Knock Sensor Question (1 Viewer)

[Mr. Toad]

1997 FZJ80. Here are the symptoms:

1) Pinging while cruising at highway RPMs in warmer weather.
2) Pinging stops when you let off the gas slightly or slightly give it some gas (both of which I believe are manually triggering timing adjustments).
3) No CEL

It's been doing this for a while. I'd like to know if anyone has experienced these symptoms and they turned-out to be caused by a malfunctioning knock sensor. If so, I'll go after the sensor(s), but every thread I've read regarding knock sensors involves CEL signals or broken wires, neither of which I have. My thoughts are that the ECU thinks the sensors are working fine but at least one is not sending any knock signal.

Carbon/EGR stuff has been cleaned out recently, so I don't think it's likely to be carbon pre-detonation.

Any ideas?

 

[elhombre]

Was the carbon cleaned out with a chemical or was the head off and the top of the pistons and fire ring cleaned off with a wire brush? Something else to consider is, at least in my area, we now can only get the ethenol blend crap gas.

I would check the timing first because that is an easy starting place.

 

[Mr. Toad]

thanks elhombre. Timing's perfect per FSM. The head has never been off.

 

[TrickyT]

Can you borrow a Scan Gauge or some other real-time OBD II application from someone? Ignition timing is one of the gauges on the Scan Gauge, so you could monitor timing and see if/how much it's really changing when you step on/off the gas.

Not sure what to say on the knock sensors. According the the FSM, they produce a signal under normal operating conditions based on their normal mode vibration frequency and then if they detect engine knock produce a signal that's either higher voltage or a different frequency (FSM doesn't specify which) so that the ECU can retard the timing. Sounds pretty much like if they aren't working correctly you get either a P0325 or P0330 code.

 

[Mr. Toad]

Can you borrow a Scan Gauge or some other real-time OBD II application from someone? Ignition timing is one of the gauges on the Scan Gauge, so you could monitor timing and see if/how much it's really changing when you step on/off the gas.

Not sure what to say on the knock sensors. According the the FSM, they produce a signal under normal operating conditions based on their normal mode vibration frequency and then if they detect engine knock produce a signal that's either higher voltage or a different frequency (FSM doesn't specify which) so that the ECU can retard the timing. Sounds pretty much like if they aren't working correctly you get either a P0325 or P0330 code.

I can check on borrowing a Scan Gauge.

The info in your second paragraph is very helpful. That's more-or-less how I thought the sensor worked, and that's why I can't understand why nothing happens when the pinging is audible. The only thing I can think of is that the sensor's output is not changing in reaction to the knock. Maybe I can confirm this by monitoring the Scan Gauge timing data as I drive and hear the pinging . . .

 

[TrickyT]

...The info in your second paragraph is very helpful. That's more-or-less how I thought the sensor worked, and that's why I can't understand why nothing happens when the pinging is audible. The only thing I can think of is that the sensor's output is not changing in reaction to the knock...

I guess what I was trying to say but didn't say it very well is that I'm not sure that's possible. The sensor is a piezoelectric device and so if it's generating any signal at all (as it does through normal mode vibration), then it must be working okay. If engine knock occurs it affects the sensor's normal mode vibration and the signal changes, which the ECU detects. I don't think there's any way engine knock can be occurring without the sensor picking it up. And if the sensor wasn't working at all you'd get codes. It's pretty much a perfect sensor in this regard.

This is completely off the top of my head, but when's the last time you changed the O2 sensors? I had a pinging problem on my 1989 3FE engine that drove me nuts for months and turned out to be the O2 sensors going bad. No codes, just pinging I couldn't get rid off. Of course this is a different engine with a different ECU than yours, so YMMV.

 

[tacomafj-80]

very intrested of how this turns out. mine has the same symptoms. new plugs, cap, rotor and o2 sensors. timing within specs. dosnt matter what grade of fuel i run, the thing still pings! driving me fn nuts. i was also thinking if water/ methanol injection might help me out, but not sure if its a waste of money on a normally aspirated engine.

 

[Mr. Toad]

I guess what I was trying to say but didn't say it very well is that I'm not sure that's possible. The sensor is a piezoelectric device and so if it's generating any signal at all (as it does through normal mode vibration), then it must be working okay. If engine knock occurs it affects the sensor's normal mode vibration and the signal changes, which the ECU detects. I don't think there's any way engine knock can be occurring without the sensor picking it up. And if the sensor wasn't working at all you'd get codes. It's pretty much a perfect sensor in this regard.

This is completely off the top of my head, but when's the last time you changed the O2 sensors? I had a pinging problem on my 1989 3FE engine that drove me nuts for months and turned out to be the O2 sensors going bad. No codes, just pinging I couldn't get rid off. Of course this is a different engine with a different ECU than yours, so YMMV.

One of the 2 O2 sensors is at least 7 years old. The other was replaced in the last year.

very intrested of how this turns out. mine has the same symptoms. new plugs, cap, rotor and o2 sensors. timing within specs. dosnt matter what grade of fuel i run, the thing still pings! driving me fn nuts. i was also thinking if water/ methanol injection might help me out, but not sure if its a waste of money on a normally aspirated engine.

The only time mine didn't ping was when I used low-octane fuel in Colorado.

 

[longuito]

Hi Mr. Toad and other fellow mudders,

I am having the same exact issues you were having in your original post. Since it's been a while, I was wondering how it ended up being resolved. I have tried the following reocurses without any success (or very little):
1. New plugs (normal heat)
2. Thorough throttle body cleaning and hose inspection
3. Poured 1/3 can of Seafoam into vaccum hose as per instructions
4. Timing adjustment
5. Eliminated my catalytic converter in case it was clogged (not required in my country for vehicles made before 1998)
6. Cleaned injectors with ultrasound and changed rubber gaskets/grommets on the outside
7. Replaced Fuel filter
8. Eliminated EGR system
9. Thoroughly cleaned O2 sensors, becuase mechanic told me that the signal they are emitting is still within spec = no need to change and plus they are very hard to get in my side of the world

Some tidbits of info
A. I always run highest octane fuel
B. My home is way the heck up in the mountains: 2900 meters above sea level, or 9500 ft
C. Engine otherwise in excellent conditions: 124,000 miles, never wheeled by PO, (mall cruiser)

My next steps are changing fuel sock (whenever I can get the replacement), replace knock sensors and o2 sensors. Due to cost and availability issues, I want to avoid changing the sensors if at all possible but that will depend on the feedback I get from MUDDERS.

I have also been considering duing a cylinder head job, but am also reluctant dur to cost issues. Would it be worth only doing a cleaning and changing the seals?

Meanwhile, if anyone has any more useful insight, please let me know, but this is starting to get frustrating ... Regards,

 

[longuito]

Halleluya!

Dear Mudders,

I Just wanted to let you know that my pinging issues have been resolved and were not sensor related, at least not the knock sensor, As is turns out it was a ver simple issue: the districutor gear was off a tooth and no matter how much the baseline timing was adjusted it just was not enough.

So far I have spent well over USD 600 in parts and labor for this, and I already ordered new knock and 02 sensors which are under way. Fortunately for now I don't have to invest in a head job or anuthing like that.

I highly suggest that everyone with a pinging issue make sure that they don;t hve this issue before delving into more serious/expensive work. Regards,