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1998 Subaru Legacy knock sensor

knock sensor legacy

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25 replies to this topic

#1 scoobywagon45

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Posted 29 April 2013 - 08:01 PM

My wagon has some leg in accelerating. It is a stick and around 2,000 rpms there is a lag, it does not want to go any faster. To me it feels like an auto tranny not wanting to downshift on a hill. After 3400 rpms the leg is gone and the power is back. It has a completely rebuilt engine, seals, gaskets, a new crank and one new rod. I found out the answer to this problem and it was the knock sensor. Below the knock sensor someone helped me place a small donut shaped gasket and this immedialetly fixed the problem. I just got a new knock sensor today and thought that it would solve the problem for good but it is back. The homemade gasket is not underneath the knock sensor. Has anyone had a problem like this and could it be part of the rebuilt engine?


Edited by scoobywagon45, 29 April 2013 - 08:01 PM.


#2 lmdew

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Posted 29 April 2013 - 08:30 PM

Is the CEL on?  If the Sensor is bad, you should get a CEL.  

 

Did the new sensor get properly clocked so it's setting flat?  

 

Did you read the resistance of new sensor before you installed it?

 

Just some thoughts.



#3 scoobywagon45

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Posted 29 April 2013 - 09:04 PM

the check engine light was on before then I reset the ecu, and installed the new sensor and it was torqued down to the correct amount. Could this be part of the ecu relearning timing?



#4 scoobywagon45

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Posted 30 April 2013 - 10:51 PM

I put the small gasket back on today and it seemed to fix it. It just worries me that it thinks that there is a knock.



#5 scoobywagon45

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Posted 01 May 2013 - 11:46 AM

Nevermind did not fix the problem, does anyone know what the torque is on it?



#6 mikaleda

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Posted 02 May 2013 - 08:24 PM

Hand tight plus a quarter turn, is what I torque knock sensors to. No gasket under the knock sensor that will cause problems since the - negative side is conects through the block. Make sure the sensor has a good clean connection to the block and is sitting flat. Also what code are you getting?

#7 scoobywagon45

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Posted 02 May 2013 - 11:03 PM

I dont what the number of the code was, someone else hooked up the reader. K thanks ill try it without the gasket underneath.



#8 Fairtax4me

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Posted 03 May 2013 - 12:04 AM

Pretty sure it's 17ft-lbs which is basically just snug. 1/4 turn after hand tight may be a bit too much. Hand tight, put your palm on the head of the ratchet and turn your wrist and it will be tight enough.

An actual code would be helpful.

Some other possibilities:
A dirty MAF sensor can cause hesitation like this.
Vacuum leaks.
A plugged PCV valve can cause all sorts of issues. When did it last get filters, plugs, and wires?

#9 scoobywagon45

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Posted 08 May 2013 - 11:52 AM

It has new everything, could this be part of the ecu? Everytime I reset the ecu it goes away for a little while and the it comes back again.



#10 mikaleda

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Posted 08 May 2013 - 12:24 PM

Are you getting a knock sensor code? If you are I would think its probably a bad wire to the sensor or maybe a dirty connection.

Edited by mikaleda, 08 May 2013 - 12:24 PM.


#11 Fairtax4me

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Posted 11 May 2013 - 11:18 PM

If the code is for the knock sensor it's a resistance issue with the circuit. The ECU either can't detect the sensor or the voltage signal is out of range due to poor connection or corrosion.

#12 scoobywagon45

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Posted 14 May 2013 - 12:23 AM

solved the problem!! I just moved the knock sensor to a new location. Its nice to have a car that finally has some power! Thanks for all the input!



#13 presslab

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Posted 14 May 2013 - 09:23 PM

Something in your engine is making a noise that is tripping the knock sensor.



#14 scoobywagon45

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Posted 15 May 2013 - 12:08 AM

nevermind it started back up again. could it be the rebuilt engine? everything just settling in still? 



#15 Fairtax4me

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Posted 15 May 2013 - 09:49 AM

Do you still have a CEL? It would be helpful to know exactly what codes are current. The issue may be due to another sensor.
If the current code is for the knock sensor it could be a faulty sensor.

#16 presslab

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Posted 15 May 2013 - 11:23 AM

Yes, you need to get the CEL code.

 

Does the engine sound quiet?  If it's got tappet noises you should check the valve lash.

 

The knock sensor is a microphone, it could be hearing other noises and thinking it's knock.



#17 scoobywagon45

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Posted 16 May 2013 - 07:10 PM

The code was for a knock sensor, I cleared it by resetting the ECU, there is a noise with the engine but it does not come up every time. I can only hear it while it is idling and it is very slight, could this be piston slap?



#18 mikaleda

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Posted 16 May 2013 - 07:12 PM

The code was for a knock sensor, I cleared it by resetting the ECU, there is a noise with the engine but it does not come up every time. I can only hear it while it is idling and it is very slight, could this be piston slap?


How long has it been since you adjusted the valves?

#19 scoobywagon45

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Posted 16 May 2013 - 08:03 PM

I dont know I was not the one who rebuilt the engine, I do know that some new valves were put in though. Could this be the problem?



#20 mikaleda

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Posted 17 May 2013 - 09:38 AM

It couldn't hut to check the adjustment

#21 Fairtax4me

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Posted 17 May 2013 - 10:11 PM

Need to know year and engine size to know if valve adjustment is even possible.
Still want to know if the current CEL is for the knock sensor.
I have a feeling it may be something else like a dirty MAF sensor or maybe even a misfire because of fouled or old spark plugs.
If the code is still for the knock sensor it's either a wiring issue or a bad sensor.

#22 mikaleda

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Posted 17 May 2013 - 10:18 PM

Title 98 legacy, interferance adjustable valve clearance.

#23 scoobywagon45

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Posted 20 May 2013 - 04:41 PM

I cleared the CEL and it was for a knock sensor, I moved it up a bit to where the clutch cable goes by and that diminished the lag a lot. Going to move it to another place if I can. 



#24 Fairtax4me

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Posted 20 May 2013 - 09:04 PM


If the code is still for the knock sensor it's either a wiring issue or a bad sensor.



#25 scoobywagon45

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Posted 20 May 2013 - 09:47 PM

The code went away when I cleared it for the first time, it hasn't come back since, sorry I should have clarified that.






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