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Thread: Spark for Decel - LNF?

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    Senior Tuner metroplex's Avatar
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    Spark for Decel - LNF?

    I have a 09 Cobalt SS/TC with the LNF and have been looking around the HP Tuners calibration file trying to find something resembling "Spark For Decel" that is found on Ford V8s with SCT Advantage.

    I'm trying to retard the spark with closed throttle/decel to see if it will keep the exhaust gases flowing and not cause as much turbo lag during decel... and also to see if it will make the exhaust pop more. I found out about this on my Mustang GT and it sounds like the new Jaguar F-Type when decelerating!

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    although im a noob at this, i'll take a stab at it, if im wrong the more experienced guys will correct me.

    first of all this is a bosch controller, bosch software, so there are a lot less tables unlocked compared to a more conventional GM software.

    if you are above something like 2200 rpm if you get off the throttle the engine will go into Decel Fuel Cut Off (DFCO), which (selfexplenatory) cuts off fuel completely. So before we talk spark, you'll need fuel first. To turn off DFCO, go to Engine>Torgue Management>General > ETC Limits, table Torque Mgt Cylinder Disable, 4x4 table,fourth column is all "15" turn those all to 0, and that will disable DFCO.

    as far as spark, i am not aware of a specific "decel spark" table, but you may be able to do something by manipulating "optimum spark" tables, maybe, but im guessing we dont have access to an actual table that does what you want. From what i noticed when you're off the throttle, spark goes to -3 deg, that is plenty retarded it seems like to me.

    All that said, i kinda question your reasoning. With a stock turbo, the LNF has virtually no lag, most people limit boost at low RPM to avoid the stock clutch from slipping, boost comes in early and hard if you tune it that way, stronger than the stock clutch can take. If you have a bigger turbo, that's a different story i suppose. As far as the "popping" to each their own, you can make it pop more with the above table i mentioned, but on this forum most people are about the "go" and don't really care for the "show". hopefully you'll understand what i mean by that.

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    Decel ranges in the spark tables are the top right corner cells. That is the high RPM low load tables. I have not done much with that section of the table, as I find it not to be very useful.

    The DFCO table that Turbo is talking about will give you the popping, but will also sacrifice fuel economy, if that has any bearing on your decision.

    Good luck!

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    Senior Tuner metroplex's Avatar
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    Quote Originally Posted by mkriebs View Post
    Decel ranges in the spark tables are the top right corner cells. That is the high RPM low load tables. I have not done much with that section of the table, as I find it not to be very useful.

    The DFCO table that Turbo is talking about will give you the popping, but will also sacrifice fuel economy, if that has any bearing on your decision.

    Good luck!
    I'll take a look at the spark tables, I think it makes sense for the low load / high RPM sections to do the same thing as the "Spark for Decel" function in SCT's Advantage. I've read that advancing the spark during decel would increase engine breaking, while retarding it will reduce this effect and allow more unburnt fuel to leave the exhaust.

    For my Mustang GT, I kept the stock Coasting Fuel Shutoff (same as the DFCO) for better fuel economy, but the rapid fire pops during decel are still present after I retarded the Spark for Decel values.

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    Correct retarding spark in low load/high rpm area of the ignition tables, will create more popping through the exhaust cause of having ignition when the exhaust valve is open.

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    Senior Tuner metroplex's Avatar
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    The only spark tables I see for the LNF is in Engine -> Spark -> Main Spark Advance and the 4 tables for the different valve settings.

    I'm thinking that the 15% and 20% load columns for 1500-6000+ RPM should be reduced to achieve the intended result?

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    No, you do not want to reduce in the 15%-20% load columns. You would want to lower the values in top right of the table. For example in 400rpm row reduce the 80%-200% load and, at 600rpms row reduce 100%-200% load and, at 1000rpms row reduce 120%-200%. And continue a pattern like that.

    The 15%-20% load columns for 1500-6000rpms are going to be used in cruising areas and normal operate areas of driving and need the positive timing there.

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    Senior Tuner metroplex's Avatar
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    Quote Originally Posted by Mark@TuckerPerformance View Post
    No, you do not want to reduce in the 15%-20% load columns. You would want to lower the values in top right of the table. For example in 400rpm row reduce the 80%-200% load and, at 600rpms row reduce 100%-200% load and, at 1000rpms row reduce 120%-200%. And continue a pattern like that.

    The 15%-20% load columns for 1500-6000rpms are going to be used in cruising areas and normal operate areas of driving and need the positive timing there.
    When I cut the throttle, the load generally drops down to the 10%-20% range and as soon as I open the throttle, the load increases above 20%. This seems to be the case on my Ford mod V8. I datalogged it and found if I cut the throttle at say 5000 RPM, the load drops down and stays down at around 15% even when I let it cruise/decelerate. If I reduce the spark values in the top right, that's low RPM and high load which I think comes from lugging the engine. Is the LNF that completely different?

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    Senior Tuner metroplex's Avatar
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    I pulled some older datalogs for my SS/TC and looking at the spark readings, the 15% load column is almost all single digit numbers. The 20% column is a bit higher, but I don't think I can retard the timing any more. My Mustang starts to pop nicely at spark values higher than the SS/TC. I wonder if the SS/TC exhaust is just muffled by the stock cats?

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    Do you have stock exhaust system on it? If so, that is most possibly why. But I have had a couple of LNF's with High Flow CATS that would pop really good. But I honestly don't think I have done one with true stock cats.

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    Shoot, I apologize but I just realized that I had said the top right when it would be the bottom left. I was going off of my memory and that's not always reliable lol.

    So yes, decel spark cells would be the bottom left portion. You can find what cells are active during decel by setting up a histogram and watching what cells it highlights. The 15-20% load columns would actually probably be for decel.

    However, look at a long log and see if when you decel the ECU compensates for 0 TPS, low load, and higher RPM condition by cutting ignition advance automatically. This SHOULD be a part of the DFCO condition.

    For instance, this is a snap of my ignition advance histogram during a 55min log. This is the average ignition advance.



    Note in the far left column that the average is substantially lower than normal which is also significantly lower than the commanded timing advance. This indicates that the ECU is controlling the timing for some table that we're not able to access, or potentially the DFCO table we're able to access but no one has really tried manipulating extensively.

    So, I think it would be wise to look into other means of manipulating the decel values, which may include a table we're not able to access through HPT, I am not sure.