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Unread 03-21-2013, 04:44 PM   #1
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Knock Sensor throwing code

So I posted this in the XJ forums first since my 4.0 is technically out of an XJ, but doing some more research, it sounds like 91-98 4.0s are pretty much similar enough that maybe someone here can help. I haven't had much help from the XJ guys.

Original Post:
Hey all,
I'm looking for some advise on how to troubleshoot the knock sensor. I have a 93 YJ with a 4.0 HO out of an XJ. It runs pretty good the majority of the time with no problems. The only noticeable problems I seem to be having is a slight hesitation with acceleration/shifting (AW4 trans) if I don't let it warm up for a few minutes before taking off, as well as below average fuel economy.

At highway speeds, the idiot light comes on. No noticeable change in the vehicles behavior though when it does, and it only pop's the CEL at higher speeds (maybe 50mph+).

So today I pulled the codes, and the only trouble code I have is listed as "knock sensor inactive" (code44). What does that even mean? Since I have a Painless harnes/ECU I use their codes and not the stock codes. I did some google-fuing as well as some searching on here and couldn't seem to find a method of troubleshooting the problem.

Here is my trouble code list, copied from the Painless manual.
Code # Circuit affected
13 Oxygen Sensor
14 Coolant Temp. High Voltage (COLD)
15 Coolant Temp. Low Voltage (HOT)
21 Throttle Position Sensor (high voltage)
22 Throttle Position Sensor (low voltage)
23 Intake Air Temp. Low Voltage (HOT)
25 Intake Air Temp. High Voltage (COLD)
33 MAP Sensor Circuit (high voltage)
34 MAP Sensor Circuit (low voltage)
41 Ignition Control Circuit (open IC circuit)
42 Ignition Control Circuit (grounded IC)
44 Knock Sensor Inactive
54 Heated Oxygen Low Voltage (lean)
55 Heated Oxygen High Voltage (rich)

Any advice would be more than welcome. I can't quite figure this out. I checked all the connections with a muti-meter and they are all good/getting power/signal where they should. The knock sensor itself is brand new (came with the painless kit, only about a year and a half old.)

I'm starting to wonder if, because of how bad my suspension is, coupled with the alternator whine, and the loud exhaust, that the knock sensor is just picking up way too much background "noise?" Any thoughts on this?
Thanks in advance!

Cheers

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Unread 03-21-2013, 07:16 PM   #2
laybackman
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Quote:
Originally Posted by Sparrows View Post
So I posted this in the XJ forums first since my 4.0 is technically out of an XJ, but doing some more research, it sounds like 91-98 4.0s are pretty much similar enough that maybe someone here can help. I haven't had much help from the XJ guys.

Original Post:
Hey all,
I'm looking for some advise on how to troubleshoot the knock sensor. I have a 93 YJ with a 4.0 HO out of an XJ. It runs pretty good the majority of the time with no problems. The only noticeable problems I seem to be having is a slight hesitation with acceleration/shifting (AW4 trans) if I don't let it warm up for a few minutes before taking off, as well as below average fuel economy.

At highway speeds, the idiot light comes on. No noticeable change in the vehicles behavior though when it does, and it only pop's the CEL at higher speeds (maybe 50mph+).

So today I pulled the codes, and the only trouble code I have is listed as "knock sensor inactive" (code44). What does that even mean? Since I have a Painless harnes/ECU I use their codes and not the stock codes. I did some google-fuing as well as some searching on here and couldn't seem to find a method of troubleshooting the problem.

Here is my trouble code list, copied from the Painless manual.
Code # Circuit affected
13 Oxygen Sensor
14 Coolant Temp. High Voltage (COLD)
15 Coolant Temp. Low Voltage (HOT)
21 Throttle Position Sensor (high voltage)
22 Throttle Position Sensor (low voltage)
23 Intake Air Temp. Low Voltage (HOT)
25 Intake Air Temp. High Voltage (COLD)
33 MAP Sensor Circuit (high voltage)
34 MAP Sensor Circuit (low voltage)
41 Ignition Control Circuit (open IC circuit)
42 Ignition Control Circuit (grounded IC)
44 Knock Sensor Inactive
54 Heated Oxygen Low Voltage (lean)
55 Heated Oxygen High Voltage (rich)

Any advice would be more than welcome. I can't quite figure this out. I checked all the connections with a muti-meter and they are all good/getting power/signal where they should. The knock sensor itself is brand new (came with the painless kit, only about a year and a half old.)

