Sorry for yet another knock sensor thread, but I've been reading for a while and haven't found any answers.

I have the 0304 knock sensor code with no other codes, but I can't figure out the problem. I bought and replaced the knock sensor before measuring resistance of the old one (stupid, I know), but this did not resolve the issue.

Here are the details:
*I can measure resistance between the subharness connector and ground at 550 kOhms.
*I measured the resistance of both the old and the new knock sensors directly. Both were at 550 kOhms.
*Both knock sensors visually look okay (no cracks).
*If I reset the ECU, the code disappears and I get the 0505 (no problems) for a little while. However, within 30 miles of driving, 0304 comes back.
*If I reset the ECU which the subharness disconnected, 0304 comes back immediately.
*I don't notice any knocking while driving.
*After resetting the ECU, hard acceleration feels smooth up to redline. After driving for about 20 miles, I'll start feeling short (< 0.5 sec) dips in power during hard acceleration. I didn't pay attention if this always occurs at the same RPM.
*I bought the new knock sensor off of ebay, but it appears to be a new and genuine Nissan part.
*I cleaned off the ground points for the KS.
*I don't think I overtightened the KS bolt. I hand tightened the bolt, then used a wrench to turn the bolt slightly more.
*I always use 91 octane.
*Only mods are y-pipe and suspension parts.

Could it be the subharness? I haven't replaced it, but I assumed that since I can measure the KS resistance between the connector and ground that the subharness is okay.

Please let me know if anyone has any other ideas.

TIA!

 

bump...

 

i'm guessing bad KS. ohm test not always definitive.

are you absolutely sure you feel a difference in power after 20 miles, or is it just placebo? could also be the injector trim kicking in as the ECU learns it's new fuel map after the reset.

 

KS should go away after replacing KS and resetting ECU. U sure the wire not shorted somewhere. Check the harness as well. Throw so Chevron Techron in the tank too. Let it work its magic

 

cdmapro,
I've replaced the old KS with a new one, so I highly doubt the KS is still bad.

The power dips are obvious since they're instantaneous. For the most part, the car accelerates normally except for a 0.5 second period where the power just drops off and then comes back up to normal. You notice it right away. However, I admit that the smooth acceleration after resetting the ECU may be a placebo. I haven't tried it enough times to know for certain.

cashoit,
The KS code goes away after resetting the ECU, but only for a short while (less than 30 miles of driving).

I'm not certain that the harness is or is not bad somewhere, but I'm guessing that if the harness was bad, two things would happen:
1) The ECU would give me the 0304 immediately (similar to my test cases where I left the subharness disconnected and reset the ECU) rather than after some driving delay.
2) I wouldn't get the 550 kOhm reading at the subharness connector.
If you can tell me any sure fire ways of testing the harnesses, that'd be appreciated.

Also, I run a bottle of Techron concentrate through before each oil change. I have also done a round of Auto-RX before.

Thanks for your input guys!

 

I just found these instructions from the FSM posted in another thread:
-------------------------------------------------------------------
From FSM
Knock Sensor Diagnostic Procedure

1. Loosen and retighten engine ground screws (front of intake manifold)

2. Check input signal circuit - 1
Ignition OFF
Disconnect ECM harness and knock sensor sub-harness
Check continunity between terminal 1 of sub harness (connector on top, left pin) and ECM terminal 64
Continunity should exist
If OK check harness for short

3. Check input signal circuit - 2
Check resistance between terminal 1 and engine ground
Resistance appx. 500 - 620 K omh
If OK check harness for short

Inspect knock sensor
Check resistance between terminal 2 (left pin) and ground
Appx 500 - 620 K omh @ 77 degrees
-------------------------------------------------------------------

Perhaps my harness is bad because I can only measure 550 kOhms from one of the connector pins (the top/left pin) and not the other. I've always seen instructions to only check the left pin so I though my harness was okay.

Can anyone confirm that I'm supposed to be able to measure the same resistance with the right pin?

 

i think the techron suggestion was sarcasm.

KS is very fragile. if dropped the piezoelectric element will shatter and you can't tell by ohming it. since it came from ebay you have no idea what may have happened to it before you.

go ahead and check your harness. if it's fine buy another KS from a dealer.

 

Okay, back to the drawing board. I did more searching, and it seems that measuring between pin #1 and ground should indeed be an open circuit. From Daniel B. Martin:

If I don't get any other suggestions, I guess I'll just try replacing the harness, then the KS again as you suggested.

 

That is not a symptom of the KS.

You have something else going on and for some reason your ECU is throwing the KS code. You may have pending codes, drive it some more and keep checking for another code to pop up along with the KS. Do not keep clearing the codes!!!

 

You may be right that there is a different root cause other than KS issues, but I probably won't get any codes regardless of how long I drive. I've actually had 0304 since at least March, but I've only recently gotten around to changing the KS. I checked the ECU right before changing the KS, and 0304 was still the only code presented.

Maybe I'll just take the car to an actual mechanic...

 

You have something else that the ECU is trying to pinpoint but it may take some time to throw a code. I can't clear mine also and I replaced the KS. I have a slight misfire so I know one of the coils are on the way out.

 

I am getting this exact same problem in my '96 I30. This occurs at around 40mph (I forgot what the tach read, but the hesitation I get seems speed dependent).

I have an O2 sensor code and the knock sensor code. I have a "ticking" sound at idle. Car does not overheat.