coolant temperature ACURA TL 1995 Service Repair Manual

22. Remove the positive crankcase ventilation (PCV)

hose.

23. Remove the bolt securing the automatic transmis-

sion fluid (ATF) dipstick tube bracket.

6 x 1.0 mm

12 N-m (1.2 kgf-m,

8.7 Ibf-ft)

ATF BRACKET

DIPSTICK TUBE

BRACKET

PCV HOSE

24.

Remove the engine wire harness connectors and

wire harness clamps from the cylinder heads and

intake manifold.

Six injector connectors

Six ignition coil connectors

Throttle position sensor connector

CKP/CYP sensor connector

Intake air temperature (IAT) sensor connector

Exhaust gas recirculation (EGR) valve lift sensor

connector

Idle air control (IAC) valve connector

Engine coolant temperature (ECT) sensor con-

nector

ECT gauge sending unit connector

Engine oil temperature sensor connector

Left primary heated oxygen sensor (left primary

HO2S) connector

Right primary heated oxygen sensor (right pri-

mary HO2S) connector

Evaporative emission (EVAP) purge control

solenoid valve connector ('97 - '98)
25. Remove the inlet pipe mounting bolts from the right

cylinder head cover.

26. Remove the vacuum hoses and breather hose.

6 x 1.0 mm

12 N-m (1.2 kgf-m, 8.7 Ibf-ft)

BREATHER

HOSE

VACUUM

HOSES

27. Remove the six ignition coils from the left and right

cylinder head covers.

6 x 1.0 mm

12 N-m (1.2 kgf-m, 8.7 Ibf-ft)

IGNITION

COILProCarManuals.com

Thermostat

Replacement

NOTE: Use new O-rings when reassembling.

ENGINE COOLANT

TEMPERATURE

(ECT) SENSOR

18 N-m (1.8 kgf-m, 13 Ibf-ft)
BLEED BOLT

9.8 N-m (1.0 kgf-m,

7.2 Ibf-ft)

O-RING

Replace.
ECT GAUGE

SENDING UNIT

9 N-m (0.9 kgf-m,

7lbf-ft)

THERMOSTAT

COVER

THERMOSTAT

Install with pin up.

RUBBER SEAL

Replace.

6 x 1.0 mm

12 N-m (1.2 kgf-m,

8.7 Ibf-ft)ProCarManuals.com

PGM-FI System

System Description (cont'd)

3. Fuel Cut-off Control

During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at

speeds over 1,000 rpm.

Fuel cut-off action also takes place when engine speed exceeds 6,500 rpm, regardless of the position of the throttle

valve, to protect the engine from over-revving.

4. A/C Compressor Clutch Relay .

When the PCM receives a demand for cooling from the air conditioning system, it delays the compressor from being

energized, and enriches the mixture to assure a smooth transition to the A/C mode.

5. Evaporative Emission (EVAP) Purge Control Solenoid Valve

'96 model: When the engine coolant temperature is below 158°F (70°C), the PCM controls the EVAP purge control

solenoid valve which cuts vacuum to the EVAP purge control canister diaphragm.

'97 - 98 models: When the engine coolant temperature is above 99°F (37°C), the PCM controls the EVAP purge control

solenoid valve which controls vacuum to the EVAP purge control canister.

6. Intake Air Bypass (IAB) Low Control Solenoid Valve, Intake Air Bypass (IAB) High Control Solenoid Valve

When engine speed is below 3,350 rpm, the IAB High Control Solenoid Valve and IAB Low Control Solenoid Valve are

activated by a signal from the PCM. Intake air flows through a long chamber path, increasing torque at low RPM.

When engine speed is 3,350 - 3,950 rpm, the IAB Low Control Solenoid Valve is deactivated by the PCM. Intake air

flows through a short chamber path, increasing mid-range torque.

When the engine rpm is above 3,950 rpm, the IAB Low Control Solenoid Valve and IAB High Control Solenoid Valve are

deactivated by the PCM. This creates a very short intake path and increases high-speed torque.

