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Knock On Back Off/coasting - Pfc

Kwyjibo

By Kwyjibo,
in Engines & Forced Induction

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Kwyjibo Rising Star

Kwyjibo

Posted
Posted (edited)

Hey,

Have checked Paul's FAQ page and done a search but can't find anything on this.

I know the knock sensors are fairly dodgy but I'm noticing that I get spikes of up to '40' knock when I come off throttle on my PFC. I also get knock of around 20-30 when coasting with absolutely no throttle. As soon as I open the throttle this drops to below 15 right through the rev range.

Just wondering if this is normal? I have heard knocking at low revs/load isn't *as bad as at higher loads but I would have thought getting knock anywhere still means premature ignition and damage to pistons.

If this is the case where would I look at reducing timing? Just wherever the map tracer is sitting when coasting?

Cheers,

Adrian

Edited by Kwyjibo
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https://www.sau.com.au/forums/topic/284700-knock-on-back-offcoasting-pfc/
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skylinecouple Experienced

skylinecouple

Posted
Posted

Hey, would like to jump in here. How much have you added to your numbers ? I am at 46 in the LO1 and 2 at No7 throttle area and not getting more than 3-4 knock. How hi can this keep going before it knocks at say ten and like you said, every engine is different. Have posted in Paul's PFC thread but I guess there aren't too many people tuning their own cars.

Kwyjibo Rising Star

Kwyjibo

Posted
  • Author
Posted (edited)

Haven't actually adjusted it from standard yet. Pretty much just finished all my mods and I'm about to organise my tune. It defintely feels as if the timing is much more retarded than my original ECU as it is a lot less snappy. I did try doing the temp ignition correction for one small drive(+2 and then +4) and it brought it back to how it felt previously and knock levels stayed exactly the same. Of course don't know how this would affect medium to high load situations as I didn't want to risk it.

I think I'll just talk to my tuner to make sure its safe.

Edited by Kwyjibo
Kwyjibo Rising Star

Kwyjibo

Posted
  • Author
Posted (edited)

Nope. Just took it around the block a couple of times to make sure it was running ok after putting some stuff back together. I want to make sure everything is sorted and working properly before I spend money on a tune. Basically I just checked that its running safe AFR's for the drive to the tuner but then noticed this funny situation.

My impressions from the Power FC faq is that the standard maps are pretty similar to the standard ECU.

But seriously can someone tell me if I should be worrying that knock jumps up under absolutely no load but is fine off load? I would have thought premature ignition is bad at all times but I'm not very mechanically minded and the FAQ indicates otherwise.

Edited by Kwyjibo
JonnoHR31 Grand Master

JonnoHR31

Posted
Posted

it can be bad but no where near as bad as under full load. 20-30 under light load before a tune is nothing to worry about. myne was pinging its tits off on the base pfc map, just use the temporary adjustment until you get it tuned properly

~Nvied~ Rookie

~Nvied~

Posted
Posted

I reckon those knocks are fine. Anything over 60 should be concerning. I run a pfc as well and i get no knock at all through low rpm and i get knock of about 6-7 at 2500 to 2800 rpm for some odd reason. I also get some knocks off like crazy 100 or higher the odd few times hardly ever though.

Any my engine is still running like knew so i reckon after a tune ... you'll be all sweet. I wouldn't recommend driving it before tuning it properly though incase there is too much difference which may end up causing damage to your engine.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
Nope. Just took it around the block a couple of times to make sure it was running ok after putting some stuff back together. I want to make sure everything is sorted and working properly before I spend money on a tune. Basically I just checked that its running safe AFR's for the drive to the tuner but then noticed this funny situation.

My impressions from the Power FC faq is that the standard maps are pretty similar to the standard ECU.

But seriously can someone tell me if I should be worrying that knock jumps up under absolutely no load but is fine off load? I would have thought premature ignition is bad at all times but I'm not very mechanically minded and the FAQ indicates otherwise.

You have not tuned it - and you are asking about possibly wayward knock numbers...

Been a while since i've heard something like that.

Every car is different. Go and get a TUNE. Driving around on the stock map proves/achieves nothing.

The FAQ assumes you actually have gone and had the car tuned, it does not assume you are driving around on the stock map.

Kwyjibo Rising Star

Kwyjibo

Posted
  • Author
Posted

Sorry I guess my original question should have been 'do you think this will be safe to drive to the tuners'. I am wondering if it is usual for knock to go up when letting off the throttle. I know the numbers are going to be screwy before getting a tune but if I drive its 10km and I don't want to destroy my engine in the process.

PsYLoR Collaborator

PsYLoR

Posted
Posted

Yes it will be safe to drive it 10km to the tuner? - you should re read the Power FC FAQ again, then read it once more after you've read it twice already.

If your still worried, when you drive it there go to SETTINGS,,,, IGN/ INJ

Change the Ign Timing down -10 so the whole map is down 10 degrees everywhere - wont see much knock then.

Kwyjibo Rising Star

Kwyjibo

Posted
  • Author
Posted (edited)

Relax, no need to be like that. Above I posted I dropped it 2, and then 4 degrees retarded and exactly the same thing keeps happening, no change in knock. I'll just drive it there.

Still am interested to know if anybody has any theories as to what could cause this spike to happen in an engine when you back off, lets say after it HAS been tuned.

Sorry for the newbie questions but I am a Software developer, not a mechanic and I'm building this car up as a hobby so I have much to learn and the best way is too read and ask questions.

Edited by Kwyjibo
PsYLoR Collaborator

PsYLoR

Posted
Posted

It could be related to any number of things, it helps to be more specific with what you have done to the car if you want some help, but at the end of the day its all going to be speculation until you take it to be tuned professionally.

Seriously now.... It could be as simple as something taping from the change in inertia and making the knock sensor give a reading.

skylinecouple Experienced

skylinecouple

Posted
Posted

Once you have it tuned with the correct AFR's then you can go ahead and tune the timing for a best result. There is no way the tuner is going to put in hours of work to tune the ignition from idle to redline, he'll just make it safe from boost transition to the red.

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