False knock on 1.8 bbr turbo
 

I'm running a 1.8l engine, 320cc (soon to be 460cc) injectors, T25 turbo, adaptronic ecu.

I changed the ignition to closed loop and fuel map to rapid learn after changing to volumetric efficiency (VE) with my impending injector upgrade.

After switching from open loop to closed I started experiencing a huge flat spot between approx 4500rpm and 6000rpm and it would then pick up again at 6000rpm and pull normally to the redline.

I've read these engines are very noisy around this rpm band and want to know how to make sure its not real knock or detonation? And how do I work out the levels to let adaptronic know its not real knock and just surrounding noise.
I'd ideally like to run closed loop so the ecu can wind back the ignition if it experiences real knock.

Any thoughts guys?

Build/buy a set of det cans and listen for yourself. Bolt a crushed piece of 1/2" copper to the engine on the passenger side motor mount, attach a 1/2" nylon hose to it, and run the nylon hose into a set of construction earmuffs (drill a hole in the side). This will let you hear detonation clear as a bell - normal sounds are rhythmic, detonation sounds like some guy rattling marbles in a jar.

The AEM has a 2D map that allows you to set the voltage threshold for detonation to different values at different RPMs - this would allow you to "desensitize" it in the 4500-6000 range, while still maintaining usable values everywhere else. You could also get a sensor that's frequency filtered, or build a filtering circuit to do the same.

Search "knock tuning" or something like that. I know for sure that we had at least 1 or 2 detailed threads about EXACTLY what you're asking for.

Basically there's a table where you set up knock sensitivity. Basically tell the adap to ignore a pre-set amount of knock at a pre-set rpm.

Most people 1st would sweep the range at idle/without driving and if it picks up knock zero it out in the knock table.
Then VERY light/off boost driving. Also if you're decelerating and it picks up knock its most likely false knock as well.

Check it out, there's even a good base knock map posted you can use to start off with.

And yes, NB's pick up a ton of false knock in the 4500-5500 area. Or at least many of ours did when we all ran adaptronics



****Edit: Sav beat me to it. But yes, another great way to check if its real is with det cans. Super cheap and super effective

cheers for the replies guys.

I've just been reading up more about the adaptronic knock stuff.... Apparently the ecu has a 3.5mm jack so i can plug some headphones in and listen to the signal from the knock sensor.
is this going to be as reliable as detcans?

Oh yeah, forgot about the 440 having that feature. Should work great IMO. Awesome feature to sort of "double check" the stock sound filter, kudos to adaptronic for implementing it

Yea the new knock detection system is a great tool. I really hate tuning 420s now because of it. Its just easy when all you have to do is reach down and plug in. No mounting det cans or expensive hardware.

You're running a 420 though aren't you Tom? Unfortunately the 420 didn't come with a headphone jack.

After whipping off my kickplate I found that out :-(
Just waiting for a personal amplifier to arrive so I can rig up a permanent knock mic on the block and connect it to headphones in the car so I can find it out.

I tried the 20% fuel trim + timing of 10degrees BTC and logged a few runs through various rpm and loads and built up a bit of a 'false' knock profile and with those entered into the background knock level and running it in closed loop the flat spot has all but gone but i think there still needs to be a bit of fine tuning with either the ignition or the background knock level to get it perfect.

Tom, you could look at this for info on building det cans:-
http://www.mx5nutz.com/forum/index.php?showtopic=27620

There's probably a guide on here too, but I don't know where it is, soz. But the nutz one will be specific to where you can buy the stuff in the UK.