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View Full Version : PFC reading knock with and without knock sensor !


nickauger
07-15-2013, 11:48 AM
Ok guys I've bring my car to my tuner last week and he notice that my knock sensor seems inaccurate. It is reading a lot of knock at idle then nothing then again. So I've done a few test today I disconnected the knock sensor to see if it stop reading knock.

My power fc read more knock when the knock sensor is unplugged ?

And it is reacting the same way that when it is plugged.

I've test harness for short to ground , continuity and OHM reading.

I think it can be electronic interference (magnetic phenomena ) maybe ?

Any help would be appreciate

Thanks

fliprayzin240sx
07-15-2013, 10:31 PM
How many knocks is "a lot of knocks"?

inopsey
07-16-2013, 03:55 PM
the pfc isnt able to properly filter the knock sensor to give an accurate reading of knock. the knock feature on the pfc is more of a novelty feature than anything

Kingtal0n
07-16-2013, 04:36 PM
the pfc isnt able to properly filter the knock sensor to give an accurate reading of knock. the knock feature on the pfc is more of a novelty feature than anything

wtf? it works perfectly fine. Just today I am watching my engine noise charts off my power FC both increments and they work exactly like they should.
Never tune without it.

inopsey
07-17-2013, 01:21 PM
if you were to use a real knock device (knock headphones) you would see that the pfc isnt effective at picking up knock. take a look at your spark plugs bet they show signs of detonation if your relying on the pfc to pick up knock.

nickauger
07-17-2013, 04:11 PM
My spark plug are perfectly fine , I just don't understand why I have knock at idle... my timing is spot on 15*, and it is idling fine ... some small misfire but nothing major. I think i have a problem because if I disconnect the knock sensor it is still reading knock...

Kingtal0n
07-17-2013, 06:00 PM
My spark plug are perfectly fine , I just don't understand why I have knock at idle... my timing is spot on 15*, and it is idling fine ... some small misfire but nothing major. I think i have a problem because if I disconnect the knock sensor it is still reading knock...

the knock sensor is just a noise sensor. it picks up noise in whatever frequency range its designed to. Output readings are given in "noise per unit time of the given frequency" so higher knock counts means more instantaneous counts of noise. There are also two protocols for knock output by the power FC, you have a way to distinguish between two different settings if using the data-logit.

which I am thinking you do NOT have. So you are only looking at the commander for knock reading?

Questions to you
1. was the knock sensor ever changed or removed from the engine.
2. how much knock count is the reading say, what is the lowest and highest numbers you see.
3. describe all knock numbers for idle, driving, cruise, wot, etc...

nickauger
07-21-2013, 04:57 PM
Before doing any of teh below check the component itself by checking the resistance of teh knock sesnor, a good knock sensor reads 560 Mega Ohms thats 560,000,000 ohms

Now you can proceed!

Well I fixed my knock sensor error code problem.

After spending many hours actually days on this sh*t I finally fixed the problem and the ECU now gives me a code 55 ......

Heres are the diagnosis steps I performed:

1. Disconnect ECM harness connector from ECM.
2. Disconnect KS subharness connector from KS.
3. Check harness continuity between terminal (B) and ECM terminal (27).

Im my case continuity did exist (so good to go right? NOPE) im still getting a code 34 and my knock sesnor is good to go.

Next I pluged everything back together like it should be then:

Step:
1) With a DMM, one probe to ground other back probing pin 27 (Knock Sensor) with KOER and KOEO.

Results = 0.013v (no good) FSM states you should see aprox. 2.5v at idle and or KOEO.

2) I disconnect ECM harness connector from ECM and de-pin, pin 27 from harness connector alltogether.
3) I re-attach the ECM harness connector to the ECM with pin 27 detached from connector.
4) With my DMM I ground one probe and the other to pin 27 and I get 5v, so the ECU is good to go.

