Circuit Description
The Engine Cranks but Does Not Run diagnostic table is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic table directs the service technician to the appropriate system diagnosis.
The Engine Cranks But Does Not Run diagnostic table assumes the following:
| • | The batteries are completely charged. Refer to Battery Inspection/Test in Engine Electrical. |
| • | The cranking speed is within specifications. Refer to Engine Cranks Slowly in Engine Electrical. |
| • | There is adequate fuel in the fuel tanks. |
Diagnostic Aids
If the cause of an engine cranks but will not run condition has not been found, inspect for the following conditions:
| • | Hard starting only in cold ambient temperatures. These may cause an intermittent condition that may not occur in the service bay: |
| - | Fuel heater inoperative, refer to Fuel Heater Inoperative . |
| - | Ice blockage at the fuel pickup in the fuel tank. This will be a high vacuum in the supply lines while cranking, and the problem will disappear after the vehicle is brought in the service bay. It may also exhibit a start and stall condition or a starting condition with no acceleration. |
| • | The correct cranking speed is 100 RPM cold and 180 RPM hot. A scan tool can be used to inspect cranking speed by pulling the ignition 1 relay and monitoring engine speed on the scan tool while cranking. |
| • | Water or foreign material in fuel system |
| • | A basic engine problem |
| • | If the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor are disconnected or malfunctioning at the same time, an Engine Cranks But Does Not Run condition will exist. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for an ignition 1 voltage supply to the engine control module (ECM).
-
This step tests the 12-volt reference circuit to the CKP sensor and the CMP sensor. The 12-volt reference circuit for the CKP sensor and the CMP sensor is connected internally within the ECM. If the 12-volt reference circuit is shorted to ground, the engine will not start and no engine speed will be indicated on the scan tool.
-
If there is fuel in the engine oil, fuel may be leaking from the fuel injector or fuel injection pump into the crankcase.
-
If the fuel system will not even briefly prime to 10 psi and will not start, the check valve in the fuel filter/heater element housing is stuck open.
-
This step determines if the fuel system is bleeding down causing a no start. The fuel pressure will slowly drop to 0 psi, but should still be above 8 psi 10 seconds after pressurizing the fuel system.
-
This step determines if the problem is a stuck open or broken fuel injector. If fuel vapors come out of any of the glow plug holes, excessive fuel is being sent into a cylinder, and not being distributed to all of the fuel injectors.
-
The engine will not run without an actual fuel rail pressure more than 10 MPa (1,450 psi).
-
If the no-start condition takes place in cold operating temperatures, 2-4°C (35-40°F) or colder, a glow plug system failure may cause the no-start condition.
-
In some cases, no compression, possibly with excessive fuel, in a single cylinder can cause a no start.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||||
2 |
Does the scan tool display DTC P0090, P0335, P0336, P0340, P0370, P0374, P0380, P0601, P0602, P0603, P0604, P0611, P0612, P1621, P1626, P1631, P1683, or U1800? | -- | Go to Step 3 | |||||||||
3 | Is the customer's concern with a fuel smell or fuel leak? | -- | Go to Fuel Leak Diagnosis | Go to Step 4 | ||||||||
4 | Observe the Actual Fuel Rail Pressure parameter with a scan tool. Is the pressure within the specified range? | 1-1.8 MPa | Go to Step 5 | Go to Step 18 | ||||||||
Observe the Ignition 1 signal parameter with a scan tool. Is the Ignition 1 signal parameter at the specified value? | B+ | Go to Step 6 | Go to Step 24 | |||||||||
Is the Engine Speed parameter more than the specified value? | 0 RPM | Go to Step 7 | Go to Step 19 | |||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 8 | |||||||||
Can you prime the system to the specified value? | 8 psi | Go to Step 9 | Go to Step 31 | |||||||||
Does the pressure measure more than the specified value for more than 2 minutes? | 2 psi | Go to Step 10 | Go to Step 13 | |||||||||
10 | Perform the Engine Compression Test. Refer to Engine Compression Test in Engine Mechanical - 6.6L. Repair the engine as necessary. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 11 | ||||||||
Did any of the cylinders emit any fuel vapor during the Engine Compression Test? | -- | Go to Step 28 | Go to Step 12 | |||||||||
Is the Actual Fuel Rail Pressure parameter more than the specified value? | 10 MPa (1,450 psi) | Go to Step 14 | Go to Step 13 | |||||||||
13 |
Does the engine start? | -- | Go to Fuel System Diagnosis | |||||||||
Observe the Glow Plug System Type parameter with a scan tool. Is the Glow Plug System Type Federal? | -- | Go to Step 15 | Go to Step 16 | |||||||||
15 |
Important: Repeat this procedure on both banks of the engine. This test may be repeated as many times as necessary.
Does the test lamp turn ON and OFF? | -- | Go to Step 16 | |||||||||
16 |
Important: If there is high resistance in the signal or low reference circuits of the crankshaft position (CKP) sensor the Engine Speed parameter of the scan tool will display a value more than 0. It will not be an accurate measure of engine speed, and can cause an Engine Cranks but does Not Run condition. Test the CKP sensor signal and low reference circuits for high resistance. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 17 | ||||||||
Inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 34 | Go to Diagnostic Aids | |||||||||
18 |
Does the Actual Fuel Rail Pressure parameter measure more than the specified value? | 175 MPa | Go to Step 23 | Go to Step 22 | ||||||||
19 |
Is the voltage more than the specified value? | 10 V | Go to Step 29 | Go to Step 20 | ||||||||
20 |
Is the voltage more than the specified value? | 10 V | Go to Step 30 | Go to Step 21 | ||||||||
21 | Test the 12-volt reference circuit of the CKP sensor and the CMP sensor for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 33 | ||||||||
22 | Test the FRP sensor signal circuit for a short to ground. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 33 | ||||||||
23 | Test the FRP sensor circuits for high resistance. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 25 | ||||||||
24 |
Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 26 | ||||||||
25 | Test for an intermittent or for a poor connection at the FRP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 32 | ||||||||
26 |
Does the engine start? | -- | Go to Step 34 | Go to Step 27 | ||||||||
27 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 34 | Go to Step 33 | ||||||||
28 |
Important: When the fuel injector pressure lines are removed, debris will fall on the fuel injector inlet fitting. Vacuum the debris from the area to prevent the debris from falling in the fuel injector. Replace the fuel injectors on the affected cylinders. Refer to Fuel Injector Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
29 | Replace the CKP sensor. Refer to Crankshaft Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
30 | Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
31 |
Important: Before replacing the fuel filter/heater element housing, inspect the fuel vent screw for damage or cross threading. Replace the vent screw w/"O" ring if either condition is found. Replace the fuel filter/heater element housing. Refer to Fuel Filter Assembly Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
32 | Replace the FRP sensor. Refer to Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
33 | Replace the engine control module (ECM). Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 34 | -- | ||||||||
34 |
Does the engine start and continue to run? | -- | Go to Step 35 | Go to Step 2 | ||||||||
35 |
Are any DTCs displayed? | -- | System OK |
