Engine Cranks But Won't Run - '86/'87 3.8L Turbo

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CHART A-3

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ENGINE CRANKS BUT WON’T RUN “TYPE I C³I”

3.8LTURBO “G” SERIES (PORT)

Circuit Description:

For timing of spark plug firing, a cam sensor 'hall effect" switch is used. The cam sensor sends a signal (Sync-Pulse) to the ignition module when cylinder #1 is 25º after top dead center on the compression stroke. This signal is used to start the correct coil firing sequence and to enable sequential fuel injection. The engine will continue to run if the cam signal is lost while running, however, will not restart after shut down and a Code 41 will be stored.

The crank sensor sends a signal to the ignition module and then to the ECM for reference rpm and crankshaft position. There are three windows in a disc (interrupter) which is mounted to the harmonic balancer. These windows pass by the sensor and as each window passes, the next coil is triggered.

Test Description:

Step numbers refer to step numbers on diagnostic chart.

Jumpering the Crank Sensor harness terminals "B" and "C" together simulates a Cam signal to the C³I module. Then, by repeatedly jumping the Crank Sensor harness terminals "B" and "C" together, a Crank signal is simulated which should result in the injector test light blinking.
Verifies a proper Crank signal circuit voltage of 6 to 9 volts and a good ground from the C³I module to terminal "B" of the sensor connector.
Determines if reason for incorrect voltage reading was due to a fault in CKT 643, an open in CKT 642 of a faulty C³I module.

From Chart A-3 Page 2
No injector test light flash

│ Module & coil assembly (top view)

12 •Ignition on and injector test light still in place.
•Momentarily jumper cam sensor harness connector (gray) terminals "B" to "C".
•Repeatedly jumper crank sensor harness connector (black) terminals "B" to "C". SEE CAUTION¶
•Injector test light should flash each time the crank sensor harness terminals are jumpered. Did it?

├─ ── ── ── ── ── ── ── ── ── ── ── ─┐

No Yes

│ │

13 •Check voltage between crank sensor harness terms. "B" and "C".
•Voltage should be 6-9 volts. Is it? •Check voltage at crank sensor harness terminal "A".
•Voltage should be over 10 volts. Is it?

├─ ── ── ── ── ─┐

No Yes ├─ ── ── ── ─┐

│ │ No Yes

14 •Check voltage between crank sensor harness term. "C" and ground.
•Voltage should be 6-9 volts. Is it? It's faulty C³I module connection or module. │ │

Check power feed CKT 641 for open or short to ground. If CKT is OK, it's C³I module connection or module. It's crank sensor connection or sensor. *

├─ ── ── ── ── ─┐

No Yes

│ │ ¶CAUTION: When jumping sensor terminals, be sure to keep fingers clear of pulleys and belts as a slight movement of belt may occur, resulting in possible injury.

Check CKT 643 for open or short to ground (if voltage was above 9 volts, check for a short to voltage and the possibility of a damaged sensor.) If ckt. is OK, it's C³I module connection or module. Check for open in ground CKT 642. If ckt. is OK, it's C³I module connection or module.

* Inspect crank sensor for proper gap (approx. .025"), or signs of rubbing. If rubbing is evident, determine cause and replace sensor.
Clear codes and confirm "Closed Loop" operation and no "Service Engine Soon" light.

11-25-86