PyroJim

OK, I'll keep this short. This topic has been discussed 100 times elsewhere. I challenge anyone to solve this or to have a worse story!

It's been almost two years that we've been screwing with a "52" knock sensor code on our 1990 4 Runner. We have done the following:

1) New knock sensor - twice.
2) New knock sensor pigtail
3) New coax wire to bypass the factory wire
4) Replaced ECU with used ECU.
5) Replaced engine with 1995 engine.

The code 52 persists. The expense and time spent has been enough to have bought a new car by now. We've tried everything already suggested including externally mounting the knock sensor outside of the motor.

Does anyone have any suggestions? The next step is to have the ECM checked, but we honestly thought that it would be pretty rare to have had two bad ECMs that both just happened to fail with a 52 trouble code so we doubt that it is the ECM, but who knows?

Anyone have any better ideas? The next noise you hear may be us blowing this car up.

PyroJim

Punchy

Just for S&G, You can create a bung that you can screw into one of the bolt holes on the passenger side motor mount holes or other holes on the block.
Temporarely of course.


I would still say its the coax from the pigtail to the ECU connector and not grounding the shielding correctly.


If the shielding is not grounded well the center lead will pick up the RF (injector and IGN signal) noise in the harness.
Also make sure you have a good engine to body groundstrap.

scope103

You've got a replacement engine, a new knock sensor, a new pigtail, a replacement ECU ...

and a homemade coax wire from the pigtail to the ECU.

I would concentrate on the most likely to not work component, which to me sounds like the pigtail-ecu connection. Have you verified that there is continuity from the terminal on the ECU to (at least) the center-pin of the pigtail connector? Have you verified that there is continuity from a ground pin of the ECU to the other pin (shield) of the connector? Do you have the ground/shield connected to ground at both ends? (You shouldn't; the shield grounds only at the ECU. I think this is to prevent what audio types call "ground loops.")

PyroJim

We tried the trick with running the sensor on top of the motor. No change.

You're suggestion makes more sense than a second bad ECU. The new shielded wire is actually 2 conductor shielded audio wire connected to the knock sensor harness at the motor - two conductors, one goes to the shield on the factory harness and the other goes to the "hot" lead on the knock sensor. We duplicated the factory grounding design when we used the new wire. I could try an RF type coax, but the cable that I used is pretty heavily shielded, so I'm not sure that an RF coax would offer me any better RFI protection. I could also try adding an additional ground connection at the splice point on the top of the motor.

The Check Engine light does not come on right away. The car can idle forever, or even can take a few gradual throttle applications. If you stab the throttle and race the motor up, the check engine (code 52) pops up almost every time.

I'll look into your suggestions. Thanks for the input.

PyroJim

Continuity on both conductors is good.
The "new" shielded wire is grounded at both ends. The knock sensor has a 2 pole connector. One pole is the "hot" lead and the other is the "ground" The sensor takes one of those terminals to engine ground by way of the sensor being threaded into the block. There is no secondary ground at the engine beyond the sensor itself. The shield of the shielded cable is then tied to one of the ground wires at the ECU.

I wonder if I could "super shield" the shielded cable by wrapping the cable in something additional.

PyroJim

By the way, the motor came out of a 1995, and was running fine and was NOT throwing any codes while it was in the 1995.

This has to be a wiring /ECU issue. Or so I'd like to believe.

scope103

The (stock) knock sensor on my '94 has a single conductor. The wiring diagrams are clear that the shield is NOT connected - to anything - at the engine end. The pigtail has two conductors (signal and shield), so it has two conductors at the ECU end but only one at the sensor itself.

So, did you get a Toyota knock sensor with a two-pin connector, AND a Toyota pig-tail to match? If so, something has changed since my truck was built (imagine that -- something changed in the last 20 years!) But if you had to make-up a way to connect the ground at the engine end, I would be concerned about that.

Gevo

When I went to the dealer and purchased my pigtail, it was NOT the same one as the one on the car and it did NOT fit on my single lead knock sensor. The parts guys were very confused, because the VIN and PN matched... anyway... The solution to my code 52 is outlined in this thread (starts at post #217 -->>> https://www.yotatech.com/forums/f199...5/index11.html

NOTE:: The grounding was my final code 52 problem. Check your grounds. I started checking resistance from my battery terminal to all other ground points and was completely shocked at how many ground points were reading above 1ohm. Anythign above one ohm I set out to fix. Especially the circuit that the knock sensor shield connects to (E2) . Also, the thread I linked above, I noted which wires I used before the code 52 went away. I tried audio wires, didn't work.

PyroJim

We will look at using a different type of shielded wire today - also we'll go crazy on grounding.

Our stock knock sensor wire is most definitely two pole, and the wiring diagram for both the 90 and the 95 motors show it being grounded at the engine end.

I think we are close. Once we replace the wire (again) we'll see what happens.

Gevo

I have been using the wiring diagram for the 1995 ( I believe) on my 1991. http://snjschmidt.com/wiring/Engine_Control_3vze_3.jpg

The wiring diagram shows some connection on the other end of the knock sensor, but trust me it is not suppose to be grounded AT the knock sensor.. This is about the shielding wire. As Scope mentioned above, this causes the ground loop affect and the electrical noise gets bounced around in the shielding wire instead of draining on one end to the E1 ground.

But, you can try it both ways and see what happens, it did not work for my 1991 style knock sensor. But if your knock sensor has two connectors, I imagine one of the is a on-grounded shielding wire connector that juts plugs into the harness.