7. Exhaust Gas Recirculation (EGR) Control Solenoid Valve

When the EGR is required for control of oxides of nitrogen (NOx) emissions, the PCM controls the EGR control solenoid

valve which supplies regulated vacuum to the EGR valve.

ECM Fail-safe/Back-up Functions

1. Fail-safe Function

When an abnormality occurs in a signal from a sensor, the PCM ignores that signal and assumes a pre-programmed

value for that sensor that allows the engine to continue to run.

2. Back-up Function

When an abnormality occurs in the PCM itself, the fuel injectors are controlled by a back-up circuit independent of the

system in order to permit minimal driving.

3. Self-diagnosis Function [Malfunction Indicator Lamp (MIL)]

When an abnormality occurs in a signal from a sensor, the PCM supplies ground for the MIL and stores the DTC in

erasable memory. When the ignition is initially turned on, the PCM supplies ground for the MIL for two seconds to

check the MIL bulb condition.

4. Two Driving Cycle Detection Method

To prevent false indications, the two driving cycle detection method is used for the H02S, fuel metering-related, idle

control system, ECT sensor, EGR system, TWC, EVAP control system and other self-diagnostic functions. When an

abnormality occurs, the PCM stores it in its memory. When the same abnormality recurs after the ignition switch is

turned OFF and ON (II) again, the PCM informs the driver by lighting the MIL.

However, to ease troubleshooting, this function is cancelled when you short the service check connector. The MIL will

then blink immediately when an abnormality occurs.ProCarManuals.com

Evaporative Emission (EVAP) Controls

Description

The evaporative emission controls are designed to minimize the amount of fuel vapor escaping to the atmosphere. The

system consists of the following components:

A. Evaporative Emission (EVAP) Control Canister

An EVAP control canister is used for the temporary storage of fuel vapor until the fuel vapor can be purged from the

EVAP control canister into the engine and burned.

B. Vapor Purge Control System

EVAP control canister purging is accomplished by drawing fresh air through the EVAP control canister and into a port

on the throttle body. The purging vacuum is controlled by the EVAP purge control solenoid valve.

'96 model:
'97 - 98 models:

C. Fuel Tank Vapor Control System

When fuel vapor pressure in the fuel tank is higher than the set value of the EVAP two way valve, the valve opens and

regulates the flow of fuel vapor to the EVAP control canister.

'96 model:

INTAKE MANIFOLD
THROTTLE

BODY

EVAP PURGE

CONTROL

SOLENOID VALVE

FUEL TANK

EVAP VALVE
EVAP TWO WAY VALVE
From

No. 4 ECU
(PCM) (15A)

FUSE (in the under-dash

fuse/relay box)

EVAP

CONTROL

CANISTER FRESH

AIR
EVAP PURGE

FLOW SWITCH

FUEL FILL CAP
PCM
VARIOUS

SENSORS

FUEL TANK
ENGINE COOLANT TEMPERATURE ABOVE 158°F (70°C)
ENGINE COOLANT TEMPERATURE ABOVE 99°F (37°C)
EVAP PURGE CONTROL SOLENOID VALVE DUTY CON-

TROLLED AFTER STARTING ENGINE
EVAP PURGE CONTROL SOLENOID VALVE OFF AFTER

STARTING ENGINEProCarManuals.com

Grade Logic Control System

How it works:

The PCM compares actual driving conditions with driving conditions memorized in the PCM, based on the input from the

vehicle speed sensor, throttle position sensor, engine coolant temperature sensor, barometric pressure sensor, brake

switch signal and shift lever position signal, to control shifting while a vehicle is ascending or descending a slope, or

reducing speed.

(cont'd)ProCarManuals.com

Cylinder Head

Removal (cont'd)

17. Remove the spark plug wires, distributor and ground

cables from the cylinder head.

O-RING

Replace.
8 x
1.25
mm

18 N-m (1.8 kgf-m,

13 Ibf-ft)

DISTRIBUTOR

GROUND

CABLES

18. Remove the wire harness covers and positive crank-

case ventilation (PCV) hose.

