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Thread: Hitting Cylinder pressure limit

  1. #1
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    Hitting Cylinder pressure limit

    Hello, I'm working on a 2018 ford focus S with the 2.0 Duratec, the tune file is stock other then disabling some nannies like gear shift hang and tip in mgmt. the issue I'm currently having is that I'm hitting a cylinder pressure limit. Shortly after I'm WOT it will go from borderline spark source to cylinder pressure limit. Ive tried searching this issue in the forums but only come up with ecoboost stuff. The pcm also has a cylinder pressure limit table but it doesn't go into detail on what triggers it. Maybe i'm missing something??

    cyl pressure limit1.jpgcyl pressure limit.jpgCyl pressure limit 2.jpg
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  2. #2
    Cylinder Pressure limit table is the hard limit for maximum spark -- load vs rpm. Since you have modified your tip in it's not pulling enough timing and the hard limit table is stopping it(cyl pressure)

  3. #3
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    Be careful. That’s how u blow a motor

  4. #4
    I would go back and enable tip-in, and maybe change the tip-in airmass multiplier? Or you could enable tip-in and find out what mapped point you are in and add a few degrees timing to the borderline spark table for that rpm range?

    What is the reason you are messing with it? Bad throttle response?

  5. #5
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    Quote Originally Posted by Ranger Coyote View Post
    I would go back and enable tip-in, and maybe change the tip-in airmass multiplier? Or you could enable tip-in and find out what mapped point you are in and add a few degrees timing to the borderline spark table for that rpm range?

    What is the reason you are messing with it? Bad throttle response?
    My reason for changing tip is was to improve the initial throttle response. I?ve read turning off tip in management in the ECT section can Improve that. What?s interesting is that the cylinder pressure limit table has higher ignition timing then my borderline tables.

  6. #6
    The cylinder pressure limit should have the highest timing your car can take before it blows up. Your other tables should be lower

  7. #7
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    Quote Originally Posted by paulsmithsr View Post
    Be careful. That’s how u blow a motor
    I would like to be as careful as possible. But why would spark source go to borderline, cylinder pressure then back to borderline?

  8. #8
    You should be running around 30-50 degrees just driving and when you mash it should run like 16-20 but you need tip-in so when you mash it, it's not delivering 30 degree spark to a full load engine. That's why the limit was hit

  9. #9
    You have knock set to per cyl and you are logging global so getting null results... I bet if you log knock for each cylinder its through the roof when you mash it

  10. #10

    Look how i log

    Check this for ideas on doing your spark: Untitled.jpg

  11. #11
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    Quote Originally Posted by Ranger Coyote View Post
    You have knock set to per cyl and you are logging global so getting null results... I bet if you log knock for each cylinder its through the roof when you mash it
    Knock per cylinder is enabled from factory on this car, and I?ve tried logging every source for knock or spark retard and I do have each cylinder logging but no negative values

  12. #12
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    Quote Originally Posted by Ranger Coyote View Post
    You should be running around 30-50 degrees just driving and when you mash it should run like 16-20 but you need tip-in so when you mash it, it's not delivering 30 degree spark to a full load engine. That's why the limit was hit
    I?ll go ahead and re enable tip in and see if that changes, how would I go about increasing overall timing in my borderline tables if it will hit that limit? It would hit the same pressure limit on a totally stock calibration as well

  13. #13
    Some people use the pre-ignition or cyl pressure table as a global limiter instead of messing with all the mapped points, you just have one place to adjust. It can be done with cyl pressure too and it looks like that is the case with your tune. I compared the spark in cyl pressure table to optimum power and surprisingly cyl pressure is like 1 or 2 degrees lower than mapped point 8, 9, and optimum power in some places. So it for sure will be hitting that table. Mapped point 8, 9 and OP is what your car looks at for WOT spark from what I can tell.

    I missed at the bottom of your log there is cyl knock and I only see good values adding timing briefly when you stab it. So that's great news!

    It looks like it's hitting cyl pressure limit by design. Since you have only good knock you could try adding 1 degree at a time to 3500-6500rpm at .95-1.05 load range of the cyl pressure table and look for knock. I suspect 1 or 2 degrees will be plenty safe and most likely will get you off the table limit too.

    I have blown up engines so take my advice with caution.

  14. #14
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    Quote Originally Posted by Ranger Coyote View Post
    Some people use the pre-ignition or cyl pressure table as a global limiter instead of messing with all the mapped points, you just have one place to adjust. It can be done with cyl pressure too and it looks like that is the case with your tune. I compared the spark in cyl pressure table to optimum power and surprisingly cyl pressure is like 1 or 2 degrees lower than mapped point 8, 9, and optimum power in some places. So it for sure will be hitting that table. Mapped point 8, 9 and OP is what your car looks at for WOT spark from what I can tell.

    I missed at the bottom of your log there is cyl knock and I only see good values adding timing briefly when you stab it. So that's great news!

    It looks like it's hitting cyl pressure limit by design. Since you have only good knock you could try adding 1 degree at a time to 3500-6500rpm at .95-1.05 load range of the cyl pressure table and look for knock. I suspect 1 or 2 degrees will be plenty safe and most likely will get you off the table limit too.

    I have blown up engines so take my advice with caution.
    Wonderful, I?m glad that the knock values are not of big concern and the car is adding in timing, I?ll go back and re enable tip in just to be safe and like you said add a degree or two in the pressure table and see if helps, I guess it would make it simpler by just adjusting that one table to get final spark but I feel on this stock car isn?t necessary, maybe if it was turbocharged and that was the maximum allowed timing that would be almost like a failsafe correct?

  15. #15
    Correct, after all adders and multipliers and subtractors and everything all added, the cyl pressure table is the MAX it can command

  16. #16
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    Just add timing and go over cyl pressure limit And see how long it last. Lol
    Should run awesome till boom

  17. #17
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    Quote Originally Posted by paulsmithsr View Post
    Just add timing and go over cyl pressure limit And see how long it last. Lol
    Should run awesome till boom
    I would like to figure out why it?s hitting the limit even on a stock tune, the limit table actually commands more timing then any of the borderline tables. My goal isn?t to increase but get a hold on why it?s going in and out of the limit

  18. #18
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    Quote Originally Posted by Ranger Coyote View Post
    Correct, after all adders and multipliers and subtractors and everything all added, the cyl pressure table is the MAX it can command
    I?ve added some spark timing to my limit table and it still hits it, my question now is if any other spark timing table is higher then cylinder pressure at a certain rpm/load will it automatically go to the cylinder pressure limit table to keep everything in check?

  19. #19
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    Yea it the max limit so u don’t blow your motor u can hit it. Just don’t go over it