I'm starting to wonder if, because of how bad my suspension is, coupled with the alternator whine, and the loud exhaust, that the knock sensor is just picking up way too much background "noise?" Any thoughts on this?
Thanks in advance!

Cheers
Haven't we talked about this before?? Unscrew the knock sensor wrap the threads with PVC tape screw it back in an see if that 'fixes' the issue. Your knock sensor can 'hear' too well, or it needs to be replaced.

EDIT!! Orrrrrr, you got a knock in your engine
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Unread 03-21-2013, 07:28 PM   #3
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Quote:
Originally Posted by laybackman View Post
Haven't we talked about this before?? Unscrew the knock sensor wrap the threads with PVC tape screw it back in an see if that 'fixes' the issue. Your knock sensor can 'hear' too well, or it needs to be replaced.

EDIT!! Orrrrrr, you got a knock in your engine
Actually we talked about a similar problem, which I got fixed
I'll look back through that thread though, maybe you suggested this but I missed it.

Thanks though. I'll get that done tomorrow and report back in.

Cheers
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Unread 03-21-2013, 07:31 PM   #4
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Quote:
Originally Posted by Sparrows View Post
Actually we talked about a similar problem, which I got fixed
I'll look back through that thread though, maybe you suggested this but I missed it.

Thanks though. I'll get that done tomorrow and report back in.

Cheers
ORRR someone else posted a similar question and I got you mixed up with the other poster!!!!!!!!!
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Unread 03-21-2013, 10:10 PM   #5
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Quote:
Originally Posted by laybackman View Post
ORRR someone else posted a similar question and I got you mixed up with the other poster!!!!!!!!!
Oh hahaha! I was having a similar problem about a month+ ago. I was running at super high RPM and throwing codes at freeway speeds. It ended up being a combination of things. Bad 02 sensor that I replaced. I then cleaned the Throttle body and related parts and got the rpms down to a reasonable range.

Now it's throwing codes at freeway speeds again :

Anyways, thanks for the advise, I'll take care of it tomorrow and report back with results.

Cheers
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Unread 03-21-2013, 10:32 PM   #6
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Quote:
Originally Posted by Sparrows

Oh hahaha! I was having a similar problem about a month+ ago. I was running at super high RPM and throwing codes at freeway speeds. It ended up being a combination of things. Bad 02 sensor that I replaced. I then cleaned the Throttle body and related parts and got the rpms down to a reasonable range.

Now it's throwing codes at freeway speeds again :

Anyways, thanks for the advise, I'll take care of it tomorrow and report back with results.

Cheers
My advice, even if its only worth .02c, take the knock sensor out of the block. Plug the hole it came from. Then tie the knock sensor up by the firewall. Pointless sensor anyways.

Check your timing, plugs wires cap etc for any misfiring or evidence that may cause it. (If it is a miss it'd probably throw a code for that also though)
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Unread 03-21-2013, 10:59 PM   #7
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Quote:
Originally Posted by squishy View Post
My advice, even if its only worth .02c, take the knock sensor out of the block. Plug the hole it came from. Then tie the knock sensor up by the firewall. Pointless sensor anyways.

Check your timing, plugs wires cap etc for any misfiring or evidence that may cause it. (If it is a miss it'd probably throw a code for that also though)
Can you elaborate how this would work? I don't mind disconnecting it tomorrow and seeing what happens as long as it's not going to trash my motor. Maybe I don't understand it correctly, but I thought that the knock sensor is used by the computer to adjust timing. Something along the lines that the computer keeps advancing the timing until the knock sensor detects a "ping" or "knock" or whatever, and then it retards it just a bit from there. More or less it waits until it detects minor detonation in the cylinder and then adjusts from there.

So without it, couldn't the ECU just keep advancing the timing until I'm getting mad detonation and trashing/melting/burning up pistons and rings and all that? Or maybe it would go the other way and never advance the timing enough (since it knows it can't detect detonation) and it would run all bogged down?

Just my thoughts on it.

