cij911

iTrader: (14)

Hey guys -- Can you help me understand why I might be getting an ocassional partial throttle knock? My car seems to be really 'sensitive' in the 4000 - 4500 area, but I can get 1 - 2 counts, even 3, at other RPMs with TPS < 40%.

Here are a few examples:

RPM, TPS, Timing, Wideband AF, Knock, LoadCalc
4718, 38.43, 17, 13.3, 3, 128.05

5468, 35.69, 24, 13.1, 2, 85.66

The reason this bothers me is that I like to drive the car hard, but very rarely have places for extended WOT runs, rather a lot of short bursts and feathering (country roads).

Thanks in advance!

EvoBroMA

the stock map did the same thing for me. Kind of surprising really. like you said its only occasional, so i'm not too worried about it.

C6C6CH3vo

iTrader: (9)

In 1st gear if throttle is less than half and rpm is less than 3000, I will always get knock. This is under vacume even before any positive boost.

I got so good at monitoring this with logworks that I can even move the throttle in such a way to make the knock #s rise or fall, makes me laugh.

Not concerned because pressures can't be dangerous at 250hz airflow and 90% load.

I think the knock sensor is too sensitive at low loads due to lack of noise so it picks up other things

cij911

iTrader: (14)

bump for any more advice...

jcsbanks

I don't worry about these part throttle knock sums if they are 3 or below. Never heard anything in the det cans or on the knocklink, less damage would be done anyway because the cylinder pressures are lower, and additionally, the way the knock control works it looks for changes in knock sensor output compared with the last value, which can alter with TPS and obviously boost building. So in the same way I certainly don't tune for 0 knock sums during spool up. As pointed out, stock cars do it.

Just make sure you're not too lean on part throttle if you run it for any length of time at decent boost levels.

C6C6CH3vo

iTrader: (9)

This is impossible in my case since the knock is being recorded at load levels during closed loop (70 - 90%) and the transition to open loop. (I've experimented with this here case discovering the the knock is independent of timing or A:F)

Once in open loop, or at WOT, the counts soon disappear.

I just want to make sure this is not preignition which, unlike detonation, can blow up a cylinder at low load levels (like less than 4psi boost)

jcsbanks

I mentioned decent boost levels because this is where the damage will occur, so I'm talking open loop. Closed loop trivial knock sums don't bother me at all.

To get preignition I think you'd need to have a fault of some sort or bad full boost tuning that overheated say a carbon ember/spark plug tip/exhaust valve etc.

The lean spool at 3500 RPM on the JDM IX did overheat some exhaust valves I believe when they were run on boost below 3500 RPM. I expect this could cause pre-ignition, but with a factory turbo car with no faults (ie not an aftermarket super/turbocharged engine with no intercooling, high compression and too hot spark plugs etc) I think pre-ignition should only occur with gross tuning errors?

klatinn

Hi,

Just FYI:
Preignition is "silent" and therefore cannot be picked up by a knock sensor. It can lead to detonation, but rarely.

Regards,
Klaus

coolguycooz

Somebody might as well throw out the exact difference between preignition and detonation?

cij911

iTrader: (14)

Well I am now more confused than when I asked the question ....

klatinn

This article might help, it describes it better than I could in a post.

http://www.streetrodstuff.com/Articl...ne/Detonation/

It has some minor mistakes though. The one I notices is that they say LPP occurs at 14 ATDC for any engine. That is not true. It depends on the engines bore/stroke and rod length stroke ratio and therefore occurs between about 13 and 20 ATDC depending on those ratios. For example big bore aircraft engines have LPP at 20 ATDC.

Regards,
Klaus

kmcconn9

iTrader: (33)

interesting, I just recorded 1-2 count of knock on spool up today. But once full boost hit, no more knock...Maybe more fuel down low for load...

wrcwannabe

iTrader: (1)

Chris .

I now get about 3-4 lines of 1-2 KS happening 2.5K -3.5 K on the tune we were talking about this monday tuesday...In fact sometimes this happens on closed throttle as revs decrease. Ive seen this even at 17-20 psi stock turbo/WGA.

At closed thottle it goes dead lean ,so maybe that is why, but light throttle at 80-100% load and low boost you would not expect it. But it is reproducible in my logs.

As noted by others above, I dont think it is dangerous. As john said stock cars do it so if Mitsu tolerates it then....

milburn

PS get your MX's yet?

Max Power

iTrader: (1)

This tends to happen with me as well... I got a freak 10 KC today on the track when doing part throttle driving (about 30% Tps, quick lift, back to 40% and bam - 1 line of 10 kc with 0 before and after). At this situation, I get a bit of bucking in the car too.

cij911

iTrader: (14)

Milburn -- Thanks for the note...I think some of the partial throttle knock is caused by transitions to/from adjacent cells (guess looking at my map). I hate seeing knock, so I will play with the map in the common transition, partial throttle spots.

I don't have the tires yet...I cannot believe I am having such a hard time deciding between a 235/45/17 Kumho MX and a 245/45/17 Falken 615....I think I should just go with the MX because of the size / weight and the fact that it is a street car. If I ever take it to a course (road course), I will put on race rubber.