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trav1s

False knock

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Posted (edited)

Evening fellas,

Got a BA XR6 turbo that I'm tuning, stock apart from cooler and intake. Doing a log on the spark PID and the Spark adder average for all cylinders, I find soon as it's on any kind of boost, it pulls timing out. I've made both BLK and the MBT both the same, adjusted the lambda correction table etc, I've got really conservative timing until I sort this out (4-6 degrees @ 10psi) so I know it's gotta be false knock. I've confirmed it's the knock retarding the timing as I 0'd out the knock scalars and it no longer pulled timing. Just wondering if anyone has come across something like this? Usually I would just turn the sensitivity of the knock sensor down until the false knock is gone but just curious if anyone has ran into this before.

Cheers,

Edited by trav1s

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Old engines and built engines with forged pistons that rattle at idle are notorious for it but that doesn't mean it isn't legitimate. You could have a blocked injector etc. Just to confirm if you take 7 degrees out of the entire spark map, does it go away?

If you stick a screwdriver on the block and rest your ear on it whilst its on the dyno, can you hear anything?

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Not to sure how old the motor is, AFRs ares solid. I've had it running basically 2-3 degrees (in the spark map) @ WOT 10psi and it'll pull timing into the negatives, don't have a dyno to test unfortunately, I just do road tunes.

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1 minute ago, trav1s said:

Not to sure how old the motor is, AFRs ares solid. I've had it running basically 2-3 degrees (in the spark map) @ WOT 10psi and it'll pull timing into the negatives, don't have a dyno to test unfortunately, I just do road tunes.

Pull 10 degrees out of the whole map and let me know if it still tries to pull timing. If only 1 injector is blocked your AFRs will look fine, you'll only pick it up via knock detection or individual cylinder EGTs.

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He does have bigger injectors to put in, so I’ll stress to do that sooner rather then later. In the mean time, I’ll attempt to pull 10 degrees out of the whole map and report back. Thanks for your help Roland. 

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Yeah obviously you would't send a car out like that, but it is a very quick test to determine if it really is knocking. Even if its running 13.5 AFRs it shouldn't knock if you retard timing that much.

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Yeah that's right, that's why I put 4-6 degrees on boost, because I know it's 100% not knocking on that timing with 11.8AFRs. I'll still attempt to pull the 10 degrees out of the rest of the map though.

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Just waiting to get some time with the car, he's been a bit busy so haven't had a chance to fiddle yet, will update as soon as I get a chance, hoping for tomorrow. Is yours a BA as well?

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I understand the importance of proper knock detection and is awesome using headphones (Adaptronic ECUs come standard with 3.5mm jack) but I've tuned plenty of powerFCs which solely use knock the sensor and can confirm they work a treat, same with the Link ECUs. Guess that's not the case with these here? figured they'd be better with the donut style knock sensor, if it's just a case of the knock sensor needs to be desensitized, that's an easy fix, it's usually what I do with the Link ECUs too, rule out background noise which I guess that's what I'm facing with this. Obviously headphones or aftermarket knock detection is the way to go, not denying that.

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So just curious, if you ran into this issue, you'd disable the knock sensor from pulling out timing, put your aftermarket detection gear, start ramping timing until safe. Would you then desensitize the knock sensor as now you know it isn't picking up any knock and be done? or leave it disabled?

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5 minutes ago, trav1s said:

So just curious, if you ran into this issue, you'd disable the knock sensor from pulling out timing, put your aftermarket detection gear, start ramping timing until safe. Would you then desensitize the knock sensor as now you know it isn't picking up any knock and be done? or leave it disabled?

If it is your car and you are happy risking the motor you can disable it. If it was a customers car you would be crazy as a fuel pump can fail, blockage in the fuel filter, injector blocked. Collapsed cat, all sorts of things that will make a motor knock badly.

On a street car you aren't going to notice 2-3 degrees being pulled occasionally due to false knock so I would leave it enabled.

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13 minutes ago, trav1s said:

I was asking how you would tackle the issue, if it came into your workshop as I'm curious.

We are software engineers not tuners, we have tuned our own cars/helped tune others and we also have an intimate knowledge of how the PCM works but we are not mechanics or tuners so we try not to give hard and fast advice as there are more experienced people out there. We don't have a dyno or workshop and run everything from an office in SA with 2 remote workers (Darryl is in VIC).

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