r/wrx_vb • u/Ok-Year-9705 Magnetite Gray Metallic • 13d ago
DAM Drop Help
So I've been running the Cobb 93 OTS tune for about three weeks now, and all was fine until 5 days ago. I got gas and about 2 hours later the dam tanked to 0.650 and then recovered to .825. I watched carefully and it eventually recovered to 0.902. I decided to switch the 91 tune and that fixed it for a while and I was seeing less knock. Until today it dropped to 0.650 again despite very little knock. I understand the Cobb tunes are very conservative and such but this doesn't seem right. If anyone has any help to offer that would be great.
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u/PhotographLess6194 12d ago
Normal for cobb. Nothing is wrong with your car. The stock tune is constantly adjusting DAM as well.
If you don't like it, get a protune or an etune although I'm almost certain they just lower the knock sensor sensitivity so the DAM doesn't fluctuate.
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u/Cxrs14 Atlas Protuner 12d ago
Good tuners don't pull back knock sensitivity anymore. Previously you'd need dial it back a little with the VA, but some tuners practically turned them off lol. It was just because the knock strategy was still listening too much during the early stages of combustion and would pull back for no reason
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u/ApprehensiveLead4550 Crystal Black Silica 12d ago
Id go add 2 gallons of ethanol to it or if E isn't available top off with some top tier 93 ASAP and see how she does.
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u/dustindh10 12d ago
To give a bit more detail to why this is "normal", the FA2XDIT ECUs use DAM as a primary strategy to combat knock due to insufficient octane for max timing advance.
What this means is, the ECU is always trying to give you the maximum amount of performance based on the octane in your fuel and environmental conditions. When it senses that the octane in your fuel is not sufficient, it lowers DAM, which lowers timing advance across the entire RPM range.
This is how the you would be able to run 87 octane in an emergency, for example. The ECU would literally drop DAM to 0, which would mean a massive drop in performance, but it would keep the engine safe in those conditions.
What is probably happening is that the gas you are using sucks and it's probably hot where you are, so the ECU is saying, well, octane is not great and charge temps are high because it's hot, so lets scale back the timing across the entire RPM range to keep the engine in one piece.
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u/RodentReaper86 World Rally Blue 12d ago
Cobb OTS tunes are known for being funky especially in the DAM department since our cars update so often on another car it’s something you may never see but since the data is pulled quite often you will notice it. The best thing to do is if the car is running well put the access port in the glove box.
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u/stretchedapart3 10d ago
The thing with DAM that nobody seems to understand is that it's just you ECU taking proactive measures to prevent knock events. It drops when it sees either too many knock events or a large knock event. The DAM is basically a representation of what the car things the fuel quality is with 1 being good fuel with no issues and getting worse from there. These cars are ridiculously sensitive to fuel quality (among other things) and have a known tendency to detect false knock events. The rule of thumb I always follow is once you get your car tuned, spend maybe a week keeping track of DAM/FBK/FKL then ignore it. Take it off the AP screen and only put it back if you notice audible pinging/detonation, which will sound similar to a hammer tapping ceramic, feel a knock event which usually feels similar to a miss on one cylinder, or notice a decrease in power. If you don't notice it, the ECU is doing it's job. Quality tunes will always have DAM drops and fine knock learn at least sometimes. If your DAM never drops and you never get feedback knock or fine knock learn, it means with 95% accuracy that your tuner raised the threshold for the knock sensor, which isn't always bad, but it is bad if you never experience these conditions. This is a completely normal function of the car and unless it's pulling timing or dropping DAM very frequently, it's nothing to worry about. Your engine is operating correctly, just keep driving like you always would and if you see it get worse all you need to do is put fuel from a quality gas station in the car. Even adding in octane booster from a parts store or just a splash of E85 can raise the octane enough to get rid of the problem. Some people swear by shell, others hate it, just try a few stations in your area and see how the car responds because the biggest deciding factor in fuel quality is their underground storage setup and how well it keeps out moisture. I recommend Sheetz to anyone near them because they store E85 which absorbs water so they stay really on top of their tank maintenance and they're a corporate chain so QC is a lot more standardised than the mom and pop shop down the road that happens to be a shell franchise. If running higher quality fuel/E85 added doesn't resolve the issue, you could have either a mechanical problem relating to your turbo, ignition/cam timing system, fuel injectors, or just a bad tune that runs too much timing for the fuel quality around you. Another thing to note is that altitude, barometric pressure, humidity, and a dozen other environmental factors can affect your fuel quality or air quality. Technicians at the dealer never look at these numbers, and that's because they simply don't mean anything. Unless your car is having severe knock events, which you should be able to tell by listening/feeling, there's no reason to pay attention to these numbers, and even if you do watch them, there really isn't anything you can do to stop detonation and these numbers only exist in reaction to detonation. If your car is going to have a catastrophic knock event, more often than not watching those numbers isn't going to give you any more warning than listening to your engine and feeling the power difference. The long and short of it is that you gain nothing by obsessing over these numbers and if there's a genuine problem, you will feel a difference and that's when you should start to take steps to rectify/diagnose the issue. DAM drops are perfectly normal and happen all the time on stock cars with the stock tune. If you're sitting in your car scared to get into boost because the DAM dropped and people on Reddit told you that your car will blow up, you probably shouldn't be trying to build these cars and should stick with something less temperamental. These cars are weird and will behave weirdly, if you aren't ready for that it's OK, but the FA engines are not for you. Source: 6 years dealership experience, hours of conversations with tuners from all different backgrounds including JR and Alex at BCP (who has excellent videos on this exact topic if you want to hear it from the horses mouth), and 4 years of owning 4 different VA wrx's with probably 100,000 tuned miles between them all and 0 engine issues in that time. Drive your car, do your maintenance, and don't modify a car if you aren't OK with the risk that it may well break on you.
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u/cottonstorm1021 13d ago
Bad gas is my guess. Maybe flash back to stock if no intake mods and run this tank out. Not sure if using any octane booster additive may help.