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I wondered if anyone could help me interpret the following two DME reports. I'm concerned because the over rev appears to have been quite recent.
I'm not sure how serious it is?
I'm not a total expert in this, so someone can correct me if I'm wrong, but having seen a few CGT DMEs this is how I interpret it:
- Engine has seen over 692 hours of total operation. This is quite a lot - I'm guessing around 20,000 miles on this car?
- The car has over 35,000 ignitions at the lower RPM range. This basically means it has hit the rev limiter (and possibly gone slightly over the rev-limit) quite extensively throughout its life. The last time it hit this range was about 1 hour ago.
- The car has 1,250 ignitions at the "Range 2" higher RPM range. This is the "danger zone," and while the CGT engine can handle revs that will "trip" Range 2, the more ignitions in this area, the more you have to worry. I believe 1,250 ignitions would add up to multiple seconds spent in this range over the life of the engine, but I will let an expert calculate ignitions -> engine revolutions -> number of seconds for this V10. The last Range 2 overrev occurred on this engine around 5 hours ago.
- Both reports (DME Master & DME Slave) are basically showing the same information, you can look at one or the other.
Range 1 is from 8400 RPM (redline) - 9000 RPM
Range 2 Anything about 9000 RPM
If the engine has been over spun far past these two ranges a hard fault will be stored in the DME for diagnostic purposes and can not be cleared. That fault is P0219 - Engine Overspeed Condition
Range 1 is from 8400 RPM (redline) - 9000 RPM
Range 2 Anything about 9000 RPM
If the engine has been over spun far past these two ranges a hard fault will be stored in the DME for diagnostic purposes and can not be cleared. That fault is P0219 - Engine Overspeed Condition
Hope this information is helpful
Jimmy - you are in a unique position of having wrenched a really high number of CGTs. What do you see as "typical" for the cars that come through your shop?
A four stroke V-10 actually has 5 ignition events per revolution.
Lower range (8,400-9,000 rpm): 35,249 Ignition events /5 = 7,050 Revolutions. Divide by 9,000 RPM = 0.7833 minutes. Multiply by 60 = 47 seconds in that rev-range. Last Range 1 over rev 1.1 engine hours ago, approximately 33 miles ago
Upper range (> 9,000 rpm): 1,236 Ignition events /5 = 247 Revolutions. Divide by 9,000 RPM = 0.0275 minutes. Multiply by 60 = 1.6 seconds in that rev-range. Last Range 2 over rev 5.1 hours ago, approximately 153 miles ago
It is unfortunate that this early version of the DME report in the CGT only has these two ranges. Consequently, we don't know if the over-rev was a 13,000 rpm mechanical over rev from an erroneous downshift that should have been an upshift, or simply a 9,100 rpm throttle blip to show off the engine sound that got a little over exuberant. Later DME reports in 997 models, for example, have 6 ranges which help discern this better. A bad mechanical over-rev from a missed shift can end an engines life very quickly. If the engine is running well 5 operating hours after the upper range over-rev, it's unlikely any serious damage has occurred. IMO a total of 1.6 seconds of range 2 on a 20,000 mile car, with the last event over 5 hours ago is not a deal breaker, but perhaps an additional bargaining chip on an already high mileage car.
A four stroke V-10 actually has 5 ignition events per revolution.
Lower range (8,400-9,000 rpm): 35,249 Ignition events /5 = 7,050 Revolutions. Divide by 9,000 RPM = 0.7833 minutes. Multiply by 60 = 47 seconds in that rev-range. Last Range 1 over rev 1.1 engine hours ago, approximately 33 miles ago
Upper range (> 9,000 rpm): 1,236 Ignition events /5 = 247 Revolutions. Divide by 9,000 RPM = 0.0275 minutes. Multiply by 60 = 1.6 seconds in that rev-range. Last Range 2 over rev 5.1 hours ago, approximately 153 miles ago
It is unfortunate that this early version of the DME report in the CGT only has these two ranges. Consequently, we don't know if the over-rev was a 13,000 rpm mechanical over rev from an erroneous downshift that should have been an upshift, or simply a 9,100 rpm throttle blip to show off the engine sound that got a little over exuberant. Later DME reports in 997 models, for example, have 6 ranges which help discern this better. A bad mechanical over-rev from a missed shift can end an engines life very quickly. If the engine is running well 5 operating hours after the upper range over-rev, it's unlikely any serious damage has occurred. IMO a total of 1.6 seconds of range 2 on a 20,000 mile car, with the last event over 5 hours ago is not a deal breaker, but perhaps an additional bargaining chip on an already high mileage car.
A four stroke V-10 actually has 5 ignition events per revolution.
Lower range (8,400-9,000 rpm): 35,249 Ignition events /5 = 7,050 Revolutions. Divide by 9,000 RPM = 0.7833 minutes. Multiply by 60 = 47 seconds in that rev-range. Last Range 1 over rev 1.1 engine hours ago, approximately 33 miles ago
Upper range (> 9,000 rpm): 1,236 Ignition events /5 = 247 Revolutions. Divide by 9,000 RPM = 0.0275 minutes. Multiply by 60 = 1.6 seconds in that rev-range. Last Range 2 over rev 5.1 hours ago, approximately 153 miles ago
It is unfortunate that this early version of the DME report in the CGT only has these two ranges. Consequently, we don't know if the over-rev was a 13,000 rpm mechanical over rev from an erroneous downshift that should have been an upshift, or simply a 9,100 rpm throttle blip to show off the engine sound that got a little over exuberant. Later DME reports in 997 models, for example, have 6 ranges which help discern this better. A bad mechanical over-rev from a missed shift can end an engines life very quickly. If the engine is running well 5 operating hours after the upper range over-rev, it's unlikely any serious damage has occurred. IMO a total of 1.6 seconds of range 2 on a 20,000 mile car, with the last event over 5 hours ago is not a deal breaker, but perhaps an additional bargaining chip on an already high mileage car.
I thought the rev limiter cut in at 8,400 revs? If that is the case how can an over-rev be as a result of a "blip" to show off the engine?
As far as I can tell it can only be the result of selecting the wrong gear, causing the engine to over-rev.
I'm also not convinced that 5 hours of running is sufficient to determine that no serious damage has occurred. I'd feel more comfortable if it was 50 hours ago!
10-24-2018, 12:52 PM
Over rev report CGT
