Knock Senor Error Issues

[crazymilk]

I am having a real issue trying to diagnose this knock sensor fault on my 2000 Subaru Ej251 Outback 

The code number is #22 with the CEL and terrible performance under load. 

So to outline so far:
Tried new knock sensor, correct torque and alignment according to FSM – still light. Have checked both the old and new sensors and both working correctly (Mulitimeter test confirmed this)
Have checked the continuity of the wiring from the knock sensor back to the ECU - all OK.
Checked timing belt all ok
Cleaned and checked the knock sensor mounting face of the block several times
Checked all earths on block to chassis
Checked Valve clearances on heads
Checked correct injector plugs plugged in to correct injectors as per colour wires in FSM
Compression test on all cylinders ( all around 170psi and all within 10psi of each other)
Checked to make sure no loose items around the block knocking about

As far as I know the knock sensor will throw a code if it detects improper ignition/detonation within one or more cylinders (so effectively the timing of the ignition of fuel and air). Basically the ECU has been told by the Knock sensor something is not firing correctly so retards the engine which results in poor performance.

Once I clear the code (by unplugging the battery overnight) as soon as I restart the engine the CEL comes on immediately. (again always error code#22)
The van starts on the button every time and initially sits on tick over perfectly on all cylinders, revs up well and sounds good.(albeit with the CEL light on) 

Am I right in thinking that once I have cleared the codes by unplugging the battery overnight, once I restart the engine the ECU will start the engine in learning mode, it will push the ignition timing to the point of knock and then limited it back to the correct timing level it deems to be optimum safe levels (although it will not throw a code/light in this learning process). Therefore why is the light coming on immediately I start the engine after a reset?
The only other thing I can think of is if it related to a dodgy coil pack, ignition leads or spark plugs? Is it worth swapping this out or not? 

Lastly it is annoying as **** to wait 12 hours with the battery discounted every time I try something to clear the codes. I have read about FreeSSM with the correct USB/OBD connector (seem on ebay link below ). Would this work or would a stand-alone reader be better (and if so which one).

https://www.ebay.co.uk/itm/Fits-Suba...m/323766582087


I am sorry for the long winded email however I hope this detail might be useful in finding/solving this problem I didn’t have before I took the engine out.


I almost gave in and bought a new recondition block for stupid money thinking the engine is totally knackered/worn but I’m not going to give up on it just yet.

Any helps or anything I have missed would be great.

I am reading the code from plugging in the 2 x black connectors and I am getting two long flashes from the CEL and two short flashes. This equated to error code 22 which I believe will read PO325 using a scanner.
Just one that I am trying to the my head around and be clear on.

Does the knock sensor only monitor for ignition/combustion irregularities or for other mechanical knocks as well including worn bearing/shims ect.

The car does not support OBD2, only OBD1

 

[heartless]

you do not need to wait 12 hours after disconnecting the battery to clear codes.. 30 minutes to 1 hour should be sufficient.

Seeing as how plugs and wires are an important part of ignition, you may want to take a closer look at those.

how old are the plugs? what condition are they in? brand & type? Subarus like simple NGK copper core plugs - nothing fancy is needed here.

Wires should be either OEM (Subaru) or NGK brand - aftermarket parts store brand wires are known to cause problems and should be avoided at all costs.

Quote

The car does not support OBD2, only OBD1

if it has an OBD port, it supports OBDII - not sure where you got this idea from. OBDII started in 1996...

Pretty much any OBDII reader will handle basic code reading.

[el_freddo]

Have you checked the cam belt timing at both cams? The LHS one is the most important as it has the cam angle sensor. If this is out it may cause timing issues that could lead to a detonation issue that could possibly throw a code. 

I do the “battery dance” for 30 mins to clear the codes. 

On cold start up, there’s no knocking in the bottom end? 

Cheers 

Bennie

[GeneralDisorder]

The code is for a circuit fault. It has NOTHING to do with actual detonation. And detonation (no matter how severe) will NEVER set a code of any kind.

Bad sensor, bad wiring, or bad ECU. Those are the ONLY causes of that code. And once the fault is resolved the code will IMMEDIATELY clear itself and stay off. If you start the engine and it throws a knock sensor code then the circuit fault is NOT resolved. 

As to sensor function - the knock sensor is a microphone. Tuned to a specific frequency that is chosen by the engineers to be appropriate for that specific engine - usually this is a calculation based on bore diameter, etc. It generates a voltage signal that is then filtered and interpreted by the ECU's hardware and software. The cylinder responsible for the detonation event is calculated by crankshaft position and attenuation due to distance from the sensor. Detonation results in timing being retarded but will NEVER set a code. A circuit fault will result in a substitute "limp mode" timing map being applied that has less timing throughout leading to a reduction in fuel economy and power but with NO trouble code.  

GD

Edited April 25, 2019 by GeneralDisorder

[FerGloyale]

you need to get  code read with a OBD II scanner.  Code 22 for older OBD cars may not be the same as your OBD II car.  You need the POxxxx # from an obd II reader.  go to an autozone they will scan it or buy a cheapo $35-$50 simple OBD II scanner.

And clear the code with a Scanner as well.

Some codes will stay stored as pending even after battery disconnect.

Poor response under load can often be bad spark plugs in this engine.  Change them with NGK or Denso plugs only. $3.99 Iridium is fine.  no need for platinum.