1991 FORD FESTIVA Engine Coolant Temperature

IGNITION SYSTEM TROUBLE SHOOTING
Open coolant temperature sensor circuitTest sensor and wiring
Shorted W.O.T. switch in T.P.S.Disconnect W.O.T. switch,
engine should start
Defective ECMReplace ECM
Fuel tank residual pressure valve leaksTest for fuel pressure drop
after shut down
Hard Starting
Disconnected hot air tube to air cleanerReconnect tube and test
control valve
Defective Idle Air Control (IAC) valveTest valve operation and
circuit
Shorted, open or misadjusted T.P.S.Test and adjust or replace
T.P.S.
EGR valve openTest EGR valve and control
circuit
Poor Oxygen sensor signalTest for shorted or circuit
Incorrect mixture from PCV systemTest PCV for flow, check
sealing of oil filter cap
Poor High Speed Operation
Low fuel pump volumeFaulty pump or restricted fuel
lines or filters
Poor MAP sensor signalTest MAP sensor, vacuum
hose and wiring
Poor Oxygen sensor signalTest for shorted or open
sensor or circuit
Open coolant temperature sensor circuitTest sensor and wiring
Faulty ignition operationCheck wires for cracks or poor
con- nections, test secondary
voltage with oscilloscope
Contaminated fuelTest fuel for water or alcohol
Intermittent ECM groundTest ECM ground connection
for resistance
Restricted air cleanerReplace air cleaner
Restricted exhaust systemTest for exhaust manifold back
pressure
Poor MAF sensor signalCheck leakage between sensor
and manifold
Poor VSS signalIf tester for ALCL hook-up is
available check that VSS
reading matches speedometer
Ping or Knock on Acceleration
Poor Knock sensor signalTest for shorted or open
sensor or circuit
Poor Baro sensor signalTest for shorted or open
sensor or circuit
Improper ignition timingSee VEHICLE EMISSION
CONTROL LABEL (where
applicable)
Check for engine overheating problemsLow coolant, loose belts or
electric cooling fan inoperative
NOTE:For additional electronic fuel injection trouble shooting inform ation, see the appropriate article in the
ENGINE PERFORMANCE section (not all vehicles have Com puter Engine Control articles). Inform ation
is provided there for diagnosing fuel system problem s on vehicles with electronic fuel injection.
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. T he purpose of this T rouble Shooting inform ation is to provide a list
of com m on causes to problem sym ptom s. For m odel-specific T rouble Shooting, refer to SUBJECT ,
DIAGNOST IC, or T EST ING articles available in the section(s) you are accessing.
Page 17 of 36 MITCHELL 1 ARTICLE - GENERAL INFORMATION Trouble Shooting - Basic Procedures
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Fig. 14: Typical Negative Backpressure EGR Valve

Courtesy of GENERAL MOTORS CORP.
Digital EGR Valve
The digital EGR valve operates independently of engine manifold vacuum. This valve controls EGR flow through 3 orifices. These 3 orifices
are opened and closed by electric solenoids. The solenoids are, in turn, controlled by the Electronic Control Module (ECM). When a
solenoid is energized, the armature with attached shaft and swivel pintle is lifted, opening the orifice. See Fig. 15
.
The ECM uses inputs from the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS) and Mass Airflow (MAF) sensors to
control the EGR orifices to make 7 different combinations for precise EGR flow control. At idle, the EGR valve allows a very small amount of
exhaust gas to enter the intake manifold. This EGR valve normally operates above idle speed during warm engine operation.
Verify EGR valve is present and not modified or purposely damaged. Ensure thermal vacuum switches, pressure transducers, speed switches,
etc., (if applicable) are not by-passed or modified. Ensure vacuum hose(s) to EGR valve is not plugged. Ensure electrical connector to EGR
valve is not disconnected.
Page 8 of 12 MITCHELL 1 ARTICLE - EMISSION CONTROL VISUAL INSPECTION PROCEDURES 1983-93 GENERAL INFORMATI
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Back To Article
SERVICE INDICATOR & WARNING LIGHTS
1988-92 MAINT ENANCE Ford Motor Co. Service Indicator & Warning Lights
SERVICE INDICATOR & WARNING LIGHTS

Fig. 1: Identifying Dash Gauges & W arning Lights

Courtesy of FORD MOTOR CO.
CHECK ENGINE WARNING LIGHT
If functioning properly, the Check Engine warning light comes on when ignition switch is in the ON position and goes out after engine is
started. If light fails to glow with ignition on or remains on when engine is running, a malfunction exists in the electronic engine control
system. System needs to be checked and serviced.
CHARGING SYSTEM WARNING LIGHT
Light comes on when ignition switch is in the ON or START position and goes out after engine is started and alternator is charged. Light may
also glow when there is a heavy electrical load on the system. If light remains on after reducing electrical load, check electrical system.
OIL PRESSURE WARNING LIGHT
Light should come on briefly and go out after engine is started. If light remains on with engine running, oil pressure is low. Check oil level.
ENGINE COOLANT TEMPERATURE GAUGE
Gauge should register within the NORMAL band under regular operating conditions. If gauge rises into the HOT range, stop engine, allow it to
cool, and then check coolant level.
BRAKE WARNING LIGHT
The Brake light indicates one of 2 conditions: parking brake is engaged, or malfunction exists in the dual braking system. If functioning
properly, light should come on briefly with ignition switch in the ON position and then go out after engine is started and parking brake is
released. If light remains on, a malfunction is indicated. Service brake system.
Copyr ight 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.
Article GUID: A00062872
Page 1 of 1 MITCHELL 1 ARTICLE - SERVICE INDICATOR & WARNING LIGHTS 1988-92 MAINTENANCE Ford Motor Co. Service
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