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Thread: Pros/Cons of PE

  1. #1
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    Pros/Cons of PE

    I'm still having a hard time deciding how to setup my PE parameters on my 2012 Impala (3.6L LFX). I guess I'm not quire clear on the pros & cons of PE mode. In stock form, PE mode is not enabled until 95% torque and 90% pedal (until 5120rpm, where it starts enbling a little earlier @ 83% pedal and slightly lower from there on).

    I guess I'm just looking for a little input as to when and why I'd want to enable PE. Being that the stock tune doesn't enable it until 90% pedal for the most part, is there any reason/advantage to enabling it earlier? Any disadvantages?

    I know that PE mode "richens" the fuel mixture, but again, not quite sure how to decide when to have it enabled.

    Thoughts/opinions?

    Thank you!

  2. #2
    Tuning Addict 5FDP's Avatar
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    You'd lower the enable torque if you messed with torque management, like remove some TM. Doing 10-15% less would be fine.

    And otherwise you can choose how soon you want it to come on. There is also a MAP kpa value that must be met aswell in most cases. Maybe you'd want it at 60% throttle but have the map kpa at 85-90 and the rpm delay of 2,500.

    I personally like the throttle % at around 50-60% with the rpm delay of 1800-2000 and the map kpa of 80-90. That way when I roll into, The last "trigger" I'm waiting on is my foot. The rpm will already be above 2,000 and my map near or above 90 by the time my foot passes the 60% throttle mark.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
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    Thanks - I really appreciat the input. I am wondering though - what is the benefit of enter PE mode? Does it make the car accelerate faster? Keep the cats cooler? Any other benefits? And are there any "cons" of entering PE besides increased fuel usage?

    I guess I'm just trying to understand when and why you'd want to be in PE - and if there are any downsides besides using more fuel.

    Thanks again - I appreciate the input!

  4. #4
    Tuning Addict 5FDP's Avatar
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    Performance enrichment is there so the motor doesnt blow up.

    Most cars try to stay around 14.1-14.7 afr while just crusing around because thats the best place for fuel mileage and overall operation of the motor.

    You need more fuel when you have more air entering the motor is a super simple way to put it. If you had a fuel ratio really high like 13-14 afr while you are deep into the throttle with a high load situation, you'd be making tons of heat inside the cylinders and you'd see some knock aswell. It could lead to a chipped/broken/melted piston.

    There is no cons really because without it, you'd blow the thing up. Yes it uses more fuel when you are mashing the gas all the time, but that's a given. To answer the other question, more fuel is more power to a point, then it can lose power with too much fuel. Yes it keeps the cats semi cooler in a way, but it's not like you are going full throttle all the time.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

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    Thanks again - all very helpful. The main reason that I was "questioning" the need for PE and when to use it was becuase my stock tune doesn't use it unless I'm over 90% pedal - which is almost never... Does direct-injection make any difference? My car has an LFX (3.6L direct-injected) - just trying to understand why GM would only enable it under such minimal situations (90%+ pedal) if it's so important - and if I really should "invoke" it much earlier than that...

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    Just as a follow-up to this. I noticed that my tune has "Pston Protection" enable/disable RPM settings. Based on the above discussion, I'm assuming that this function is there to protect the pistons from lean conditions? By default, it's set to an enable RPM of 3800 and a disable RPM of 3600. I'm assuming that these settings will automatically richen the fuel mixture above 3800 RPM under certain conditions to avoid causing piston damage? Although, I'm not entirely sure what condtions are needed to enable piston protection (besides RPM) - becuase even when I'm above 3800 RPM, I don't see the commanded AFR being any richer....

    Anyone have any idea when these piston protection settings are actually used?

    I appreciate the assistance - I know a lot of this is very "basic" to many, but I've very "green" when it comes to understanding fuel ratios!

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    Bump - does anyone have any thoughts on why my stock 3.6L LFX engine (direct-injected) tune doesn't enter PE until over 90% throttle and 95% torque? Is PE tuned differently with direct-injection motors? Does direct-injection change the "rules" at all for AFR under heavy load? Just trying to understand why they would avoid PE at all times except until true WOT situations - especially if it's dangerous for the motor. I can understand reducing PE mode for gas milage, but not at the expense of risking damage to the pistons! :-)

    Also, I noticed that while in COT, the transmission is very hesitant to upshift at high speeds. Does the car act differenty while in COT mode in order to try and keep revs high while the AFR is so rich (to help cool the cats?)? It almost seems like it wouldn't shift from 4th->5th until after I was out of COT...

    Just trying to understand how this all works! Stock tune also uses PE Delay under all conditions. Any reason to disable PE delay?

    Thanks for any info anyone can offer!

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    After doing some further logging, it seems that I get more KR when using PE mode comared to when not using it... At this point, I'm going to lower PE values slightly, but keep them closer to stock, since lowering them so that PE comes on at like 60% throttle just seems to cause more KR that putting PE to like 85% throttle (much closer to stock). I'm assuming that direct-injection is just different and the "old" rules don't apply to direct-injection when it comes to PE. Someone please jump in if that sounds completely wrong! :-)

  9. #9
    Tuner cp-the-nerd's Avatar
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    Power Enrichment just bumps up fuel delivery when you're calling for power. There's no downside to making PE more aggressive except that you're using more gas sooner in the throttle. I have my PE set so it switches over as soon as I go beyond 50% throttle.

