Engine Cranks But Does Not Run (LDD or LUJ)
Diagnostic Instructions
Circuit/System Description
The engine cranks but does not run is an organized approach to
identify a condition which causes the engine to crank but not
start. This diagnostic directs the technician to the appropriate
system diagnosis.
This diagnostic assumes the system voltage levels are adequate
for starter motor operation. Fuel level and fuel quality must be
determined for correct diagnosis.
Diagnostic Aids
Inspect for any of the following conditions:
• |
Insufficient fuel can cause a
no start condition. Thoroughly inspect the fuel delivery system for
sufficient fuel volume to the fuel injectors. Inspect the fuel
supply components for partial blockage or restrictions.
|
• |
Fuel injectors with partially
blocked and restricted nozzles, or a malfunctioning solenoid, can
cause a no start condition. Refer to
Fuel Injector Diagnosis . |
• |
There may be fuel spray at the
fuel injectors and the indicated fuel pressure may be correct, yet
there may not be enough fuel to start the engine. If the fuel
injectors and the injector circuit are OK, and fuel spray is
detected, the fuel injector ON time may be inadequate. If the
engine control module (ECM) receives incorrect inputs from the
various information sensors, the fuel delivered by the fuel
injectors may be inadequate to start the engine. Check all the
engine data parameters with a scan tool and compare the values
indicated with the expected values or the values from a known
vehicle in good condition. |
• |
Check the crankshaft position
sensor engine reference signal with a scan tool. Observe the engine
speed parameter while cranking the engine. The scan tool should
indicate a steady 200–300 RPM while cranking. If erratic
values, such as sudden spikes in the engine speed, are displayed,
the engine reference signal is not stable enough for the engine to
start and run properly. |
• |
Inspect the engine for good
secure electrical grounds. |
• |
If the engine almost starts
and then stalls, check for an open in the ground circuits of the
crankshaft position sensor and the camshaft position sensor –
Intake or camshaft position sensor – Exhaust. |
• |
Water or foreign material in
the fuel can cause a no start or engine will not stay running
condition. During freezing weather water can freeze inside the fuel
system. The engine may start after 30 min in a heated repair shop.
The malfunction may not recur until parked overnight in freezing
temperatures. Extreme weather conditions can cause contaminated
fuel to prevent the vehicle from starting. |
• |
A vehicle that starts and runs
after being brought to the repair shop for a no start condition,
may have an ignition system that is susceptible to moisture. Spray
water on the ignition system components and the wiring in order to
check for an engine starting or will not stay running
concern. |
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Special Tools
• |
CH 48027
Digital Pressure Gauge |
• |
EN 36012-A
Ignition System Diagnostic Harness |
• |
EL 26792 HEI
Spark Tester |
For equivalent regional tools, refer to
Special Tools .
Circuit/System Verification
Note: This diagnostic
assumes the following:
• |
The battery is
completely charged. See Battery Inspection/Test. |
• |
The engine
cranking speed is acceptable. See Engine Cranks Slowly.
|
• |
There is adequate
fuel in the fuel tank. |
Circuit/System Testing
1. |
Crank the engine for up to 15
s, observe the DTC information with a scan tool. Verify that DTC
P0117 00, P0118 00, P0122 00, P0123 00, P0222 00, P0223 00, P0335
00, P0336 00, P0513 00, P0562 00, P0563 00, P0601 00, P0602 00,
P0603 00, P0604 00, P0606 00, P062F 00, P0633 00, P0685 00, P0689
00, P0690 00, P1516 00, P1631 00, P1682 00, P16F3 00, P2101 00,
P2119 00, or P2610 00 are not set. |
2. |
Ignition ON, observe the Theft
Deterrent LED located in the driver information center. The LED
should be OFF. |
3. |
Engine cranking, observe the
scan tool Engine Speed parameter. The scan tool should indicate an
engine speed greater than 0 RPM. |
|
Note: It may be
necessary to secure the EN 36012-A Ignition System
Diagnostic Harnessto the spark plug boots with electrical tape.
|
4. |
Install the EN
36012-A Ignition System Diagnostic Harnessto the spark
plug boots. |
5. |
Connect the EL 26792
HEI Spark Testerbetween the boot of a spark plug wire and
earth. |
6. |
Connect the remaining wires to
the appropriate cylinders. |
|
Note: An erratic or
weak spark is considered a no spark condition.
|
7. |
Engine cranking, verify the
spark tester sparks. |
8. |
Ignition ON, command the fuel
pump ON with a scan tool. You should hear the fuel pump turn
ON. |
9. |
Ignition OFF, disconnect the
harness connector at a Q17 Fuel Injector. |
10. |
Connect a test lamp between
the control circuit and the ignition voltage circuit. Engine
cranking, the injector test lamp should flash. |
11. |
Ignition OFF, install the
CH 48027 Digital Pressure Gauge. |
|
Note:
• |
The fuel pump may
need to be commanded ON a few times, in order to obtain the highest
possible fuel pressure. |
• |
Do NOT start the
engine for this test. |
|
12. |
Ignition ON, command the fuel
pump ON with a scan tool. The fuel pressure should be between
365–414 kPa (53–60 PSI). |
13. |
Verify the following
conditions do not exist: |
|
• |
Collapsed air intake duct to
the throttle body |
|
• |
Air filter and air intake
system for restrictions and obstructions |
|
• |
Spark plugs for being gas or
coolant fouled |
|
• |
A skewed manifold absolute
pressure (MAP) sensor |
|
• |
A skewed engine coolant
temperature (ECT) sensor |
⇒ |
If you find any of the above conditions, repair as
necessary. |
Repair Verification
Perform the
Diagnostic Repair Verification after completing the diagnostic
procedure.
Spark Plug Replacement
|