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One Cylinder Suffering From Knock while others are ok

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I am running an 09 Subaru WRX stage 2 with a Cobb accessport. While I am cruising down the highway the fuel system is in closed loop trying to achieve a target of lambda 1. However at certain loads the number 2 cylinder will start knocking. Only the number 2 cylinder is knocking (looking at the knock counter for each cylinder) all the other cylinders are good. It only suffers from knock at a given RPM Range and given injector pulse width range. It is running the stock injectors, so Cobb retained the stock map for injector pulse width trim per cylinder.

I am thinking that I will fatten up the curve in this area where I am suffering from knock for the specific injector for the number 2 cylinder. Has anyone else ran into an issue where they are receiving knock on a specific cylinder and they adjust the table for that injector? Or has anyone else encountered this scenario and has been able to solve the issue in a different way?



Hello just a thought but check a couple of things first swap that injector to the opposite side to see if the issue follows the injector compression test is also a good check on these engines to make sure its not the start of another issue

Regards Ross

Hey Ross Thanks for the reply.

The motor was just rebuilt because of rod knock on that specific cylinder. I bought the car from the mechanic that rebuilt the motor. He compression tested the engine and all cylinders were within a couple of PSI of each other. I was running the OTS map from Cobb and I know that those maps are very generic and not tuned for a specific engine. I also remember in one of the lessons Andre stated that sometimes even out of the factory a car will suffer from knock and the ecu will retard timing automatically. So I'm thinking that that one cylinder might just be prone to knocking and that might have been what took the bearing out in the first place? I also noticed that in the map location that the knock was occurring the AVCS was advancing the intake cam. So I just went ahead and retarded the timing for that area of the map by what ended up being about 5 degrees. It looks like it stopped the knock. I might do an extra degree or two that way I walk away from being on the edge of knocking. It is in a very light load area of the map but also an area that I would frequently pass through while cruising down the highway. So retarding the timing might decrease some power but the area of the map I am in, I am not requiring a lot of power.

I echo Ross's advice. An injector with a spray pattern issue, or clogged filter screen would explain single cylinder knock -- test for that. A hotter cylinder (often the last cylinder closest to the water exit) will also show knock signs first, so sometimes a bit more fuel for that cylinder is needed.