I've had my 91 4runner for a year or so now. It has the 3vze, 5 speed and is four wheel drive. I bought it knowing it needed a head gasket. I replaced both head gaskets, timing belt, idlers and tensioner, knock sensor and harness, all top end gaskets, water pump and radiator. After firing it up I had a few codes. Had 12, 24, 31, and 52. I managed to repair all but 52.

I checked continuity from the ecm to the harness and all is good. I ran a shielded wire straight from he ecm to the knock sensor harness just in case and did not fix the issue. I need to try to pinpoint the issue. Engine is running good but as soon as that code comes up it turns into a dog. Not to mention I'm in comifornia and it won't pass smog with the light on.

I have read about moving the sensor to the engine hook and wouldn't mind that at all if it will fix the problem.

I'm wondering what if I were to ground a wire to the block and wrap it around the sensor giving it ground, then run a wire from the sensor to the harness so the sensor isn't connected to the motor other than its ground. If the code is still coming up wouldn't that point to the ecm as the issue since there's no way the sensor can sense knock or ping if it's not screwed into the block?

If this sounds desperate it's because I am. I really want my shooting rig up and running, and I'm really tired of slicing my hands up on this motor. Eventually I'd like a 3.4 swap but that's not I'm the budget right now.

I'd appreciate any help you can offer guys. I've searched the web and checked everything I can find and nothing is working.

 

Just what brand knock sensor??

The connection where it plugs into the harness is clean??

The threads in the block are clean giving it a good ground??

It comes down to the sensor the wiring and connections or the ecu/ecm a pretty simple circuit

I have had connections that tested good with a meter plug it all back together and it does not work

 

When you refer to the knock sensor harness, I assume you're talking about what is often called the "pigtail," the wire from the sensor under the intake manifold to another connector. That's the component that most often fails; if you didn't replace it you need to. Checking continuity is where I'd start, and after what you've done I'd be tempted to check continuity all the way from the ECM to the sensor, through the "pigtail" connector. Remember that the ground of the shield is only connected to ground at the ECM; not at the sensor, and not at the pigtail connection. The ground (as you already figured out) is important, so do visually check the wiring to see if there is a worn spot that might be shorting the ground to anything that generates electrical noise (e.g., any ignition component).

I've read it about it too, but I just can't believe it would work. (As many people report it does not work as those who hint that it might.) Toyota wouldn't put the sensor in such a difficult location if it would work okay out in the open.
Remember that code 52 doesn't mean that the sensor is sensing knock. Instead, it means that the ECM "hasn't heard from the sensor" in a while. So if you wired up a sensor and held it in your hand, you'd still get code 52 because the ECM isn't sensing the correct engine signal no matter where the ECM sets the timing.

 

Purchased sensor and pigtail from toyota dealer, clean connection, clean threads.

 

Pigtail was replaced with the sensor. I thought it sounded hokey too but at this point I'm willing to try anything.

That's makes sense. Since I've check continuity and put in a new wire between the pigtail and ecm maybe it's the ground wire I'm having an issue with. I haven't been able to find any info on the ground, is it a common ground with other sensors or it's own? Any idea what connector and pin on the ecm it is?

Thanks for the help!

 

This may not help. My diagrams show the shields (knock, 1 or 2 O2 sensors, distributor) all come together at splice I1, shown to be right next to the 3 ECM connectors. Then it's off to splice E9 in the engine wire under the hood (where it joins with almost all the other grounds to the ECM), then to the camshaft ground point on the engine.

Good luck, and let us know what you find.

 

Looking at my 1992 4Runner EWD the knock sensor grounds to the block .Having only one wire in the pigtail plug.

Since I don`t have a 3.0 I can`t do a visual

So if the ground is poor from the block to battery that could be a problem.

 

The ground of the sensor itself is to the block (through the threaded connection.) The pigtail should be shielded, but does not connect to the block ground at the sensor. So there is a single-pin plug to the sensor, but a double pin plug between the pigtail and the rest of the harness.

The reason for grounded-only-at-the-ecm is to prevent what audio engineers call "ground loops."

 

Thanks for the info guys, hopefully will get to work on it soon.

 

Check the link in my signature, it may help.

As usual, scope103's got it down.

 

I have a 95 4 runner 3.0, code 52. I rebuilt the whole engine now the thing trows a code 52. I replaced the sensor and pigtail. I cleaned the connections and even ran a shielded coax cable. I still have the same problem. I didn't use the ground at the pigtail ie; cut and ground to the coax. I used the one to the sensor. I did however use a gasket between the sensor and the block. Do I need to run the ground from the pigtail to the coax or did I mess up using a gasket. I can't seem to figure it out myself.

 

I doubt the gasket matters; the sensor will ground to the block through the threads.

If I understand your post correctly, you used a factory pigtail, but replaced the pigtail-to-ecm harness with coax. Then, rather than run the ground through the harness/pigtail connector, you left that open and connected the pigtail ground to the sensor. How did you do that? The connector to the sensor has a single pin. Or did you make up your own pigtail?

Use your multimeter to check for continuity from the sensor end of the pigtail all the way to the ecm. Check to make sure there is NO continuity from the shield (or any other ground) to that conductor. And, if all else fails, I would suggest wiring it as it came from the factory; continuous shield from the sensor to the ecm, but connected to ground only at the ecm.

 

I used a factory pigtail, but unsure if the sensor was factory. I had trouble with it throwing the code. I read on this form about changing the wire and using a sheilded wire. I did that. I run the sheilded wire from the end of the pigtail using the connector already in the main wiring harness. I cut the wire from the ecm at the harness conector and soldered the conection (Black wire) the used heat shrink tubing to cover the conection at the plug in and at the ecm. I grounded the sheild on the wire to the ecm. I did not solder the brown wire at the plugin to the sheild. I will check the wire with a multimeter later on today when I get time. The coax did a great job but I must have missed something along the way. I'm rushed for time right now, I will check the form latter this morning.