Need some help with a new to me 92 4runner thats not running right, 3.0L v6 and automatic. Issue was known when purchased but still tracing to find the problem. So there is always an extended crank but will start fine every time and will then idle great and drive fine for a bit but then will start to bog down and loose power, pressing the gas will cause back fire/pressure you can hear in intake. First checking the car out there were several random codes which led me to a bad ECU. So upon finding that out I found that the incorrect ECU was installed. I sourced a used one from a facebook forum member and when i plugged it in all the engine lights were gone and it started up so I thought YAY that was is. well drove it a mile or two and still the bogging and stalling happened. Oh and when it starts bogging down I can shift to neutral and turn the key off and restart while still moving and it will run fine again, for a mile or 2 and then same thing again, but it will always restart and run fine????? So now with the correct ECU in it the engine light does come on before it starts bogging down and the only code coming back is code 52 for a knock sensor. The previous owner said he had replaced it already but I went ahead and got another one and replaced the short harness from the main harness to the knock sensor. Now I didn't take the engine apart at this point until I know that is the fix. so I plugged it in and drove it and bam same issue still and code for knock sensor is back again. This is were I am now.

So my thought is that the actual wire from ecu to sensor is bad which isn't hard to believe looking at the state of the wire harness in general. My question is can the knock sensor actually cause the drivability issues I am having or am I just chasing this to still have something else going on? And what type of wire do I need to get to replace that signal wire from the ecu. It seems like it has been an issue but would love a picture of what you have done if any of you have had to make that repair. Thanks for reading my long post and thanks in advance if you can help.

 

Well, it sounds to me like you might have a bad wire going from where the Knock Sensor plugs into the main harness to the ECU. You can start at where the KS's short harness plugs into the harness, and ohm from that plug to the next one. Make sure to flex the harness while doing to ohm check. There should be 1 ohm or less when checking a wire, BTW. Also, check from the far plug you're reading to, to ground. Again, flex the harness. That reading should be infinity.
If everything is good, proceed to measure from the far plug you just checked to, to the next plug. Keep doing this until you either find the trouble, or eliminate this possibility. Remember the carefully check the connection IN the plugs, too. The pins and sockets the go into. Make sure they aren't loose in the plugs, and pushing out when they are plugged in. Ensure there's no corrosion, grease, dirt, etc. in/on them. Clean as required.
Remember, too, that as they age, the insulation on the wire can get old and brittle, cracking easily. This can expose the wires to shorting to nearly anything. Ground, other wires, etc. If there's any question, you'll need to visually inspect the wire's entire length.
Also, the wires and get corroded and fail inside the insulation, with no external signs. This is why the ohm check of the wires is so important. It will find a wire broken inside, or outside, the insulation. Also, this is why it's so important to flex the wires while ohming them. The wire may be broken inside the insulation, but touching until the harness flexes, like when driving.

If you decide to replace the wire, a 14 GA. wire will do the job nicely. The best way to do this is to also replace every terminal and socket along the wire's length.

Does this help at all?
Pat☺

 

I'm not sure I understand what you fix you did. The knock sensor is below the lower intake manifold. So while you don't need to take the engine "apart" to replace the knock sensor pigtail, you sure have to take off a lot of parts (like the fuel rail ...) Some have tried just bolting the (replacement) knock sensor to something like the lifting eye, and while a few claim that it has worked for them, I don't really believe it. The knock sensor is where it is for a reason.

Well, not "ordinary" wire. The knock sensor produces a small signal in a very electrically noisy environment, so it's wired with shielded cable. With plain wire (or even good shielded wire with a disconnected shield), the electrical noise will drown out the signal, and you're back to code 52. You're never going to find "14 GA" shielded wire, but the conductor only has to be big enough to not break (there's only microamps of current). I've never done it, but if I had to I'd start with microphone cable (pretty flexible). You might be able to use RG-59 cable-TV cable out of your dumpster, but that's kinda stiff.

FWIW, the shield is connected to ground near the ECM, but it is NOT connected to anything at the sensor end. I think this is to prevent what audio guys call "ground loops."

 

I didn't "fix" anything per se just got a new sensor and pigtail harness from main harness to knock sensor to test with without spending half a day getting to the sensor since the old owner had already replaced it as well. I am almost positive now that the signal wire from ecu is what is bad. Questions for replacing that: being a shielded wire and grounded at ecu does that mean i just ground the shielding part of the wire? And my pigtail is a two wire to 1 wire into the knock sensor. So to confirm... the brown wire is the shielded wire and I would just replace that one and just re-pin it into the connector??

 

I forgot that knock sensor uses a shielded wire. All it needs to shield the wire properly is to have the shield grounded someplace along it's length. Or either end.
You're 100% correct. Microphone cable would do the job nicely. Even an old computer monitor cable, if it's long enough. Pretty much any shielded cable with a stranded center conductor. A single wire center conductor, like in a TV F type cable, is too prone to break when it's flexed repeatedly, as vehicles do.
I apologize for my error!
Pat☺

 

I finally got some wire to replace the harness. 2 Questions... would you happen to know which pin on the ecu is the correct wire to replace mine is a 92 3.0L with auto? I am not the best with wiring diagnosis. and second the main harness plug has 2 wires that go down to 1 wire thru the jumper wire. Can I just run the new shielded wire straight to the new sensor or do I need to run it to the main connector and thru the jumper that goes down to 1 wire? Thanks for your help I really want to get this thing running right

 

I still don't understand what you did. The "pigtail" connects directly to the knock sensor. To replace the pigtail, you have to get TO the knock sensor, under the lower intake manifold. So it sounds like you have the replacement, but you have NOT installed it, as that's a pretty big job. Correct?

If you haven't replaced the pigtail, what makes you think you have a problem in the engine harness?

 

I have a new sensor and a new pigtale harness I plugged the new pigtale into the main harness and a brand new knock sensor. "for testing purposes" this should be enough to show the computer that there is a good sensor. the code is still there and the wiring harness looks like someone blind and in the dark tried to make repairs so I am nearly 100% sure that is where the issue is I am just trying to get info on which pin to reroute the new wire and if i can completely bypass the connection from main harness to pigtale or does it have to stay.

 

Do you know for certain that the old owner used a OEM toyota knock sensor and not a 10 dollar ebay one...cause ebay sensors dont work,

 

** Update ** I ran a new wire from ecu to knock sensor and now no more knock sensor code. test drove it and the stalling issue is still happening only now there is no engine light to chase... I checked the TPS and it was not the resistance was off and could not get it in spec, it looked original so I ordered a new one from toyota got it today and went thru the resistance checks for setting it up and all was in spec. I got everything back together and still it is stalling but will reset and run fine as soon as I turn the key off and restart while still rolling down the road. Looking it over further even though the idle is right I cant see the timing mark on the crank when trying to set the timing? I moved the distributer the full range of adjustment and dont see it. I was able to see the time marks before doing anything with the TPS? could that have affected the timing that much or am i missing something else?

 

Just realized I never posted the fix for this issue. After all I went thru i decided to drop the tank to check all the connections and hoses and found the previous owner had replaced the fuel pump and when he did he broke one of the metal hose connections on the housing. After doing so he just clamped a new hose to what was left of the connector but he didn't get enough hose and it was kinked. This was the fuel return hose and since fuel wasn't getting back in the tank it just backed up into the engine basically flooding it and causing it to stall. So attached a longer fuel hose and bam no more stalling.

 

Better late than never glad you got it sorted!!!!