DaOne54

Hey CL!
So my Knock learn is pretty low, I've been trying to figure out why this is happening. I've done the basics, cleaned out my throttle body, Removed the oil that accumulated in the intake manifold, replaced air filter, made sure all of the plastic covers are properly secured. Spark plugs were also replaced 4k miles ago.
My Knock learn will drop fairly quick.. I've seen it as low as a 13 after a few trips from resetting the ecu... (which starts at 15 after its reset)
Ive owned the vehicle for about 6k miles. I performed injector fuel cleaner a few times in the past, about 2k miles ago.
I've always pumped shell 91 (highest octane available here)
I've been able to check the knock learn on another ISF locally, and it was at 19, so i feel like the fuel here (91) isn't the problem, and neither is the dry high temperatures.

I haven't tried Adding higher octane boosters YET.

I have a manifold crack, So I'm planning on going with PPE headers and RR racing tune... BUT before I spend all the money on that I'm trying to make sure that the headers will fix my low knock learn numbers. The other ISF I compered knock learn with also had a cracked manifold, But maybe it wasn't as bad of a crack as mine and wasn't causing the low numbers?



The way I've checked my knock learn numbers has been on idle, is that how everyone checks theirs?
I basically want to make sure that the PPE headers will fix my kock learn... before i fork out all the cash and figure out I need another more expensive part to actually improve my numbers.
VP Racing is the only gas pump that sells higher octane, 100 octane fuel. And its about $10 a gallon...

Any info on this would be greatly appreciated!
Thanks.

blackisF08

iTrader: (2)

mine does the same, i am pretty sure it is because the manifold cracked as well

Max16

Maybe the knock sensors can read the manifold leak as knocking....
Knocking is a precise frequency on each different engine. A leak can be misleading to that....

DaOne54

That's what I'm hoping for. I wasn't sure if other members had gone through this before or not.
Im hoping its the exhaust leak causing abnormal pulsation causing the knock sensor to rear something.
It just throws me off because the ISF i checked the knock learn on was also in need of new manifolds.. so I was getting mixed emotions about it being the problem.

Max16

In both cases, I wouldn't run cracked manifold for long. They can lead to false readings for O2 sensors also.
Either change them for stock or aftermarket.
Being in that area, I would change them for aftermarket for sure!

Defratos

Now how exactly do you have a cracked manifold and have that as being normal?

First time I hear about cracked manifolds being a common issue on the ISF, (maybe I've just missed this).


If you have a cracked manifold then get that fixed first, I wouldn't enjoy driving my car with a cracked manifold. Better yet get PPE Headers and just call it a day.



Now as for low KCLV I've been doing a bit of data logging over the past few months.

From what I know you should do a 3rd gear pull from 3k rpm to red line and record the data, not at idle.

Also try and load the car and do a few runs, from what other members have tried this helps with getting your KCLV numbers up.

Loading the car = Basically find a nice stretch of motorway, generally speaking you'll be in 3rd or 4th gear......Shift up to 6th gear and push your accelerator down to the end (you're not trying to get it to silly speeds, you're just loading the car) or ECU or something.

Try this in 6th, 7th gear even 8th for the hell of it and just see what happens to your KCLV numbers.

The last time I logged my car which is after my 60k service (3 days back) my KCLV is at 19.6.

The highest I've ever managed to get it to is 20.5 and this was with octane booster. I'll be trying more octane booster next week to see if this changes my readings.

I fill up 95 octane but I'm sure it's ****ty gas, you'll be surprised how much ****ty gas is around and people don't really notice it.

rselby

From what I have noticed with other cars I have had is that exhaust leaks at or near the header flange can cause the knock sensor to read this as knock( false knock )
or even the valve train being slightly loose can cause the sensors to pick this sound up and think it is spark knock.So your exhaust leak can cause it to have low numbers.
also I would get a AOS if you have any oil inside your intake, this will help to keep oil from getting mixed with the gas and lowering your octane

nks979

Yes the manifold crack is pretty common on higher mileage cars, I wasn't aware it could actually cause trouble besides losing a bit of power and making an annoying noise though?

DaOne54

I Know that the cracked manifold is obviously not a good thing, but since i compared numbers with another ISF with a cracked manifold as well, I would expect low numbers on both. BUT... maybe not, maybe mine is just slightly more cracked and is affecting it more than his.
I just didn't wanna spend the money on headers and then find out its all due because of low compression/bad bearings/bad engine mounts or whatever. Which is the reason why I was wondering if other people with cracked manifolds also had low knock learn values.

And yeah cracked manifolds are extremely common... they break even while still under warranty sometimes. Usually always the right side.

dcguy

Interesting read. I also have been unfortunately doomed with a low KC car as well. Been having issues with this ever since i've been able to see my values when the car was at 20k mi, I have just rolled over to 30k. You are not alone OP. I've seen my value down to 10.2 twice and knocks as hard as -8.8 on the sensors. Purchased the car 09 with 9k miles on it spring last year. Before I started data logging I do remember a butt dyno increase after resetting the ecu and wondering why. Highly doubting my manifolds are cracked, don't hear a tick or anything, car has low miles. I have been able to balance my KC out by keeping the car above 40 mph for a few minutes to bring down the intake temps close to ambient before any medium to hard acceleration, and never romp on it from an extended stop. The intake temps sky rocket and seem to take quite a bit of driving to get them back down. Also plagued with 91 octane as the max, was able to bring my values up with octane booster as well, into the 18s and max ive seen was 20.2. Hopefully we can all focus on this and come to a solution, seems to be a common problem with many of the F's I have personally datalogged.

dcguy

We've roll raced multiple low KC F's with High KC F's and the difference is fairly small just a slight pull with the advanced timing, nothing night and day.

Defratos

Well I guess it is a common problem, I stand corrected.

Are you using Tech stream to log your values? or a Bluetooth unit?

DaOne54

So octane booster does increase the knock learn values from your experience? In your case it seems like the octane you are using is actually the problem, if it was anything else I would expect the knock learn to stay the same even after adding octane boosters (for example false knock from valve lash/drive train/exhaust leaks/abnormal engine vibrations).
It sounds like high heat and not enough octane might be causing slight detonations causing the ignition to kick it down a notch.

I guess I'll try adding some octane boosters and some high octane fuel and report back seeing if it improved or not... and then if that doesn't make it any better I'll try a new manifold and go from there.


I actually have access to a factory toyota/lexus scan tool (TechStream laptop) thanks to a friend..Which is what I've been using.

wmjeffreyw

I had low numbers after adding RR Racings tune. Here in Az all we have is 91. The tune works best on 93 octane gas. Once I started using Royal Purple octane boost my numbers came up.

Manhitbytr

iTrader: (1)

I just got PPE headers done and when my old headers were taken out they cracked at the flange. Prior I was logging at high 19 to low 20s. I have the rr racing tune and notice the KCLV is really sensitive to heat soak. If you do a heavy load pull from a stop KCLV drops dramatically, and takes a while to get back up. Currently at 16.7 above 3k rpm but I have only been running the tune for 3 days but not much driving and building yet. Its really hot here now and my intakes are about 90*F so I see KCLV fluctuating a lot with the tune.