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Knock sensor... KILL ME!!!

Kenny_Kline

Well-known member
Put in a brand new knock sensor from the dealer (110% OEM) still getting code 31, knock sensor. Wire color for harness on the main harness is black and white wire with a black stripe. I think this is the right one to be plugger into.

ANy ideas how to make this stupid sensor work correctly? I am about to jump the sensor right to the ECU and see if its a wiring issue.
 

Barnes

Well-known member
Did you over tighten it?
 

1990ggsxnj

Well-known member
Have you logged to see what the sensor is doing?
Are your lifters very noisy?
 
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iLLeffeKt vr-4

Well-known member
Tried disconnecting the battery to reset the ECU?
 

Barnes

Well-known member
lur. Disregard my post. Didn't realize this was a code problem, not a false knock problem.
 

Quoting Kenny_Kline:
ANy ideas how to make this stupid sensor work correctly? I am about to jump the sensor right to the ECU and see if its a wiring issue.



Hmmm...didn't I tell you in another post "The error code for a bad knock sensor is really just a current loop test. It tests to make sure there is continuity in the wiring and sensor. So, the problem has to be with the wiring or a connector, or inside the ECU. But, seeing how it only does it when you are revving the motor, I would bet on a wiring problem." /ubbthreads/images/graemlins/banghead.gif
 

steve

Well-known member
Stuff like this makes people stop trying to help. /ubbthreads/images/graemlins/banghead.gif
 

Kenny_Kline

Well-known member
I jumped the 2 wires back to the ECU and still getting the code after a cleared it. So its either a bad knock sensor or its in the ecu? I dont know how. The ECU was just rebuilt buy a guy here on the forum and also the knok sensor is brand spanking new from JNZtuning and worked fine last year but I will start with swapping the knock sensor out and see what that does.
 

14u2nV

Well-known member
"the knok sensor is brand spanking new from JNZtuning and worked fine last year"

That is contradictory. If it's new, but it's been used, it is not new. If it was damaged during installation or removal at some point [maybe a wired pulled out] then it may be the problem.
 
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What you can do is ohm out a known good sensor, and then compare what you see at the ECU, to see if they match. Its been too long since I measured one, but I seem to recall ~150k. The manual recommends the following tests:

 

Kenny_Kline

Well-known member
Jeff, I tested both connections.

With key ON, car not running, knock sensor disconnected, I am getting 5.74v on one connector and when I test the ground, I get 12.82v when going off the battery.

SO from what you have posted and what I have tested, it seems that the sensor isnt getting a 12v signal as what is required. I will try and jump this wire back to the ECU pin and test this wire again. If its not the wire, its safe to assume maybe a bad ground for the ECU or a bad ECU?
 

Kenny_Kline

Well-known member
Ok so I tested pin 9 at the ecu and get 5.74v. I did this test with both the sensor plugged in and not plugged in. I tested pin 17 & 24 for a ground and both ground are good. Can you think of anything else to check before I swap the ECU?
 

The bias voltage impressed on the knock line is supposed to be 8-11 volts. It seems that I remember 8-9 volts on ones I've tested. It is fed out from pin #1 of the knock board, IC112. If your voltage is low, 5.74 volts when referenced to GROUND, it is most likely a problem with the ECU.
 

Kenny_Kline

Well-known member
Jeff, your speaking another language right now. But from what I have put together, it sounds like I need a new knock board? Is this something you can manage? I can do whatever testing on the board you want to figure out if this is the issue. The ECU was looked over by I think Terry??? He is on this forum and I have one of your chips in it. Not that any of that matters with a failed part in the ECU but just giving you some history.

Is it ok if I pull the covoer off, key on, and test pin #1 on the knock board? I will try to locate the board/pin assuming its numbered when I pull the cover off. If I have to, I will grab a pic. Let me know
 

Kenny_Kline

Well-known member
I found IC112. It has a black circle in the middle of the board. Labeled M67805 ??/ This the right one? If so, what pin do I test?

Also, doing a visual, I found a white powder residue on the ECU cover that goes over the board. hmmmm...
 
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The pins of IC112 are silkscreened onto the board. Pin #1 is the output pin, connected to pin #9 on the back of the ECU. The pin next to pin #1, not labeled, should have ~9.1 volts DC, and pin #1 should be 8 VDC+.
 

Kenny_Kline

Well-known member
Test failed. I am sending to Terry to rebuild. Hopefully, the non eprom ecu I have out of a 1G will have the same knock board and will work.

Thanks for your help Jeff. I appreciate it ALOT!
 
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Yes, all 1990-1994 ECU's use the same knock board, and that's the only place you can get them. I've tried for years to buy them separately, to no avail, which is why I buy bad ECU boards.
 
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