    The factory setting of 90% throttle and 95% torque is totally unnecessary. That's literally GM trying to eek out .1 more mpg at the cost of better driveability. If you're getting more KR, then something else in the tune needs to get dialed in a bit for best results.
    2017 Chevy SS 6.2L/6M

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    I understand what PE does in general (richens the fuel mixture), but I guess I'm just not seeing any advantage of bringing PE on earlier - at least in my car - in fact, I see disadvantages in that I see more KR and use more fuel.

    I've checked a few stock 3..6L LFX direct-injected engine tunes and all of them seem to have PE set up just like my 2012 Impala - 95% torque and 90% throttle.

    So I guess my question is if PE should be tuned any differently on direct injected engines. Becuase every LFX tune I look at seems to only bring PE on at VERY high torque/pedal thresholds - even the Camaros with the 3.6L LFX.

    Like I said, the car doesn't seem to have any more "get up and go" when I bring PE on earlier. So if it's just using more gas and causing more KR at WOT, then why bother? Obviously, it must be "safe" since it comes tuned that way from the factory... It alsmost seems like it caused "over-fueling" on these engines (which may be why I see more KR)...
    Last edited by jtrosky; 01-13-2016 at 03:26 PM.

  11. #11
    Tuner cp-the-nerd's Avatar
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    You're assuming it has to do with DI, but all the port injected 3.6L tunes I've seen are the same way you described, including mine. Based on everything else I've learned about the factory tune, it's either for fuel economy or an arbitrary decision someone made during development. If PE alone brings on too much KR, that's simply another factory mistake that needs to be addressed.
    2017 Chevy SS 6.2L/6M

  12. #12
    Tuner cp-the-nerd's Avatar
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    What I'm trying to say is, if you're operating under the assumption that everything GM did was for an important reason after thousands of hours of research and development, that's just not the case.

    My car's stock transmission table was absolutely horrendous. The 6-speed may have been new technology, but this thing was tuned like they'd never done any transmission programming in their life.
    2017 Chevy SS 6.2L/6M

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    When I look at the stock 2009 Malibu tune, I see PE being broght on MUCH earlier, by the way. I show it coming on from between 49% pedal to 69% pedal (it doesn't even have a "torque" value for PE like the direct-injected 3.6L). Your 3.6L non-direct-injected engine looks very different in terms of PE tuning, which again, makes me wonder if direct-injected engines are tuned differently for PE... I also noticed that piston protection is basicaly disabled on the LY7 tune, whereas it's enabled on the LFX tune, so maybe that is why PE is tuned differently - becuase piston protection will automatically add fuel to protect the pistons when needed instead of using PE for that function.

    Even 2016 trucks with the 3.6L LFX engine have the same PE values as every other 3.6L direct-injected engine I've seen. On the other hand, I checked the stock tune for my 2005 Buck LaCrosse (3.8L Series III) - and it appears to setup much like your Malibu for PE, which again points to something being differernt with direct-injection PE tuning. Or maybe it's just becuase of the newer ECMs and becuase they are tuned differently than the older ECMs in general.

    Unless someone can tell me that there is some siginificant advantage in bringing PE in earlier with this particular engine, I think I'm just going to put the PE values back to their stock values since I don't see any advantage when I lower them. Even if I didn't have any more KR that way (which I do), I just don't see the point since it doesn't seem to provide any benefits - at least not that I can feel.

    I'm also going to review some more tunes to see how PE is setup on other engines, incuding direct-injected and otherwise.

    If anyone else has any info on port-injection vs. direct-injection PE tuning, please chime in - even if it's just to say that direct-injected engines should be tuned just like port-injected engines when dealing with PE. Like I said, maybe the difference is just related to new-style vs. old-style PCM tuning differences and has nothing to do with the injection type - or the piston protection settings - or something else completely! :-)

    Just trying to understand it all and why these newer engines seemed to be tuned so differerntly in terms of PE...

    Thanks!

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    Quote Originally Posted by jtrosky View Post
    So if it's just using more gas and causing more KR at WOT, then why bother? Obviously, it must be "safe" since it comes tuned that way from the factory.
    I don't know much about direct injection, but like you said... it must be safe if it comes tuned from the factory that way, so if messing with the PE causes more KR then leave the factory setting.

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    Yeah, I guess if it's safe for stock tuning then I shouldn't worry about bringing PE in any earlier since I don't see any aparent benefit from it. I think most people bring it in earlier for safety sake if they've modified other portions of their tune heavily for performance. Since squeezing the most performance out of my daily-driver isn't that important to me (I'm tuning for driving comfort, not performance), I think I'll put PE back to stock and be done with it.

    I know that some people disable piston protection, raise COT temp thresholds, etc - I guess PE is much more important if doing things like that.

    Still kind of interested to know if PE should be tuned differently with direct-injection though if someone has any details! :-) Kind of curious now...

    I get the feeling that sometimes people tune things a certain way just becuase that's how they've always done it in the past - not that it's necessarily the right way to do it with more modern technology that may behave differently.

    "To PE or not to PE - that is the question"! :-)
    Last edited by jtrosky; 01-14-2016 at 02:25 PM.