Forum » General Tuning Discussion » Anyone able to tell me why i get knock on lift off on a standard jdm k20a?

Anyone able to tell me why i get knock on lift off on a standard jdm k20a?

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Hi everyone,

Ive been bugged about this for a while - and im not sure how to stop it - or if its even bad but i want some advice if its out there.

At times on the soft fuel cut rev limiter you'll get the haltech saying its picked up knock - or more than you would want it to when you back off the throttle totally while under full load - the car will knock.

not fake knock either - you can hear a really nasty ping over audio monitoring as well.

It will happen after a 100% lift off from the throttle.

Ive tried setting the zero load timing map to 0deg above 3000rpm, I've tried setting full vac parts of the map above 3000rpm to 0deg - and it still randomly just has a fit.

with datalogging at 100hz in the haltech and the knock monitor doing its own logging - it definitely happens when the throttle has backed off lots - or on a gear change on or near the limiter (again when you back off the throttle)

seeing its with "no load" - is it going to do much damage? its very clear on audio knock monitoring

OR

is the knock monitoring picking up some sort of pop n bang due to dumping all the timing and some sort of lean condition?

What can i log and monitor to try n figure this out?

Having said that - the factory ecu also did this as well on lots of gear changes when running at full load - so can i take a guess and say "it wont cause damage" if Honda are happy to have the factory ecu do the same?

I'm obviously kinda paranoid about it because rebuilding a jdm type r k20a is going to be annoying if it is going to cause issues down the track with these knock events

Cheers

Lawrence

Any chance the VTEC solenoid is deactivated at the same time?

Hey - thanks heaps for the idea David, but unfortunately no - it can happen before the fixed rpm (not windowed) vtec point - I also checked with cam angle as well - flat lined the cam angle table and still had it happening.

I even tried Andre's "force some knock to happen at low rpm/loads to hear what it sounds like" - it is definitely the same knock ping on lift off as forcing knock at low rpm does.

As the factory ecu did the same (and sometimes sounded even worse than the Haltech) I think I'll have to ignore it unless someone pipes up and is sure its doing harm as it should be under "no load" conditions.

Anyone with opinions and a reason for them - please feel free to chip in with them to add to the information pool :)

I see this in logs all to time that I get from different users, so it is pretty normal. Seems to be mechanical over-run related as I have never seen it on the dyno when I push in the clutch and lift off at the end of a ramp run, but often see on track cars I look after when they lift off at the end of a straight. So suspect it is more likely a mechanical noise, maybe clutch spline, pressure plate, gearbox or some other drivetrain backlash due to the torque reversal, or maybe even something really stupid I havent considered like the throttle blade hitting the stop hard.

Unlikely knock as cylinder pressure is very low under high speed over-run conditions.

Awesome - thanks heaps for that - more data points are always good - and from a Link person as well - schweeet - cheers for your input - its greatly appreciated thank you.