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Thread: 18 392 False Knock and Tq Mng settings

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    18 392 False Knock and Tq Mng settings

    Hello, I've got a 18 392 with bolt ons. Stock file has knock retard with stock timing table. As I reduced timing in areas the ecm was seeing, just kept losing power and torque. By the time ecm was not reporting any knock, car was 13-15whp down from stock. So I'm assuming it is false. Timing is starting at 9* and ends at 12* through a pull. Thinking I might need to desensitize the knock sensors to get the timing right. Also, are you guys getting any benefits from reducing Tq Management on manual trans cars? If so what changes?

  2. #2
    Try leaning the fuel out to around 12.5 - 12.6 The 6.4L seems to be prone to fuel knock.

    If reduced timing eliminates the knock events, I would be extremely careful with desensitizing the knock sensors. The knock is likely real and the piston ring lands are extremely fragile.

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    Tuner in Training rockstar9528's Avatar
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    that is wat to low of timing to introduce knock, possibly false knock, of course when you lower the timing in those areas the car was making less power, if anything how is your fuel settings? leaning it out would make more prone to knock. as per the TM not so much on the manual cars but their is some stuff you can take out, also focus on the tip in scalar, set it all to 0s so cars not pulling timing during rapid throttle openings

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    I initially had the target lambda at .89. I also experimented with richening it to .82 lamda, and same ignition timing. Resulted with same knock and loss of power on the dyno with the richer air fuel mixture. I understand reducing timing would result in lower tq/hp. Sometimes if you can keep the ecm from pulling timing due to knock, can result in more power, depending on the severity of knock the ecm thinks it is seeing and the amount of retard being introduced. But even stock,with the ecm pulling timing and dealing with retard decay, the next "knock" event, decay, etc. It still makes more power.

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    Where are you getting your fuel??? I would check that first then if you still get knock check plugs, if they look good and\or change them. These motors do have very conservative knock thresholds so desensitizing isn't a bad thing. The only problem with this is that if it is real knock it will beat the rings out fast. You need to go through threw all the steps to make sure it isn't real and then and only then change the knock thresholds. If your fuel is good(pressure\quality\AFR), your plugs are good, IAT's are within reason and timing is good then you could desensitize the knock sensor until its gone. Also to note there are other factors that pull timing within the tune, so make sure its not pulling from somewhere else also. Goood Luck

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    But "knock retard" is going to be retard from the knock strategy correct? Or is there other table with timing retard that will pull timing that shows up under "knock retard"?

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    Your correct in your thinking. Just make sure you log timing to make sure it's not pulling from another table. Ex. Commanding 18* at 5500rpm but only getting 14* because of 2* of knock AND 2* being pulled from another table.

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    Also forgot about longterm knock strategy and decay time. Make sure it's not combing these two together. if your knock stays within the decay time it will add more knock retard to your knock strategy.

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    Has anybody had this dip in power at 4300-4400rpm? Almost every 392 Challenger I've had on the dyno has this dip. At the bottom of the log, I inputted a 0-5v analog out from the dyno for psuedo HP/Tq into the Mpvi2 so that you guys could see roughly what I'm talking about. The scaling is not perfect, I just did it so you guys would have a visual representation. Also, when I am going to Wot throttle it appears the throttle plate shuts down for a moment, but not during the 4300-4400rpm dip. P.s. this is with Knock Threshhold -25% in upper rpm's
    Attached Files Attached Files

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    Heres a screen shot if the psuedo hp/tq curve doesn't show up in your scanners
    Attached Images Attached Images

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    I'm gonna say that's where the manifold changes from a short runner to long runner. but I cannot see the page on my phone.

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    Theres a momentary "rich" dip also at the exact same sport that gradually comes back to target lambda. I looked at the Srv enable, and it is set at 4700rpm. Could be hysteresis, but being that the dip comes before the trigger point in the tune, maybe not. I'll move the activation point a bit and see if I can smooth it out. Is there a TqMan table that might cause the throttle position to momentarily close when I am entering Wot that is happening in the log? Thanks for your input, I appreciate it!

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    The only thing that comes to mind is that the pcm pulls timing on The shifts and depending on how much timing you have it could effect your Afr. Also there is a table on how fast the PE comes in when you go into PE. I know I had to adjust that in my tune with the whipple as it severely rich when I would got into PE. I'll send a snap shot of the table in a few

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    after looking at the tune and log nothing seems to stick out. Im curious tho if its related to COT ?? The numbers don't match up for it to be that but my tune is quite different than yours and all mine has this raised up about 100*. As for the dip going into WOT my best guess is it has to be in the TCM side of things and I have not dove down that path yet.. Id start with changing the srv tables and see what that does.. Keep us posted as im curious as well.

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    Set all your Base WOT timing tables to be the same as well as you WOT lockpin and vvt tables, This will take the timing variable out of the equation and see what happens with that.

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    Quote Originally Posted by FstdodgeKY View Post
    The only thing that comes to mind is that the pcm pulls timing on The shifts and depending on how much timing you have it could effect your Afr. Also there is a table on how fast the PE comes in when you go into PE. I know I had to adjust that in my tune with the whipple as it severely rich when I would got into PE. I'll send a snap shot of the table in a few
    I did some test runs on the dyno before I left, and it was the Srv Lo rpm enable. Weird thing was it was set at 4700rpm to exhibit the above dip. I set it to 5200rpm and it eliminated the dip. So thanks for that advice. It seems these cars are pretty sensitive to ambient temp. It is also difficult to get consistent ignition timing. I have decreased knock threshold sensitivity, and from run to run, it shows knock, then next run it doesn't, with same commanded timing in the table. Don't have these issues with Gm or Ford Ecm's. Haha. Last 16 392 with ProCharger was running 10degrees timing at 6lbs of boost with zero knock. So running 15-16 degrees Na should be alright, I'd assume. But knock sensors going off....sometimes..
    Last edited by h2.4; 09-03-2019 at 10:25 PM.

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    Raising the Srv fixed the dip in the Hp/Tq curve and the rich dip in air fuel also. I had been through the tune, and could not find anything related that could cause that, not knowing of the Srv until you suggested it. I was thinking it was something mechanical and not tune related. But couldn't find anything. Thanks again for that suggestion!!

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    Great to hear glad I could help

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    why does raising this even only to 4800 from the factory 4700 remove the dip like it does? Works great. Anyone know why?

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    Quote Originally Posted by LilSick View Post
    why does raising this even only to 4800 from the factory 4700 remove the dip like it does? Works great. Anyone know why?

    It's an air boundary deal, cut one of these SRV intakes open remove the valve and hardware and you don't get the dip at all, 1st time I saw it I thought it was due to the odd angle of the TB mount , then we tested a 6.4 SRT intake that some jeep hemi conversion guys was making , which put the TB in the middle(like the 6.1 or Edelbrock) and the dip was there also, cut that intake apart remove all the valving, glue it back together and ....Gone
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