So next step:
1) Taking a jumper wire to pin 27 and reconnecting the original (white) KS wire to the jumper wire I instantly lose the 5v (so im thinking why what is causing this to happen (a short to ground etc etc)
2) I take the same jumper wire and disconnect the original (white) KS wire from it and get about 3ft of regular 16 gauge wire and run it directly to the knock sensor subharness terminal (B).
3) I take measurements back at the ECM with my DMM one probe to ground other to pin 27 and I get 2.5v (good to go finally
4) So now I clear the codes and start the car run it for a few seconds and shut it off.
5) Check codes for any errors and all is good (code 55 finally)

If some of you are wondering why I didn't get 5volts when I rewired, its becasue the KS itself is a 0.560M-Ohm resistor and it reduces the voltage down to approx. ~2.5v.

My code 34 was instantanious means I could clear the codes and get code 55, start the car for 1 second then turn it off and check teh codes and I have a code 34, thats becasue it basically had no voltage present of pin 27.

nickauger
07-21-2013, 04:59 PM
Will try this next weekend ! Probably a bad wiring ! Thanks to Chasebays Harness ...

aga
08-01-2013, 03:55 AM
How many knocks is "a lot of knocks"?

for idle, more than 5-10

for cruising , more than 20

for full throttle more than 40

originally the power fc flashes the check engine light over 60 by default, but by judging by the charts on the datalogging, over 40-50, its a knock. most of these are not engine damaging, cause the FC is preety sensitive, but prolonged use like that and idontgiveafuckism, will result in engine damage. or at least in a friends case, pistons with a lot of small pits (which will result in even more knocks, cause they heat up and cause detonation)

fliprayzin240sx
08-01-2013, 11:28 AM
for idle, more than 5-10

for cruising , more than 20

for full throttle more than 40

originally the power fc flashes the check engine light over 60 by default, but by judging by the charts on the datalogging, over 40-50, its a knock. most of these are not engine damaging, cause the FC is preety sensitive, but prolonged use like that and idontgiveafuckism, will result in engine damage. or at least in a friends case, pistons with a lot of small pits (which will result in even more knocks, cause they heat up and cause detonation)

Yup, I agree. My PFC, most I'd see on a really hot day is about 36. Once it gets close to 60, I'd start plugging in my damn laptop and do some datalogging to see where the knock is happening to pull some timing in the map or add some more temp correction.

aga
08-02-2013, 01:38 AM
mine sometimes bangs 70-80 when the VTC kicks in yo. but usually 25-30 is the max it will go

fliprayzin240sx
08-03-2013, 05:29 PM
Yah, I'd get a dataloggit and figure out where its knocking, check the AFR around where its knocking on the cell and probably pull some timing if the AFR is good.

EsChassisLove
08-03-2013, 07:33 PM
My old PFC setup would hit 140+ knock on the reader on a T25 at 7psi with 93oct.


I never even bothered with that stupid piece of inaccurate shit.

aga
08-04-2013, 04:16 AM
its highly accurate, in my opinion. maybe oversensitive. but a certain car that was still runnning in , i warned him not to boost it cause i had tuned only up to zero boost, to drive around and run in the engine, 5 minutes later he raced a yamaha R1... a month later we open up the engine (cause of rod knock) and the pistons are pitted. when the ecu says "knock here" and you reduce the ignition advance and it stops, what does it mean? that it's inaccurate? sorry but no.

Kingtal0n
08-04-2013, 04:32 PM
Ive tuned at least 20 power FC sr20 cars. the highest knock I see when I am done is around 17 MAX. I usually wind up around 12-13 peak after a wide open throttle run in a 400 horsepower car. Cruising highest I usually see is 5 or 6 but it normally stays around 4.
Idle should be 1 or 2. taking off from a light, 2 or 3.

they are usually very accurate noise sensors when installed right. Actual knock comes in different forms. Theres the pre-ignition that will set the knock sensor off and bring you overall count up but it is completely inaudible to the human ear and many people ignore it. Its hard to see with a commander but with the data-logit you can just look at the chart and tell there is something wrong.

nickauger
08-09-2013, 01:34 PM
Ok i've done some test today, my PFC output (pin 27) knock sensor is only sending 0.4V and with original sr20det 62 ECU I have 4.5V

So is it my PFC that is fucked up or it is just different than normal ecu ?

nickauger
08-10-2013, 09:03 PM
help please, anybody can tell me what voltage the PFC is supposed to output to Knock sensor ?

nickauger
08-12-2013, 02:17 PM
Anyone ????