Ford Festiva. Instruction — part 47

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
voltage is 10-12 volts, repair short to voltage.

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

Circuit

ECA Pin

BOB Pin

Wire Color

1.3L

SIGRTN

2D

46, 49

BLK

VREF

2K

26

WHT/BLK

1.6L

SIGRTN

2C

46

BLU/YEL

VREF

2A

26

WHT/BLK

If no hard codes, or only pass codes, are present, and driveability symptoms or intermittent codes still exist, proceed to TESTS W/O CODES
article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic
procedures.

Copyright 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.

Article GUID: A00022768

Back To Article

H - TESTS W/O CODES

1991-92 ENGINE PERFORMANCE Ford Motor Co. Trouble 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.



Idle is rough.



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:

Some driveability problems may have been corrected by manufacturer with a revised computer
calibration chip or computer control unit. Check with manufacturer for latest chip or computer
application.

NOTE:

For specific testing procedures, see SYSTEM/COMPONENT TESTS article in the ENGINE
PERFORMANCE Section. For specifications, see ADJUSTMENTS or SPECIFICATIONS article in the
ENGINE PERFORMANCE Section.



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.