Cheers
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Unread 03-21-2013, 11:23 PM   #8
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Quote:
Originally Posted by Sparrows

Can you elaborate how this would work? I don't mind disconnecting it tomorrow and seeing what happens as long as it's not going to trash my motor. Maybe I don't understand it correctly, but I thought that the knock sensor is used by the computer to adjust timing. Something along the lines that the computer keeps advancing the timing until the knock sensor detects a "ping" or "knock" or whatever, and then it retards it just a bit from there. More or less it waits until it detects minor detonation in the cylinder and then adjusts from there.

So without it, couldn't the ECU just keep advancing the timing until I'm getting mad detonation and trashing/melting/burning up pistons and rings and all that? Or maybe it would go the other way and never advance the timing enough (since it knows it can't detect detonation) and it would run all bogged down?

Just my thoughts on it.

Cheers
Half right. The knock sensor does adjust timing but not unless it feels a "knock" like during a cold start or predetonation. And no your motor won't run away and blow up lol. If the timing goes to advanced or retarded it'll just die or run rough which you can fix the timing accordingly

I don't mean disconnect it completely. I had a 88 4runner and the knock sensor kept giving me problems, and at like $120 a pop And being under the manifold between the heads making it an hour + job, so I disconnected the plug from the one in the block, plugged in the new one and zip tied it to my firewall. Problems went away and I never dealt with it again.
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Unread 03-22-2013, 06:21 AM   #9
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Quote:
Originally Posted by squishy View Post
Half right. The knock sensor does adjust timing but not unless it feels a "knock" like during a cold start or predetonation. And no your motor won't run away and blow up lol. If the timing goes to advanced or retarded it'll just die or run rough which you can fix the timing accordingly

I don't mean disconnect it completely. I had a 88 4runner and the knock sensor kept giving me problems, and at like $120 a pop And being under the manifold between the heads making it an hour + job, so I disconnected the plug from the one in the block, plugged in the new one and zip tied it to my firewall. Problems went away and I never dealt with it again.
That is a good fix also.

If your upper drivetrain is getting 'noisy' the knock sensor may pick up the noise and start messing with your timing etc. thinking it is hearing pre-detonation. Isolating the knock sensor could make the false problem go away
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Unread 03-27-2013, 11:12 PM   #10
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Quote:
Originally Posted by laybackman View Post
That is a good fix also.

If your upper drivetrain is getting 'noisy' the knock sensor may pick up the noise and start messing with your timing etc. thinking it is hearing pre-detonation. Isolating the knock sensor could make the false problem go away
Forgot to update this. whoops!
I got around to taping the knock sensor and clearing the codes. Didn't do much driving for a few days, and then BAM! Throwing the same code with the same symptoms. Taching high at highway speeds.

I'll try just disco'ing it next.

Can someone explain to me how the knock sensor being "off" would raise the RPM's so much? I'm not quite sure I understand it fully. It's the only code I'm getting and the only time I have the problem with high RPM at freeway speeds now is when the code pops. I'm befuddled.

Cheers
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Unread 03-27-2013, 11:30 PM   #11
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Quote:
Originally Posted by Sparrows

Forgot to update this. whoops!
I got around to taping the knock sensor and clearing the codes. Didn't do much driving for a few days, and then BAM!

I'll try just disco'ing it next.

Can someone explain to me how the knock sensor being "off" would raise the RPM's so much?

Cheers
You did what to the sensor?

Don't disconnect it just take the sensor STILL PLUGGED IN and "isolate" it from the engine somewhere it doesn't move or bang or contact anything. You may have to tape it or zip tie it to something good and tight.
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Unread 03-27-2013, 11:36 PM   #12
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I did this
Quote:
Originally Posted by laybackman View Post
Unscrew the knock sensor wrap the threads with PVC tape screw it back in an see if that 'fixes' the issue. Your knock sensor can 'hear' too well, or it needs to be replaced.
And thats what I meant by disconnect it; follow your previous advice. I'll give it a try.

Could the knock sensor be causing my current RPM issue? That's the part I can't seem to find an answer to. When I first bought the YJ it was doing a similar thing, but after cleaning the TB and all related parts, it stopped for a while. Now it's doing it again and this time the computer is blaming the knock sensor.

So, can the knock sensor cause my 4.0/aw4 to run about 700rpm higher than normal?

Thanks for the continued support.
cheers
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Unread 03-28-2013, 06:10 AM   #13
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Originally Posted by Sparrows View Post
I did this


And thats what I meant by disconnect it; follow your previous advice. I'll give it a try.

