
These symptoms are available for diagnosis.
Backfire through induction or exhaust.
Dieseling (run-on).
Lack of power.
Spark knock (pinging).
Stalls/quits.
Stumble/hesitation during acceleration.
Misses/surges.
Idle is fast/slow return to idle.
Id l e is ro u gh .
Engine speeds up.
Cranks normally/no start.
Cranks normally/slow to start.
Poor fuel economy.
Exhaust smoke/odor.
Fuel odor/leaks.
Fails emission test.
BACKFIRE THROUGH INDUCTION OR EXHAUST
Check vane airflow meter.
Check idle speed control solenoid.
DIESELING (RUN-ON)
Check idle speed control solenoid.
LACK OF POWER
Check vane airflow meter.
Check throttle position switch.
Check heated exhaust gas oxygen sensor.
Check A/C switch.
Check wide open throttle A/C (WAC) relay.
SPARK KNOCK (PINGING)
Verify ignition timing is correct.
Check vane airflow meter.
STALLS/QUITS NOTE:Som e driveability problem s m ay have been corrected by m anufacturer with a revised com puter
calibration chip or com puter control unit. Check with m anufacturer for latest chip or com puter
application.
NOTE:For specific testing procedures, see SYST EM/COMPONENT T EST S article in the ENGINE
PERFORMANCE Section. For specifications, see ADJUST MENT S or SPECIFICAT IONS article in the
ENGINE PERFORMANCE Section.
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Check vane airflow meter.
Check idle speed control solenoid.
Check pressure regulator control solenoid.
Check heated exhaust gas oxygen sensor.
Check engine coolant temperature sensor.
Check A/C load control solenoid.
STUMBLE/HESITATION DURING ACCELERATION
Check throttle position switch.
Check vane airflow meter.
Check canister purge solenoid.
Check heated exhaust gas oxygen sensor.
Check wide open throttle A/C (WAC) relay.
Check A/C thermostatic switch.
MISSES/SURGES
Check exhaust gas oxygen sensor.
Check throttle position switch.
Check vane airflow meter.
Check wide open throttle vacuum switch.
Check A/C load control solenoid.
Check engine coolant temperature sensor.
IDLE IS FAST/SLOW RETURN TO IDLE
Check idle speed control solenoid.
Check by-pass air control valve.
Check engine coolant temperature sensor.
Check A/C load control solenoid.
IDLE IS ROUGH
Check idle speed control solenoid.
Check A/C load control solenoid.
Check by-pass air control valve.
Check throttle position switch.
Check vane airflow meter.
Check vane air temperature sensor.
Check canister purge solenoid.
Check engine cooling fan.
Check headlight switch.
Check blower control switch.
Check A/C thermostatic switch.
Check neutral safety switch.
Check neutral gear switch or clutch engage switch.
Check heated exhaust gas oxygen sensor.
ENGINE SPEEDS UP
Check idle speed control solenoid.
Check heated exhaust gas oxygen sensor.
Check by-pass air control valve.
CRANKS NORMALLY/NO START
Verify secondary ignition spark is present.
Verify fuel pressure is within specification.
Check vane airflow meter.
Check engine coolant temperature sensor.
CRANKS NORMALLY/SLOW TO START
Check ignition module.
Check engine coolant temperature sensor.
Check vane airflow meter.
Check evaporative emission control components.
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POOR FUEL ECONOMY
Verify intake air is not restricted.
Verify fuel pressure is within specification.
Check ignition module.
Check canister purge solenoid.
Check vane air temperature sensor.
Check vane airflow meter.
Check heated exhaust gas oxygen sensor.
EXHAUST SMOKE/ODOR
Check vane air temperature sensor.
Check vane airflow meter.
Check exhaust gas oxygen sensor.
FUEL ODOR/LEAKS
Check evaporative emission control components.
Check rollover vent valve.
Check by-pass air control valve.
FAILS EMISSION TEST
Check canister purge solenoid.
Check pressure regulator control solenoid.
Check heated exhaust gas oxygen sensor.
Check by-pass air control valve.
INTERMITTENTS
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplicating circuit or component failure to identify problem. These procedures may lead to computer setting
a fault code (on some systems) which may help in diagnosis.
If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions
causing intermittent fault. A status change on DVOM indicates a fault has been located.
Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ign it io n
switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test
procedures indicate area of fault.
TEST PROCEDURES
INTERMITTENT SIMULATION
To reproduce conditions creating an intermittent fault, use following methods:
Lightly vibrate component.
Heat component.
Wiggle or bend wiring harness.
Spray component with water.
Remove/apply vacuum source.
Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test
results to identify a faulty component or circuit.
Copyr ight 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.
Article GUID: A00022699
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E - T HEORY/OPERAT ION
1991 ENGINE PERFORMANCE Ford/Mercury T heory & Operation
INTRODUCTION
This article covers basic description and operation of engine performance-related systems and components. Read this article before attempting
to diagnose systems with which you are not completely familiar.
COMPUTERIZED ENGINE CONTROLS
An electronic Control Assembly (ECA) receives and processes signals from various sensors and switches. See Fig. 1 . It then generates signals
which control ignition timing, fuel injection functions and various emission control devices. The ECA has system diagnostic capabilities and
will store trouble codes for use by service technicians.

Fig. 1: Identifying Input Devices & Output Signals (Not All Shown)

Courtesy of FORD MOTOR CO.
ELECTRONIC CONTROL ASSEMBLY (ECA)
The ECA is located under the instrument panel on the driver side. It receives and processes data from sensors, switches and other components.
The ECA generates output signals to control fuel injection, spark timing, other engine functions and emission systems.
CEC INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input device usage of
a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article. The available input devices include the following:
BAROMETRIC PRESSURE SENSOR (BP)
This device senses changes in barometric pressure. The ECA uses this information in calculating fuel metering, ignition timing and idle speed.
On Festiva, BP is incorporated into the ECA. On Capri, BP is located on the passenger-side cowl.
BRAKE ON-OFF (BOO) SWITCH
This switch, located at the brake pedal, senses brake operation. The ECA uses this information in calculating fuel metering.
NOTE:Com ponents are grouped into 2 categories. T he first category is CEC INPUT DEVICES, which control or
produce voltage signals m onitored by the control unit. T he second category is CEC OUT PUT SIGNALS,
which are com ponents controlled by the control unit.
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