PyroJim

The current knock sensor is the same one that came with the engine. It was working fine when we pulled the engine out of the 95. Logic would tell us that it is the wiring or the ECU.

Gevo

Yes, agreed. What I am talking about is all between your knock sensor and ECU.

Tennesseestorm

I don't have much info to offer, but my dad just had a time with his '94. He had the code 52 and after replacing this and that, he finally got it running good. I think he had to not only replace the knock sensor, but several others as well.

Good luck!

PyroJim

Ok, here's the latest on the Knock Sensor from Hell:

1) We double checked ground connections. We added additional grounding/bonding straps just for fun. This sucker is grounded. This made no difference whatsoever.
2)Researched the grounding at the knock sensor issue. Gevo and Scope you were correct. It as absolutely NOT grounded at the sensor. The pig tail is two pole and reduces to one pole right before the sensor connects to a one pole plug. The shield is just flying and taped/heat shrunk at the factory. I stand corrected.
3) Tried mounting the knock sensor outside of the engine again. Same result. Check Engine. Code 52.
4) My son did some more Googling and found a guy somewhere with a similar problem with a knock sensor on a Honda. The Honda guy solved it by buying a piezo transducer at Radio Shack (part #273-0073) and installing it in place of the knock sensor. I'll be damned if it didn't work! No more "check engine" light, no more code 52.

I understand that we currently do not have any anti-knock protection, but on the flip side, we also do not have a check-engine light and we can get the stupid thing smogged.

It only took two years. Technically, we still have not solved the problem, but we have treated the symptom and for the time being we're calling it a victory. I'm hoping that the check engine light stays off long enough to just get past the smog test.

What a PIA.

Gevo

INteresting to see the piezoelectric device work.. kinda fun!

Are you still using the shielded audio cable? During my own hellish code 52 issues I read some people use it with success, and some no success.. I was the latter.

Well, hope that works long enough for you, but from what I understand.. the engine uses the knock sensor input to adjust the timing all the time, so in the long term you may be damaging your engine.

scope103

Wow.

While this is far outside of my experience, my suspicion is that you DO have "knock protection." Code 52 is saying "I haven't heard from the knock sensor." Now, apparently, your ECU is satisfied with what it is hearing from your Radio Shack device.

The real advantage of getting rid of code 52 is timing; when the ECU loses the sensor, it dramatically retards the timing to save the engine. Meaning: it runs like poop. I am hopeful that your sensor will work well enough to tell the ECU "hey, back it off" as the ECU advances the timing.

PyroJim

We are still using the same shielded audio wire. It is basically a heavy duty microphone cable, with a very heavy shield and we are using both of the two inner conductors as one conductor, with the shield connected to the pigtail connecter upstream from the sensor and to groud at the ECU. We live in a remote area and the only local source for RF coax was Radio Shack which wanted 20 bucks for a piece of RG-59 with a couple of connectors on it. I couldn't see paying 20 bucks for 6 feet of coax, so I'll defer the new coax until I get to a store where I can purchase it reasonably.

I doubt that the piezo is doing much more than satisfying some electrical variable that the computer wants to see. I don't think it is transferring any knock data. It IS however keeping that DAMN CHECK ENGINE light off for the time being, and that will help us get it smogged, I hope.

Ironic that after thousands of dollars and probably hundreds of hours of work, it all comes down to a $2.00 Radio Shack part to get us on the road.

I will continue to work on the base problem, but only after I get the smog passed and get this thing street legal (more or less) again.

PyroJim

The truck passed the Californian Smog test today. I am amazed. We still need to figure out the root cause, but having the ECU happy with this 2 dollar piezo item blows my mind. It almost means that the ECU is working properly. So - we have won the war, but lost the battle? I'm still at a loss as to where to look next. The piezo works fine with the shielded audio wire, but the factory knock sensor does not! The factory knock sensor worked fine when the motor was in the other car, but it does not seem to work in the 1990.
Does anyone know if a 1995 knock sensor is any different than a 1990 knock sensor? Maybe that's it. Maybe the 1995 engine's knock sensor is not compatible with the 1990 ECU? I have no idea at this point.

Gevo

At your expense i know.. but this is very interesting to me! Its hard to say if the electrical properties are different from 2990 to 1995, but some change was made to the knock sensor for models from 1991 august and newer.

If you looked at my solution youd see that the knock sensor mounted to the drivers side hanger is working fine with the shielded wire i purchased. I cant imagine if you replicate what i have that it wont work. Mine has been working fine on the hanger for a while noe. I even tested it by advancing timing up until it registered a knoc, code 51 if i am remembering correctly. So its giving the ecu somewhat of a decent signal. That put my mind to ease a bit.

zombie_stomp

I'm not an expert on fuel injection systems, but I have become aware that the knock sensor provides information to the computer, along with infor provided by other sensors, how to adjust fuel delivery and timing advance/retard. If not much else changes, it runs as it did from day one. Then if something changes, like air flow or fuel quality, it helps dial it in for you.

So while it delivered a signal that the knock sensor was not providing any info, I wonder how it was running. I know my post may not be of any additional help- I tried reading it all he other night, and I know you have done completely exhaustive service to try to get the code gone. But if the code and check engine light was the only trouble- and I know many states including mine do not pass emission even if only the check engine light is on- then maybe you have found the loophole you needed just to pass. If so, maybe the only things to do are to either have a bypass switch that lets you switch between the knock sensor and your piezo gadget, or try that 1995 ECU, as you said.

I hope one of those options works out long-term. If it ran and continues to run fine with the piezo deal- or with the check engine light on anyway, at least you have the option while the smog testers are not watching.