High number of misfires - Page 1 - Porsche General - PistonHeads UK

Looking for some advice on below that is shown on a check over of a Porsche. Is it something of nothing and showing a previous fault or something to be worried about / question. M120_Total number of misfires for all cylinders over the life of the control unit 15308

To be able to make an informed decision you/we need more context and information....... Model of the car? Miles on the car? Age of the car?

Pope said: To be able to make an informed decision you/we need more context and information....... Model of the car? Miles on the car? Age of the car? Cayman R 19,000 2012

Is it going up over time now or is it historical? If that is misfires from new you could rack up that many misfires on one limp home journey with a failed coil or a bad plug. On a wasted spark system it will detect 2 misfires on every revolution so if you are pottering home at 2000 rpm you would clock up 15000 misfires in 7 and a half minutes. Edited by OldGermanHeaps on Wednesday 15th December 20:23

OldGermanHeaps said: Is it going up over time now or is it historical? If that is misfires from new you could rack up that many misfires on one limp home journey with a failed coil or a bad plug. On a wasted spark system it will detect 2 misfires on every revolution so if you are pottering home at 2000 rpm you would clock up 18000 misfores in 9 minutes. Edited by OldGermanHeaps on Wednesday 15th December 20:22 It’s just the remark from the printout report, a one liner. Ok, that makes sense but my simple mind would have thought that any “repair” would have zeroed the misfires but think I may be missing something.

That might be one of the counters that cant be reset by normal means, like the eeprom flash counter or over rev counter.

OldGermanHeaps said: That might be one of the counters that cant be reset by normal means, like the eeprom flash counter or over rev counter. Thanks, seems I am over thinking, over rev is all good with only a couple in 2 and nothing 3,4,5,6.

As others have said; the misfires over the life of the CU is a bit of a non-event and nothing to worry about on that mileage / model year. It is a value primarily included for workshop diagnosis, it will give the committed tech the info needed to make an informed decision. Say the car has a faulty engine earth that when loaded causes sporadic misfires; knowing the history of the fault can add weight to an argument that additional parts or further investigation will be required - I have seen individual cylinder misfires values of 45000 ignitions on cars with 20k miles as an example. Of more interest to you, I would expect, would be the rough equation of mileage plausibility - mileage/run time (operating hours) which gives the average distance per hr that a car has done over its life: Example: 30000 miles/3000 hrs would translate as 10 miles per hour, the accepted norm for Porsche sales checks is 18-25 miles per hour, so in the example that car would have been a lightly used example but may have been a city car and spent a lot of time idling in traffic (or 'in a garage to keep its battery topped up') Example 2: 40000 miles/1000hrs would translate as 40 miles per hour - in this example the car may be a regular motorway user; and so on. We use the equation for plausibility in extreme cases: say a car is showing 10000 miles but has 4000hrs run time - this can have a few causes; it is potentially a mileage discrepancy (someone getting creative to boost a cars value?) which needs looking into and maybe there will be history to back the situation up/maybe not. PM over some more info or a VIN if you like

Pope said: As others have said; the misfires over the life of the CU is a bit of a non-event and nothing to worry about on that mileage / model year. It is a value primarily included for workshop diagnosis, it will give the committed tech the info needed to make an informed decision. Say the car has a faulty engine earth that when loaded causes sporadic misfires; knowing the history of the fault can add weight to an argument that additional parts or further investigation will be required - I have seen individual cylinder misfires values of 45000 ignitions on cars with 20k miles as an example. Of more interest to you, I would expect, would be the rough equation of mileage plausibility - mileage/run time (operating hours) which gives the average distance per hr that a car has done over its life: Example: 30000 miles/3000 hrs would translate as 10 miles per hour, the accepted norm for Porsche sales checks is 18-25 miles per hour, so in the example that car would have been a lightly used example but may have been a city car and spent a lot of time idling in traffic (or 'in a garage to keep its battery topped up') Example 2: 40000 miles/1000hrs would translate as 40 miles per hour - in this example the car may be a regular motorway user; and so on. We use the equation for plausibility in extreme cases: say a car is showing 10000 miles but has 4000hrs run time - this can have a few causes; it is potentially a mileage discrepancy (someone getting creative to boost a cars value?) which needs looking into and maybe there will be history to back the situation up/maybe not. PM over some more info or a VIN if you like PM sent, thanks.