Knock Sensor help please

[ariff]

So on the way to work this morning, my CEL came on and I pulled the code in the parking lot and I am getting a knock sensor error 52 front sensor. I spent the night in the garage troubleshooting this evening and I am a bit stumped. Hopefully, others may have some ideas for me to try. So far this is what I have done:
1. Removed the sensor and tested per FSM there is no continuity between the case and the terminal.
2. Reinstalled the sensor and tested it with my meter. Knock sensor terminal to the positive lead of the meter then black lead to batt ground. Set to lowest AC voltage settings and knocked on the block by the sensor. I am seeing voltage when doing this. So this tells me the sensor seems to be working. I also did this test on the rear and it gave me the same voltage settings.
3. Checked the connector for any exposed wire, cleaned them well and applied some dielectric grease to the connector.
4. Filled up with premium gas ughh
5. Swapped out the ecu (I have one from a 94 in there currently) with my old ECU.
6. Checked timing and it is set to 4-5 degrees.

After doing all this stuff I am still getting the 52 error. I saw some posts about the EGR having an impact on this. I have deleted my EGR and all VSVs a few years ago. My wires by the EGR are all in good shape. My next step is to swap the rear and the front and see if the error moves to the rear position. Not looking forward to trying to get that rear one out, so if anyone has any other ideas I am all ears. I hate replacing parts if they are not bad and this one appears good. I did look at the schematic that I am guessing shows where the knock sensor terminated into the ECU. I wanted to check for continuity from the knock sensor connector to the ECU. But I could not figure out which wire to test. I tested all of them and got continuity on several of the wires so I gave up there. Does anyone know how to read this? I was guessing that is connector C which I have no idea which one that is. Thanks!

 

[ppc]

Sensor #1 would be connector C = E9 pin 6 on the ECU. Kind of mirror image to connector because you are looking at the ECM not the wiring harness. The pins are numbered top row right #1, bottom right #9. Connector A is on the right and D on the left in the image below. This was found on page 233 in my 94 manual. It is in the first few pages of Engine - SFI System section of the FSM.

 

[ariff]

Thanks again Phil.. I only have the pdf version of the fsm and sometimes using it is a bit difficult trying to find stuff. I need to look into getting a hard copy. I think it would make my life easier. I'll test these out and report my findings..

 

[ariff]

Ok so I just checked continuity on the knk1 terminal at the ecu and I do have continuity so that tells me that the wire appears to be ok. Anyone else have any ideas on what to check?

 

[baldilocks]

I’m curious what will happen when you swap sensor locations.

 

[ariff]

Yeah I guess that's my next option.. I'll be sure to post back what happens.. Could there actually be a knock in my engine and this means the sensor is working as designed? I would think if this were the case both sensors would pick it up and I'd hear it. I hear no pinging or anything like that. I don't notice any loss of power or any noises. If my CEL was not on I'd think everything is running just fine.. I have a medical condition known as CEL OCD.. I can't stand driving a vehicle with the CEL on makes me crazy, how people can do that for months or years boggles my mind ;>)

 

[baldilocks]

I believe that the sensors work transparently to retard timing if necessary and the diagnostic trouble codes are to alert us of a problem with the system. This is my take on it anyway.

 

[ppc]

Yeah I guess that's my next option.. I'll be sure to post back what happens.. Could there actually be a knock in my engine and this means the sensor is working as designed? I would think if this were the case both sensors would pick it up and I'd hear it. I hear no pinging or anything like that. I don't notice any loss of power or any noises. If my CEL was not on I'd think everything is running just fine.. I have a medical condition known as CEL OCD.. I can't stand driving a vehicle with the CEL on makes me crazy, how people can do that for months or years boggles my mind ;>)

In the other thread you started I posted an image from the FSM of the fault codes. One of the columns is "diagnosis" which defines what raises the fault.

For the benefit of others searching the forum in the future please don't start multiple threads related to the same problem.

 

[ariff]

In the other thread you started I posted an image from the FSM of the fault codes. One of the columns is "diagnosis" which defines what raises the fault.

For the benefit of others searching the forum in the future please don't start multiple threads related to the same problem.
[/QUOTE
Will do thanks!

 

[ariff]

OK well I went out and swapped the front sensor to the rear and moved the rear one to the front. Took it for a drive and within 5min I got the CEL.. Checked the code and it is reporting 52 again front sensor.. so it does not appear to be a sensor issue. I was hoping it would have moved the problem to the rear then easy fix, replace the sensor.. Trying to think of anything I may have done leading to this issue. I changed the oil and cleaned\greased my engine grounds and battery terminals. I have Tripple checked all the grounds I cleaned and they are all tight and good. I cleaned up some of my oil leaks with some degreaser and a rag when doing the oil change like I do on every change.. I can't imagine these things would have caused this problem. I am guessing it is just bad timing I started getting the knock sensor error after I did some maintenance. Running out of ideas now.. I also set my timing to the factory spec of 3 degrees still no luck.

 

[baldilocks]

Have you verified continuity to the ecu yet? Sounds like you need to have a hard copy of the fsm shipped in. You should be able to find one on eBay, that’s where I got mine a few years ago.

 

[ariff]

Have you verified continuity to the ecu yet? Sounds like you need to have a hard copy of the fsm shipped in. You should be able to find one on eBay, that’s where I got mine a few years ago.

Yeah I did reply with that info earlier this morning.. I have verified I have continuity to both front and rear knock sensors at the ECU. So wiring appears to me good going to ECU.. Yeah I just have the PDF version of the FSM which works fine, but makes it hard to find things sometimes. A hard copy would defiantly be better..

 

[ariff]

I am wondering if somehow I could monitor voltages going to the ECU for the knock sensor with my Digital meter? I have no idea what I would be looking for but I'd think there is some way to monitor that sensor in real time? I wish I had one of those OBD1 readers..

 

[ariff]

Ok I think I may have found the issue. Not sure why I did not test this first. If I place my meter in the knock sensor connector and the other lead to ground I get continuity. I don't think this is supposed to happen. Somehow it is shorted to ground. Now to figure out why..

 

[baldilocks]

Following

 

[ariff]

OK I am happy to say I finally figured it out.. Took her for a nice 15-20 min drive on the highway and no more CEL's yeah! It is always such a good feeling when you finally figure out a tough problem. Turns out the knock sensor wire had cracked just enough to short out on a few of the shielding strands maybe 6-8 inches or so into the harness. Once I unwrapped the harness I noticed that every wire was cracked in the exact same place. Right under the tape that Toyota used on each connector wire. It is hard to explain but if you ever get in there you'll see what I am talking about. It was grey and had become very hard over the years. I removed all this tape cut off all the bad connectors and re-soldered and weatherproof shrink wrapped them. I know some folks say not to use solder when repairing wires. I have made these kinds of repairs for over 20 years on cars and never had one fail on me. However, I have had the butt connectors fail. So I stick to what has worked best for me. I was able to make all the repairs from the driver side wheel well right above the starter. Here is a pic of the mess I started with.

Hopefully this will help someone else out in the future. Thanks so much everyone for all your assistance along the way.. We have a great commuinity here on mud.. Have a good week!