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Old 03-28-2021, 09:31 PM   #1
Canucked
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Default Knock with FA20 cobb 91 tune

I ordered a ton of parts for my '20 wrx. The accessport happened to arrive first. So I got it set up and ran the 93 tune for probably an hour before noticing knocking. I kicked it down to the ver. 4 91 tune thinking my local gas was ****.

I've been running it for about a week to work the kinks out and let the ecu learn. But I keep running into knock in 4th gear while cruising. Climate control off and being gentle it runs -1.41 on the sensor and I can watch it zero out. I can't figure out why it's happening.

I know it's within specs to ignore it but I can't figure out why it keeps happening under mundane conditions. Is it just learning?
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Old 03-28-2021, 10:29 PM   #2
X49
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Knock tends to be just as likely at lower engine loads as it is at high engine loads. This is because a modern engine's ignition timing is tuned to be near the limit of knock at all loads (except very low loads). Any knock at loads below around 0.35 g/rev is almost certainly false knock.

Knock at low loads is not very damaging to the engine, so it can be safely ignored. I like to use Accesstuner to tune out most low load knock, but this is time consuming and typically professional tuners are only going to focus on tuning at wide open throttle. Either run better fuel with that map, ignore the knock readings, learn to tune it out with Accesstuner, or get some detailed logs of the loads/RPMs it is occuring and convince a tuner to address this knock in with an e-tune.
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Old 03-28-2021, 10:33 PM   #3
Canucked
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When my parts from Grimmspeed come in I have a protuner lined up to make it work. Should I just wait? I'm just confused as to why an OTS tune in ideal conditions (low altitude and temp) would cause problems.
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Old 03-28-2021, 10:57 PM   #4
X49
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Quote:
Originally Posted by Canucked View Post
When my parts from Grimmspeed come in I have a protuner lined up to make it work. Should I just wait? I'm just confused as to why an OTS tune in ideal conditions (low altitude and temp) would cause problems.

Altitude and temperature are adjusted for in the tune. At lower intake temperatures, more ignition timing is added to increase power and efficiency. If these tables are well-tuned, knock will be just as likely as low intake temperatures as it is at high intake temperatures. Again, the engine is tuned to be near the limits of knock most of the time, and it takes advantage of factors like low intake temperature, low coolant temperature, or high altitude to advance ignition timing and increase power and efficiency while staying close to the point of knock. It's a feature, not a bug. As long as your DAM is not going down, it's not something that most people would bother tuning out.
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Old 03-28-2021, 11:02 PM   #5
Canucked
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Quote:
Originally Posted by X49 View Post
Altitude and temperature are adjusted for in the tune. At lower intake temperatures, more ignition timing is added to increase power and efficiency. If these tables are well-tuned, knock will be just as likely as low intake temperatures as it is at high intake temperatures. Again, the engine is tuned to be near the limits of knock most of the time, and it takes advantage of factors like low intake temperature, low coolant temperature, or high altitude to advance ignition timing and increase power and efficiency while staying close to the point of knock. It's a feature, not a bug. As long as your DAM is not going down, it's not something that most people would bother tuning out.
DAM has not moved. So when people say +or- 8 for knock they really aren't kidding. The car is going oops, i went to far lemme bring that back a bit?
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Old 03-29-2021, 11:07 AM   #6
PyroguyFTW
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How many miles are on the car?

Is there anything loose in your engine bay? Sometimes aftermarket beauty covers work loose and set off the sensor. Along with that, is there a specific condition you notice it more often? Rpm range, load/boost range, etc?

Do you have any nearby stations that sell race fuel? If so, I would try running the tank as low as you can(don't go to empty, that can gunk up your fuel filter if you do it, and causes all kinds of issues) and fill up with ~2gal 100+ unleaded and see if it continues. If so, I would wonder if you have something else going on(bad plugs, etc).
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Old 03-29-2021, 01:52 PM   #7
tegxsi
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First of all, All engines will have knock.

These cars are pretty knock sensitive compared to the EJ. Small amounts of knock at low loads or part throttle are not a concern unless it repeatable and/or causes the DAM to drop significantly.

These ECUs don't have much to learn. There are fuel trims (AF Learn) and Fine Knock Learn. Knock is in -1.4 increments. The smallest insignificant amount of noise the knock sensor picks up will give you -1.41.
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