Replaced knock sensor today

[katapaltes]

[Breaking this out from my previous posts on "What have you done to your P5 today?" and creating a new post.]
I finally installed a new knock sensor today. I was previously discouraged due to the amount of stuff in the way from both the top and bottom of the engine bay. Someone here helpfully recommended removing the intake manifold brace (only four bolts), and that helped a lot. I also unplugged the oil pressure sensor (or whatever that single-wire connector is) to keep from accidentally ripping it apart. I just got my oil changed so I didn't remove the oil filter, but that would have helped as well.

As recommended by someone on the forum, I cut off the cable as close as possible to the old knock sensor so that I could slip a socket over the top of it. With the intake manifold brace removed, there was enough room to slip on that 15/16" socket and to pop on a 1/2" ratchet. I may have been able to remove the original knock sensor without sacrificing it, but as I said it's really cramped in there.

I then spun the new sensor on by hand (donated by a very nice former P5'er who had it in inventory) and moderately tightened it up with a crescent wrench. I had to wrench it at an angle, so I had to be careful there. It's an aftermarket part (not a Mitsubishi), but it looked good.

Backing up in time a bit: Before sacrificing the original part, I unplugged the knock sensor and drove it for a day to see if the engine would knock (and it never did). I had wanted to make sure that if I destroyed the original part and couldn't get the new part installed that the car would still run properly. Note 1: With the sensor unplugged, I didn't get a CEL right away, but finally did after minutes/hours had passed. Torque returned the expected P0325 code when I scanned for it. Note 2: I use premium (93 octane) gas because I have A) an MP3 ECU and B) a JDM engine, and the premium gas may have protected me from any knocks while the sensor was unplugged.

With the new sensor installed, the plan is to get cheap gas for the next half tank to see if the engine knocks and report back. The engine certainly knocked previously using cheap gas with the JDM engine and original P5 ECU, but that was with a knock sensor that was completely devoid of its "goo" as you can see in the pics. (The old sensor had drained out almost completely onto the rear of the engine.) Looked like that rooftop bathroom after I got Delhi Belly back in 2015. But I digress...

Pic of old and new sensor. Old sensor has its cable cut and almost no goo left in it.

Here's another pic mainly to show the removed intake manifold brace and the cut cable for the old sensor.

 

[katapaltes]

That was complete speculation on my part.
Our gooey knock sensors may be working just fine, and there is no way of knowing if they are losing accuracy or telling if a new one fixes anything, unless your car is pinging and a new sensor fixes the problem.

You can test your knock sensor to see if it's in range.


View attachment 302248


I remember unplugging my knock sensor and plugging a 550 kilohm resistor into the connector to see what would happen, and I popped the knock sensor code, so the ECU doesn't just look for proper resistance across the sensor and is looking for some kind of signal.

There is still a pretty good chance that you will pop the code if the sensor does possibly start losing accuracy, even if we don't have a "performance code" for our car.


It will be interesting to see what happens with katapaltes's car with a new knock sensor.



I do remember one guy that was having pinging and I mentioned the knock sensor.

I don't think that he had a code but I think a new sensor stopped his pinging.

Above quote excerpted from "What have you done today" mega thread. I put four gallons of 87 octane in my nearly-empty tank today and was able to get the engine to ping audibly, but only just barely.

Below is all from memory and may be wrong. I have a few more variables than most of you what with my JDM replacement engine and MP3 ECU, so YMMV. Incremental changes from previous configuration are in bold. This is all guesswork as I have no formal training and I didn't allow for potential ECU re-learning.

Original USDM FS-DE
Original ECU
87 octane gas
Knock sensor in varying ages of decay over its 19-year lifetime
No audible pinging that I can recall since 2002

Replacement JDM FS-DE in 2020
Original ECU
87 octane gas
Knock sensor goo was by this point almost fully melted
It was pinging

Replacement JDM FS-DE
Original ECU
93 octane gas
Knock sensor still melted of course
No audible pinging

Replacement JDM FS-DE
MP3 ECU (I mean, if I have to pay for 93 octane gas anyway...)
93 octane gas
Knock sensor still melted
No audible pinging

Replacement JDM FS-DE
MP3 ECU
93 octane gas
Knock sensor replaced
No audible pinging

Replacement JDM FS-DE
MP3 ECU
87 octane gas
Knock sensor replaced
Mild audible pinging

So it does seem like replacing my melted knock sensor helped with my engine knock. (After replacing the sensor, my pronounced audible pinging with 87 octane improved to "only" mild audible pinging with 87-88 octane.) If a lot of the goo has melted out of the back of your sensor, you might consider replacing it. Seriously consider replacing any melted knock sensor if you actually hear pinging. You can use premium fuel for troubleshooting.

 

[Buzzman12]

What about running with no knock sensor at all? I've read a few stories on other forums where guys removed the sensor and wrapped it up in a cloth and left it hanging off to the side. That way the sensor "hears" nothing, and won't alter the timing. Is this even feasible?

 

[katapaltes]

That would probably work, but I would not run the car without a knock sensor for long unless you don't care about harming your engine. Knocking is bad for emissions, but it also causes engine damage.

 

[Airsofthawaii]

Good write up, unfortunately I've never seen a stored code for recorded knock events and I think the ecu just uses the knock sensor on the fly if it defects knocking. But yes, at this ago all the goo has oozed out from the stock sensors. I've been running Beck Arnley sensors for a few years with no complaints