Could the knock sensor be causing my current RPM issue? That's the part I can't seem to find an answer to. When I first bought the YJ it was doing a similar thing, but after cleaning the TB and all related parts, it stopped for a while. Now it's doing it again and this time the computer is blaming the knock sensor.

So, can the knock sensor cause my 4.0/aw4 to run about 700rpm higher than normal?

Thanks for the continued support.
cheers
Yes. The knock sensor was installed to 'listen' for early spark detonation, AKA spark knock. It will advance your timing and the RPM's of the engine also. The electronics is attempting to fix a problem that does not exist.

You know what happens if you climb a steep hill in your rig and your rpms are not high enough? You bog the engine. The engine will knock and even stall IF you not downshift increasing engine rpm's. Then the knock sensor gets involved for a problem that has nothing to do with the job of the knock sensor.

If your timing is too advanced knock can occur.

It can happen if you are running too lean also, since the cylinders get very hot because not only does the air fuel mix burn, it quenches the cylinder cooling the valves and upper cylinder off.

If the valves/upper cylinder(s) get too hot, as soon as the air fuel mix is allowed into the cylinder it ignites (pre-ignition). At that time the piston has not made it to TDC and the intake valve is still open. That explosion works AGAINST the rotation of the crank and you get a back fire through the throttle body or carburetor. Since it is igniting before the piston is where it needs to be and the valve(s) are still not closed. Sometimes this can happen after the point where ignition should occur and you get a backfire through the exhaust losing power and 'alerting' the knock sensor to a problem that does not exist. Even running premium fuel in an engine designed for low octane fuel could cause knock.

Make sure the spark plugs you are running are in the right heat range also for your engine. Stick with the regular plugs like Champion or Autolite.

The simplist fix is to plug the knock sensor boss with a plumbers plug (1/2"?) and place find a new place for the plugged in knock sensor to be, wrapped in anything to make it 'hard of hearing".
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Unread 03-28-2013, 08:52 AM   #14
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Thank you so freaking much!
I've been having a hard time "visualizing" how it all plays together. I know what the knock sensor does, but not how it related to the "big picture." I'm pretty damn new at doing all my own maintenance and my biggest problem is that I'm weak at diagnosis since I still don't fully understand how each part works together. I can identify most parts, and know their basic function, but I'm still learning via "crash course" of just digging in and trying.

You just managed to answer all my questions and make it "click" in my mind. I've called a few local shops and none of them were able/willing to give me an answer, so I was getting pretty frustrated. My goal is to be able to eventually be able to tear apart any part of my Jeep, fix it, and put it all back together myself. Learning curve....

I freaking, no homo, love you right now

I'm headed out to the JY today to snag some misc parts and hunt for an 8.8. Hopefully tonight I'll be able to do as you suggest. I'll report back in once I do. Thanks a million man.

Cheers
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Unread 03-28-2013, 09:03 AM   #15
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Quote:
Originally Posted by Sparrows View Post
Thank you so freaking much!
I've been having a hard time "visualizing" how it all plays together. I know what the knock sensor does, but not how it related to the "big picture." I'm pretty damn new at doing all my own maintenance and my biggest problem is that I'm weak at diagnosis since I still don't fully understand how each part works together. I can identify most parts, and know their basic function, but I'm still learning via "crash course" of just digging in and trying.

You just managed to answer all my questions and make it "click" in my mind. I've called a few local shops and none of them were able/willing to give me an answer, so I was getting pretty frustrated. My goal is to be able to eventually be able to tear apart any part of my Jeep, fix it, and put it all back together myself. Learning curve....

I freaking, no homo, love you right now

I'm headed out to the JY today to snag some misc parts and hunt for an 8.8. Hopefully tonight I'll be able to do as you suggest. I'll report back in once I do. Thanks a million man.

Cheers
If you cannot visualize how things or why things work you cannot be able to analyze what is going wrong with your vehicle...or anything else!
You realize that and that puts you way ahead of where you were a few days ago.

I strongly advocate buying an FSM for every vehicle you own. You can read how things are put together and why they are put together and what their purpose is. IMHO it is THE BEST tool you will ever buy EVEN if you have a mechanic fix your vehicle.
The knowledge you gain can keep more of your money in your pocket!!
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