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Old 06-24-2018, 01:08 PM   #1
drivetrainwrx
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Default Lowest DAM I've seen yet

So I have to commute way farther than usual a few days a week for work. I decided to switch things up and go back to 91 OTS from my MAP 93 stage 1. I must've gotten one hell of a bad tank of gas. An hour into my drive, my DAM dropped to .312. I just decide to cruise, stay out of boost and after work I'll top off with 93 on my way home. So I fill up at Shell, and wouldn't you know it, my DAM continues to go crazy and went as low as .06. What I thought was weird, was I didn't get a lot of crazy knock, only 1 or 2 events up to 4.xx, and a couple of FKL of 5.xx. The majority of FKL and K was >2.8 but consistently kept showing up dropping my DAM. I cruised back home and it was the longest drive of my life. The slightest input of throttle at highway cruising speeds would trigger an event. I even switched back to Stage 0. 30 mins into driving home with stock mapping, and my DAM dropped again to .06. I kept filling up with 93 every 1/4 tank, and a reflash back to 91 OTS. It's basically stayed at 1.0 but I've still seen a few FKL events of 5.xx between 3-5k in 2nd and 3rd gear. With WOT, I didn't see any events but it scares me how fragile these motors are with just a bad tank of gas.

I figured I'd share just in case anybody else had a similar experience or was worried that their car was crapping the bed. From what I've seen before, most members worry over anything lower than 1.0. I do too to a certain point, but I'm not sure what else I can do about it. I'd get an etune/protune if I could, but it just isn't financially feasible ATM. Do I need to be worried about the long term impact a series of events like this can have on my motor? I heavily rely on my car for my commute, and have put 60k on since purchasing in 2016 with zero issues until I purchased my AP/MAP stage 1. Were these events likely happening prior to my purchase? I've only had my AP for a few months when weather started creeping consistently into the 70's/80's with high humidity. I also have to wear a shirt and tie, so there's no way I'm not using AC, but it also seems like AC significantly impacts my readings as well.

Sorry for the novel, but I'm really new to Subarus and any modifications whatsoever. Is a protune/e-tune my only option? Thanks for any feedback.
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Old 06-24-2018, 02:53 PM   #2
Perscitus
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Don't worry. A DAM (IAM) at 0 or near 0 means nothing without context of tune (timing tables, maf scaling, load comp, various temp comps af error, boost error, etc).

A DAM/IAM at 1 is also fairly meaningless and depending on tune, the difference between a 1 and 0 may mean nothing in terms of total timing too.

Read up in numerous threads on here, over at COBB, RomRaider, Ecutek, LegacyGT forum, etc. and the various tuner FAQ sites for FA20DITs.
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Old 06-24-2018, 03:08 PM   #3
drivetrainwrx
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Thanks, I appreciate it. Where can I find these threads? I've basically tried searching google, youtube, cobb and a few of the threads on here but wasn't able to find much. I probably just didn't look hard enough, although I'm still pretty new to the forums.
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Old 06-24-2018, 04:09 PM   #4
Perscitus
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Start here:

https://www.cobbtuning.com/subaru-knock-monitoring-and-dit-knock-logic-changes/

https://cobbtuning.atlassian.net/wiki/plugins/servlet/mobile?contentId=26870256#content/view/26870256

https://phatbottituning.com/2014%2F15-wrx-instructions

http://www.romraider.com/forum/topic1840.html

https://legacygt.com/forums/showthread.php/everything-you-wanted-know-subarus-knock-prevention-strategy-254139.html
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Old 06-24-2018, 09:51 PM   #5
drivetrainwrx
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Thanks!
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Old 06-25-2018, 02:00 PM   #6
Dazzo
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My dam dropped just like that when I paid in the store and told the guy 91 but the pump stayed with 87 octane and didn't switch correctly, I knew it as soon as I pulled out of the station.

FKL was dumping timing and Dam went to 0.312. I added some torco octane booster and and 91 Octane and watched the dam climb back to 1.00 over the next day of driving. I drove it like an old lady until I ran all two tanks through it.

I now have a protune and it put down great numbers so don't sweat it.

Last edited by Dazzo; 06-26-2018 at 12:28 PM.
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Old 06-25-2018, 04:06 PM   #7
Perscitus
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Things don't quite work like that, but yes the net effect is the same - no need to worry about this stuff unless under specific conditions:

a. in boost (say above 5psi)
b. at higher load (say above 1.3g/rev)
c. at higher RPM (say above 2K RPM)
d. at high static throttle plate % (or at WOT)

And even then, it might just indicate a meh tune (stock or otherwise), poor quality gas
and a nearly endless list of other things that can cause false knock signal.

The Subaru Denso/Hitachi ECU control logic is actually fairly archaic and primitive (by other mass-production manufacturer's standards as of 2018)... the engine design and sensor placement isn't helping either. If anything, the whole thing is plagued by over-reacting to poor signal inputs from low-fidelity and too few sensors (cost).

At least the stock strategy is to constantly try to add timing back to ride at the cutting/bleeding edge of the timing map limits. Whether that's good or bad depends on the tune.
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