Strange Misfires on New Engine
09-08-2012, 04:33 AM
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Staging Lane
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Strange Misfires on New Engine Just got my rebuilt LS1 back in my car and so far it is running GREAT! Motor has good response and a tail load of getty-up. Anyway, while logging data with my HP tuners, the scanner is picking up Misfires on cylinders #4 and #7. What is odd, both cylinders wind up showing the exact same misfire counts at the same time. When detecting the misfires, the SES light flashes. Anyway, as far as I can tell, the engine doesn't hesitate or make any strange noises. I'm wandering if my crank sensor is on the fritz (Note, I haven't dialed in the VE mapping since my engine build) Can anyone shed some light on this situation?? Thanks in advance!!??
09-08-2012, 05:10 AM
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Staging Lane
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Thanks for the reply!. I used a GM performance stock Z06 cam with the rebuild. I'm sure it has been explained, and please forgive me, but it would help if I knew exactly how the PCM determined that a cylinder misfires. From my understanding, it looks for an RPM drop for no particular reason, determines where the motor is in the firing order (#1, #2, etc), then keeps track of the number of times it records a 'misfire'?? Is this correct? Can someone ellaborate a bit more? Thanks again!
09-08-2012, 10:24 AM
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Staging Lane
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Wow Kurt, I didn't think of that!! Although, I just reviewed my firing order and noticed they are furthest apart. I didn't take it a step further to note that the crank sensor would be looking at the same position relative to the crank for #4 and #7. I appreciate you pointing that out. I'm gonna check my local parts people and see if they have a crank sensor. Does the PCM look at the crank sensor for RPM or the camshaft sensor?? Thanks!
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09-08-2012, 07:38 PM
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Just got my rebuilt LS1 back in my car and so far it is running GREAT! Motor has good response and a tail load of getty-up. Anyway, while logging data with my HP tuners, the scanner is picking up Misfires on cylinders #4 and #7. What is odd, both cylinders wind up showing the exact same misfire counts at the same time. When detecting the misfires, the SES light flashes. Anyway, as far as I can tell, the engine doesn't hesitate or make any strange noises. I'm wandering if my crank sensor is on the fritz (Note, I haven't dialed in the VE mapping since my engine build) Can anyone shed some light on this situation?? Thanks in advance!!??
Crankshaft Position Variation ReLearn
09-08-2012, 08:03 PM
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09-08-2012, 08:32 PM
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Crankshaft Position System Variation Learn
Important: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator, and the engine will respond to throttle position after the learn procedure is complete.
1. Install the scan tool.
2. Apply the parking brake.
3. Block the drive wheels.
4. Close the hood.
5. Place the transmission in Park if the vehicle has an automatic transmission, or in Neutral if the vehicle has a manual transmission.
6. Idle the engine until the engine coolant temperature reaches HC (150°F).
7. Turn OFF all of the accessories.
8. Apply the brakes for the duration of the procedure.
Important: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to additional diagnostic information.
9. Use the scan tool in order to enable the Crankshaft Position System Variation Learn Procedure.
10. Slowly raise the engine speed to 4,000 RPM.
11. Immediately release the throttle when the engine speed decreases.
12. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.
1. Install the scan tool.
2. Apply the parking brake.
3. Block the drive wheels.
4. Close the hood.
5. Place the transmission in Park if the vehicle has an automatic transmission, or in Neutral if the vehicle has a manual transmission.
6. Idle the engine until the engine coolant temperature reaches HC (150°F).
7. Turn OFF all of the accessories.
8. Apply the brakes for the duration of the procedure.
Important: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to additional diagnostic information.
9. Use the scan tool in order to enable the Crankshaft Position System Variation Learn Procedure.
10. Slowly raise the engine speed to 4,000 RPM.
11. Immediately release the throttle when the engine speed decreases.
12. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.
Sorry for the cut and paste atleast its from gm and not google.
09-08-2012, 09:03 PM
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Staging Lane
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Not sure how you do it with HP Tuners but this is how you do it with a scan tool.
Crankshaft Position System Variation Learn
Crankshaft Position System Variation Learn
Important: While the learn procedure is in progress, release the throttle immediately when the engine starts to decelerate. The engine control is returned to the operator, and the engine will respond to throttle position after the learn procedure is complete.
1. Install the scan tool.
2. Apply the parking brake.
3. Block the drive wheels.
4. Close the hood.
5. Place the transmission in Park if the vehicle has an automatic transmission, or in Neutral if the vehicle has a manual transmission.
6. Idle the engine until the engine coolant temperature reaches HC (150°F).
7. Turn OFF all of the accessories.
8. Apply the brakes for the duration of the procedure.
Important: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to additional diagnostic information.
9. Use the scan tool in order to enable the Crankshaft Position System Variation Learn Procedure.
10. Slowly raise the engine speed to 4,000 RPM.
11. Immediately release the throttle when the engine speed decreases.
12. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.
1. Install the scan tool.
2. Apply the parking brake.
3. Block the drive wheels.
4. Close the hood.
5. Place the transmission in Park if the vehicle has an automatic transmission, or in Neutral if the vehicle has a manual transmission.
6. Idle the engine until the engine coolant temperature reaches HC (150°F).
7. Turn OFF all of the accessories.
8. Apply the brakes for the duration of the procedure.
Important: If the CKP System Variation Learn Procedure cannot be completed successfully, refer to additional diagnostic information.
9. Use the scan tool in order to enable the Crankshaft Position System Variation Learn Procedure.
10. Slowly raise the engine speed to 4,000 RPM.
11. Immediately release the throttle when the engine speed decreases.
12. Turn OFF the ignition for 15 seconds after the learn procedure is completed successfully.
Sorry for the cut and paste atleast its from gm and not google.