6 x 1.0 mm

9.8 N-m (1.0 kgf-m,

7.2 Ibf-ft)

PCV HOSE

WIRE HARNESS

COVERS

6 x 1.0 mm

12 N-m (1.2 kgf-m, 8.7 Ibf-ft)
19. Remove the engine wire harness connectors and

wire harness clamps from the cylinder head and the

intake manifold.

• Five injector connectors

• TDC/CKP/CYP sensor connector

• CKF sensor connector

• Idle air control (IAC) valve connector

• Engine coolant temperature (ECT) sensor connec-

tor

• ECT gauge sending unit connector

• ECT switch connector

• Exhaust gas recirculation (EGR) valve lift sensor

connector

• Throttle position sensor connector

• Intake air bypass (IAB) control solenoid valve con-

nector

• Evaporative emission (EVAP) purge control sole-

noid valve connector

20. Remove the ground cable and water bypass hose.

GROUND

CABLE

6 x 1.0 mm

12 N-m (1.2 kgf-m, 8.7 Ibf-ft)

WATER BYPASS

HOSEProCarManuals.com

System Description

Vacuum Connections (cont'd)

'95 - 96 models:

PRIMARY HEATED OXYGEN SENSOR (PRIMARY HO2S)

SECONDARY HEATED OXYGEN SENSOR (SECONDARY

HO2S)

MASS AIR FLOW (MAP) SENSOR

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

INTAKE AIR TEMPERATURE (IAT) SENSOR

FRONT KNOCK SENSOR (FKS)

REAR KNOCK SENSOR (RKS)

IDLE AIR CONTROL (IAC) VALVE

FAST IDLE THERMO VALVE

IDLE ADJUSTING SCREW

THROTTLE BODY (TB)

FUEL INJECTOR

FUEL FILTER

FUEL PRESSURE REGULATOR

FUEL PULSATION DAMPER

FUEL PUMP (FP)

FUEL TANK

FUEL TANK EVAPORATIVE EMISSION (EVAP) VALVE

AIR CLEANER

RESONATOR

CRANKSHAFT SPEED FLUCTUATION (CKF) SENSOR

INTAKE AIR BYPASS (IAB) CHECK VALVE
INTAKE AIR BYPASS (IAB) VACUUM TANK

INTAKE AIR BYPASS (IAB) CONTROL SOLENOID VALVE

INTAKE AIR BYPASS (IAB) CONTROL DIAPHRAGM

EXHAUST GAS RECIRCULATION (EGR) VACUUM CONTROL

VALVE

EXHAUST GAS RECIRCULATION (EGR) CONTROL

SOLENOID VALVE

EXHAUST GAS RECIRCULATION (EGR) VALVE

EXHAUST GAS RECIRCULATION (EGR) VALVE LIFT

SENSOR

POSITIVE CRANKCASE VENTILATION (PCV) VALVE

EVAPORATIVE EMISSION (EVAP) PURGE CONTROL

SOLENOID VALVE

EVAPORATIVE EMISSION (EVAP) PURGE FLOW SWITCH

EVAPORATIVE EMISSION (EVAP) CONTROL CANISTER

EVAPORATIVE EMISSION (EVAP) PURGE CONTROL

DIAPHRAGM VALVE

EVAPORATIVE EMISSION (EVAP) TWO WAY VALVE

WARM UP THREE WAY CATALYTIC CONVERTER (WU TWC)

THREE WAY CATALYTIC CONVERTER (TWC)

WATER VALVE CONTROL SOLENOID VALVE

WATER VALVE CONTROL DIAPHRAGM

WATER VALVE CHECK VALVEProCarManuals.com

'97 - 98 models:

Vacuum hose No.

