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CHART A-3

(Page 2 of 3)

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

3.8LTURBO “G” SERIES (PORT)

1986/87 Turbo Regal Ignition Circuit

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.

  1. Verifies ignition feed voltage at terminal "P" of the C3I module. Less than battery voltage would be an indication of a CKT 439 fault. 
  2. The test light to 12 volts simulates a reference signal to the ECM which will result in an injector test light blink if the CKT 430, the ECM and the injector driver circuit are all OK. 
  3. If the Cam Sensor signal circuit terminal "B" is momentarily jumpered to the ground circuit terminal "C" and the engine is cranked, without turning the ignition switch "OFF", the response should be an injector test light blink. This is a result of the artificial "Cam Signal" being transmitted through the C3I module to ECM terminal "A11" and the ECM activating the injector driver circuit.
  4. Verifies a proper Cam signal circuit voltage of 6 to 9 volts and a good ground from the C3I module to terminal NC" of the sensor connector.
  5. Determines if reason for incorrect voltage reading was due to a fault in CKT 633, an open in CKT 632 or a faulty C3I module.
  From Chart A-3 Page 1
Test light on		                                          
                                Module & coil assembly (top view) Module & coil assembly (top view)    
  │                                      
7  •Disconnect C3I module 14-pin connector.
 •Ignition on, check voltage at harness terminal "P".
 •Reading should be approx. battery voltage. Is it?		                        
                             
  ├─ ── ── ── ── ── ── ── ── ─┐                            
  Yes                 No                            
  │                 │                            
8  •Ignition on, connect a test light to 12 volts and repeatedly touch to C3I module harness term. "C".
 •Injector test light installed in any injector harness. connector should blink with each touch. Does it?		   Open in ignition feed CKT 439.                        
                           
                                 
  ├─ ── ── ── ── ── ── ── ── ── ── ── ── ─┐                    
  Yes     From Step #1 for code 41           No                    
  │     ê                   │                    
9  •Reconnect 14-pin C3I module connector.
 •Disconnect cam sensor connector.
 •Ignition on.            SEE CAUTION
 •Momentarily jumper cam sensor harness terms. "B" to "C".
 •Ignition still on, crank engine. Inj. test light should blink. Does it?		        •Check injector driver circuit from ECM for open or short to voltage.
 •Is circuit OK?		      
             
        │                    
        │                    
  ├─  ── ── ── ── ── ── ─┐           ├─ ── ── ── ── ─┐          
  No             Yes           Yes         No          
  │             │           │         │          
10  •Check voltage between cam sensor harness terms. "B" and "C".
  •Voltage should be 6-9 volts. Is it?		    •Check voltage at cam sensor harness term. "A".
 •Should be over 10 volts. Is it?		   Check CKT 430 for open or short to ground or voltage. If CKT 430 is OK, it's poor connection at ECM term. "B5" or faulty ECM.   Repair injector driver circuit.        
               
                   
  ├─ ── ── ── ─┐     ├  ── ── ── ─┐                
  No       Yes     No       Yes                        
  │       │     │       │                        
11  •Check voltage from cam sensor harness term. "B" to ground.
 •Reading should be 6 to 9 volts. Is it?		   See Page 3 of this chart   Check for open power feed CKT 631. If ckt. is ok, it's faulty C3I module connection or module.   Verify that cam sensor interrupter is turning while cranking engine. If OK, it's faulty cam sensor connection or cam sensor.*                  
                         
                             
                             
                                           
  ├─ ── ── ── ── ── ── ── ─┐           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.          
  No               Yes                    
  │               │                    
  Check CKT 633 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 CKT 632 for open. If ckt. is ok, it's faulty 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

 

Excerpt from 1987 Buick Service Manual
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