Jeep Wrangler TJ. Manual - part 98

TEST

ACTION

APPLICABILITY

NOTE: Check for any TSBs that apply to a Misfire condition. Review the
vehicle repair history for any misfire condition repairs that have been
performed.
Read and record the FREEZE FRAME DATA. Select OBD II MONITORS. Read and
record the MIS-FIRE SIMILAR CONDITIONS WINDOW DATA.
With these screens, attempt to duplicate the condition(s) that has set this DTC.
When the vehicle is operating in the SIMILAR CONDITIONS WINDOW, refer to the
WHICH CYLINDER IS MISFIRING screen.
Observe the WHICH CYLINDER IS MISFIRING screen for at least one minute.
Is there a misfire present?

All

Yes

→ Go To 2

→ Refer to the INTERMITTENT CONDITION Symptom (Diagnos-

tic Procedure).
Perform POWERTRAIN VERIFICATION TEST VER - 5.

NOTE: Anything that affects the speed of the crankshaft can cause a misfire
DTC.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will
shut down that cylinders Injector Control circuit.
- Visually inspect the engine for any of the following conditions.
- Worn serpentine belt
- Binding Engine-Driven accessories: A/C Compressor, P/S Pump, Water pump.
- Misalignment Water pump, P/S Pump and A/C Compressor pulleys
- Corroded PCM power and ground circuits.
- Improper CKP, CMP, MAP, and TP Sensor mounting
- Poor connector/terminal to component connection. i.e., CKP sensor, Fuel Injector,
Ign coil, etc.
- Vacuum leaks
- Restricted Air Induction system or Exhaust system.
- Internal engine component failures.
Were any of the above conditions present?

All

Yes

→ Repair as necessary.

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 3

Turn the ignition off.
Disconnect the Ignition Coil harness connector and Fuel Injector harness connector
of the cylinder being tested.
Ignition on, engine not running.
With the DRBIII

t, actuate the ASD Relay.

Using a 12-volt test light connected to ground, probe the (F142), (K334) ASD Relay
Output circuit at the Ignition Coil harness connector and Fuel Injector harness
connector.
Does the test light illuminate brightly?

All

Yes

→ Go To 4

→ Repair the excessive resistance or short to ground in the (F142),

(K334) ASD Relay Output circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.

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TEST

ACTION

APPLICABILITY

Turn the ignition off.
Remove the Ignition Coil.
Connect the Ignition Coil harness connector.
NOTE Before continuing, inspect the Ignition Coil for the following condi-
tions. If a problem is found, replace the Ignition Coil. Damage or Carbon
Tracking on the Coil or the spark plug insulator boot.
Install a spark tester on the Ignition Coil.
While cranking the engine observe the spark coming from the spark tester.
NOTE: A crisp blue spark that is able to jump the gap of the spark tester
should be generated.
Is good spark present?

All

Yes

→ Go To 5

→ Go To 14

NOTE: Connect the Fuel Injector harness connector before continuing.

Turn the ignition off.
Remove the Spark Plug.
Inspect the Spark Plug for the following conditions.
- Cracks
- Carbon Tracking
- Foreign Material
- Gap size out of specifications
- Loose or broke electrode
NOTE: Lightly tap the bottom of the spark plug on a solid surface. The
electrode in the spark plug should not move.
Were any of the above condition present?

All

Yes

→ Replace the Spark Plug.

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 6

Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Install a fuel pressure gauge.
Start the engine and observe the fuel pressure reading.
NOTE: Fuel pressure specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).
Choose a conclusion that best matches your fuel pressure reading.

All

Within Specification

Go To

Below Specification

Go To

Above Specification

Replace the fuel filter/pressure regulator.
Perform POWERTRAIN VERIFICATION TEST VER - 5.

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TEST

ACTION

APPLICABILITY

NOTE: Before continuing visually and physically inspect the fuel delivery
system for external leaks or damage. Repair /replace as necessary.
Turn the ignition off.
WARNING: The fuel system is under a constant pressure even with the
engine off. Before testing or servicing any fuel system hose, fitting or line,
the fuel system pressure must be released.
Install special tool #6539 (5/16

9) or #6631 (3/89) fuel line adapter.

Install the fuel pressure gauge.
Start the engine and allow the fuel system to reach maximum pressure.
Turn the ignition off.
NOTE: Fuel specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).
Using special tool #C4390, Hose Clamp Pliers, pinch the rubber fuel line between the
fuel pressure gauge and the engine.
Monitor the fuel pressure gauge for a minimum of 5 minutes.
NOTE: The pressure should not fall below 241 KPa (35 psi)
Does the Upstream gauge fall below the above specification?

All

Yes

→ Replace the leaking Fuel Injector(s).

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 8

Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
CAUTION: After each Fuel Injector actuation, start the engine to clean the
cylinder of fuel. Failure to do so could cause engine damage.
Remove special tool #C4390.
Start the engine and allow the fuel pressure to reach maximum pressure.
Ignition on, engine not running.
Using the DRBIII

t, actuate the Fuel Injector for the cylinder that indicated the

misfire.
Monitor the fuel pressure gauge.
Does the fuel pressure gauge indicate a drop in fuel pressure?

All

Yes

→ Go To 9

→ Go To 10

NOTE: Turn the ignition off, remove the Fuel Pressure gauge, and connect
the fuel lines before continuing.

Check for any of the following conditions/mechanical problems.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
CAM LOBES - must not be worn excessively
CYLINDER LEAKAGE TEST - must be within specifications
VALVE SPRINGS - cannot be weak or broken
Are there any engine mechanical problems?

All

Yes

→ Repair as necessary.

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 16

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TEST

ACTION

APPLICABILITY

Turn the ignition off.
Disconnect the Fuel Injector harness connector.
Ignition on, engine not running.
NOTE: When a Misfire is detected for a particular cylinder, the PCM will
shut down that cylinders Injector Control circuit.
With the DRBIII

t, erase DTCs.

Using a 12-volt test light connected to 12-volts, probe the Injector Control circuit.
With the DRBIII

t, actuate the Fuel Injector.

Does the test light blink/flicker?

All

Yes

→ Replace the Fuel Injector.

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 11

Turn the ignition off.
Disconnect the C2 PCM harness connector.
CAUTION: DO NOT PROBE THE PCM HARNESS CONNECTORS. PROBING
THE PCM HARNESS CONNECTORS WILL DAMAGE THE PCM TERMI-
NALS RESULTING IN POOR TERMINAL TO PIN CONNECTION. INSTALL
MILLER SPECIAL TOOL #8815 TO PERFORM DIAGNOSIS.
Check the Injector Control circuit for an open, short to ground, and short to voltage.
Was a problem found with the Injector Control circuit?

All

Yes

→ Repair the excessive resistance or short to ground in the Injector

Control circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 16

Turn the ignition off.
Warning: The fuel system is under a constant pressure (even with the engine
off). Before testing or servicing any fuel system hose, fitting or line, the fuel
system pressure must be released.
Raise vehicle on hoist, and disconnect the fuel pressure line at the fuel pump module.
Install special tool #6539 (5/16

9) #6631(3/89) fuel line adapter and the fuel pressure

gauge between the fuel supply line and the fuel pump module.
Ignition on, engine not running.
With the DRBIII

t, actuate the ASD Fuel System test and observe the fuel pressure

gauge.
NOTE: Fuel pressure specification is 407 KPa +/- 34 KPa (59 psi +/- 5 psi).
Is the fuel pressure within specification?

All

Yes

→ Repair or replace fuel supply line as necessary.

Perform POWERTRAIN VERIFICATION TEST VER - 5.

→ Go To 13

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