PRIMARY HEATED OXYGEN SENSOR (PRIMARY HO2S)

SECONDARY HEATED OXYGEN SENSOR (SECONDARY

HO2S)

MASS AIR FLOW (MAP) SENSOR

ENGINE COOLANT TEMPERATURE (ECT) SENSOR

INTAKE AIR TEMPERATURE (IAT) SENSOR

FRONT KNOCK SENSOR (FKS)

REAR KNOCK SENSOR (RKS)

IDLE AIR CONTROL (IAC) VALVE

FAST IDLE THERMO VALVE

IDLE ADJUSTING SCREW

THROTTLE BODY (TB)

FUEL INJECTOR

FUEL FILTER

FUEL PRESSURE REGULATOR

FUEL PULSATION DAMPER

FUEL PUMP (FP)

FUEL TANK

FUEL TANK EVAPORATIVE EMISSION (EVAP) VALVE

AIR CLEANER

RESONATOR

CRANKSHAFT SPEED FLUCTUATION (CKF) SENSOR

INTAKE AIR BYPASS (IAB) CHECK VALVE

INTAKE AIR BYPASS (IAB) VACUUM TANK

INTAKE AIR BYPASS (IAB) CONTROL SOLENOID VALVE
INTAKE AIR BYPASS (IAB) CONTROL DIAPHRAGM

EXHAUST GAS RECIRCULATION (EGR) VACUUM CONTROL

VALVE

EXHAUST GAS RECIRCULATION (EGR) CONTROL

SOLENOID VALVE

EXHAUST GAS RECIRCULATION (EGR) VALVE

EXHAUST GAS RECIRCULATION (EGR) VALVE LIFT

SENSOR

POSITIVE CRANKCASE VENTILATION (PCV) VALVE

EVAPORATIVE EMISSION (EVAP) PURGE CONTROL

SOLENOID VALVE

EVAPORATIVE EMISSION (EVAP) CONTROL CANISTER

EVAPORATIVE EMISSION (EVAP) CONTROL CANISTER

VENT SHUT VALVE

EVAPORATIVE EMISSION (EVAP) THREE WAY VALVE

EVAPORATIVE EMISSION (EVAP) TWO WAY VALVE

EVAPORATIVE EMISSION (EVAP) BYPASS SOLENOID

VALVE

FUEL TANK PRESSURE SENSOR

WARM UP THREE WAY CATALYTIC CONVERTER (WU TWC)

THREE WAY CATALYTIC CONVERTER (TWC)

WATER VALVE CONTROL SOLENOID VALVE

WATER VALVE CONTROL DIAPHRAGM

WATER VALVE CHECK VALVEProCarManuals.com

Troubleshooting

Troubleshooting Procedures (cont'd)

ECM Data

By connecting the OBD II scan tool or the Honda PGM Tester to the 16P data link connector (DLC), various data can be

retrieved from the ECM. The items listed in the table below conform to the SAE recommended practice.

The Honda PGM Tester also reads data beyond that recommended by SAE.

Understanding this data will help to find the causes of intermittent failures or engine problems.

NOTE:

• The "operating values" given below are approximate values and may be different depending on the environment and

the individual vehicle.

• Unless noted otherwise, "at idle speed" means idling with the engine completely warmed up, the transmission in posi-

tion or , and the A/C and all accessories turned off.

Data
Description
Operating Value

Freeze Data

Diagnostic

Trouble Code

(DTC)
If the ECM detects a problem, it will store it as a code

consisting of one letter and four numbers.

Depending on the problem, an SAE-defined code

(P0xxx)
or a
Honda-defined code
(P1xxx)
will
be
output

to the tester.
If no problem is detected,

there is no output.

Engine Speed

The ECM computes engine speed from the signals sent

from the Crankshaft Position sensor.

This data is used for determining the time and amount

of fuel injection.
Nearly the same as

tachometer indication

At idle speed:

700 ± 50 rpm

Vehicle Speed

The ECM converts pulse signals from the Vehicle

Speed Sensor (VSS) into speed data.
Nearly the same as

speedometer indication

Mass Air

Flow (MAF)
The MAF sensor measures the volume of the air that

flows into the engine, and sends voltage signals to the

ECM.
At idle speed:

2.2 - 4.4 g/sec

At 2,500 rpm with not

load:

7.5- 13.0 g/sec

Engine Coolant

Temperature

(ECT)
The ECT sensor converts coolant temperature into

voltage and signals the ECM. The sensor is a thermistor

whose internal resistance changes with coolant

temperature. The ECM uses the voltage signals from

the ECT sensor to determine the amount of injected

fuel.
With cold engine:

Same as ambient temper-

ature and IAT

With engine warmed up:

90 - 96°C

Heated Oxygen

Sensor (HO2S)

(Primary)

(Secondary)
The Heated Oxygen Sensor detects the oxygen content

in the exhaust gas and sends voltage signals to the

ECM. Based on these signals, the ECM controls the

air/fuel ratio. When the oxygen content is high (that is,

when the ratio is leaner than the stoichiometric ratio),

the voltage signal is lower. When the oxygen content is

low (that is, when the ratio is richer than the stoichio-

metric ratio), the voltage signal is higher.
0.0-1.25V

At idle speed:

about 0.1-0.9VProCarManuals.com

PGM-FI System

System Description

INPUTS
ENGINE CONTROL MODULE (ECM)

OUTPUTS

Fuel Injectors

PGM-FI Main Relay (Fuel Pump)

MIL

IAC Valve

A/C Compressor Clutch Relay

Radiator Fan Relay

Condenser Fan Relay

ALT

ICM

EVAP Purge Control Solenoid

Valve

Primary HO2S Heater

Secondary H02S Heater

EGR Control Solenoid Valve

IAB Control Solenoid Valve

EVAP Bypass Solenoid Valve*2

EVAP Control Canister Vent Shut

Valve*2

*1: '95-96 models

*2: '97 - 98 models

PGM-FI System

The PGM-FI system on this model is a sequential multiport fuel injection system.

Fuel injector Timing and Duration

The ECM contains memories for the basic discharge durations at various engine speeds and manifold air flow rates. The

basic discharge duration, after being read out from the memory, is further modified by signals sent from various sensors

to obtain the final discharge duration.

Idle Air Control

Idle Air Control Valve (IAC Valve)

When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is depressed, the P/S load

is high, or the alternator is charging, the ECM controls current to the IAC Valve to maintain the correct idle speed.

Ignition Timing Control

• The ECM contains memories for basic ignition timing at various engine speeds and manifold air flow rates. Ignition

timing is also adjusted for engine coolant temperature.

• A knock control system is also used. When detonation is detected by a knock sensor (KS), the ignition timing is retarded.

Other Control Functions

1. Starting Control

When the engine is started, the ECM provides a rich mixture by increasing fuel injector duration.

2. Fuel Pump Control

• When the ignition switch is initially turned on, the ECM supplies ground to the PGM-FI main relay that supplies

current to the fuel pump for two seconds to pressurize the fuel system.

• When the engine is running, the ECM supplies ground to the PGM-FI main relay that supplies current to the fuel pump.

• When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts

current to the fuel pump.

3. Fuel Cut-off Control

• During deceleration with the throttle valve closed, current to the fuel injectors is cut off to improve fuel economy at

speeds over 1,250 rpm.

• Fuel cut-off action also takes place when engine speed exceeds 7,100 rpm, regardless of the position of the throttle

valve, to protect the engine from over-revving.
CKP/TDC/CYP Sensor

CKF Sensor

MAF Sensor

ECT Sensor

IAT Sensor

TP Sensor

EGR Valve Lift Sensor

Primary HO2S

Secondary H02S

VSS

BARO Sensor

ELD

Front KS

Rear KS

Starter Signal

ALT FR Signal

Air Conditioning Signal

A/T Gear Position Signal

Battery Voltage (IGN.1)

Brake Switch Signal

PSP Switch Signal

EVAP Purge Flow Switch*1

Fuel Tank Pressure Sensor*2ProCarManuals.com