1991 4Runner Knock sensor code issue!

DOO · 07-23-2014, 12:00 PM

I have a 1991 4Runner that I picked up from a friend that had a knock sensor code so I replaced the sensor and pig tail to it. After it was replaced I timed it and took it for a test run and seemed to be running fine. Then after about a mile the check engine light came back on and started to run a little rough but not as bad as before I changed knock sensor. I checked the code and it threw code 52(knock sensor/ecm) and 43(ignition/ecm). I cleared the codes and now it only threw 52. This is not the original engine and I am not sure what year it is but does appear to be at least 1989 to 1991. I was wondering if anyone can give me any ideas on which direction to go to figure out what might be the cause. The only thing I can think of would be the ECM and not sure how to check that out. Over all this vehicle is in pretty good shape and I don't want go thru the hassle of finding a different one so please give me some ideas.

Brian R. · 07-23-2014, 01:38 PM

Your problem is probably in the knock sensor circuit. Check all the connections and wiring.

Any more detail will require knowing what engine you have.

DOO · 07-23-2014, 07:35 PM

It is the 3.0 V6 and I have replaced the knock sensor and the pig tail, both new. Did the self diagnosis with the on board diagnosis port by doing the recommended jumping of two ports. I don't know if there is something else that may cause the same code other than the ECM having problems.

Brian R. · 07-23-2014, 09:56 PM

How much of the wiring between the ECM and the knock sensor did you test? If there is a break or short in the wire somewhere, it is likely the problem. Saying you replaced the pigtail doesn't tell me enough to judge over the internet...

If you haven't, test the whole circuit.

Here is a link to a '93 Pick-up FSM which has your engine in it. You may have to login to the site to download.

http://dc526.4shared.com/download/Ym...38b3&lgfp=2000

DOO · 07-23-2014, 10:40 PM

I will do some testing of the wires and let you know what I come with. I won't be able to get to it next week and I will check that site.

DOO · 08-03-2014, 10:09 AM

Well I have tested the wire and the main wire is good but I believe I have found the issue. As you may know that it is a shielded wire and on the side of the wiring that comes from harness and just before the connector to the pigtail the factory tape was brittle and the insulation for about 1/4 inch has exposed the shielding wire and it has frayed. I was able to talk with a mechanic at the Toyota dealership. So this is what he told me, I can fix it and if were a newer vehicle I wouldn't be able to. As long as the wire's are touching and making contact it should work. I have tried to stripe back the insulation and pull them together the shield wire and tape it back up but with no luck, still got the same trouble code and I did clear it before starting the 4R. I tried to use a piece of foil to help make contact. I think that was not such a good idea, so I am going to try again and come up with a different way to wrap the wire maybe with a small wire and wrap it with a thin wire that I have. Other wise I may just figure a way to adapt to the connector and connect to pigtail and run a new wire then splice into the old wire near the ECM. If anyone has any idea's on repairing this please chime in. Sorry I didn't have a picture to show you but I will see if I can throw one on here.

Brian R. · 08-03-2014, 09:42 PM

If the shielding is making contact with both sides, then it should be good, but stranger things have happened.

IF you haven't already done so, make sure the sensor connector is clean/oil-free and making good electrical contact with the sensor.

DOO · 08-04-2014, 09:15 AM

The contacts were clean on the pigtail and sensor but I did notice that the contacts on the connector from the harness were a little green so I am going to try to clean them the best I can. Now the shielding should be grounded at both ends, am I correct on that? If so, I can't find the the grounding on the other end of wire or does it just ground at the sensor?

Brian R. · 08-04-2014, 11:10 AM

I believe it only has to ground at one end. At least that is my limited experience with other circuits.

DOO · 08-17-2014, 11:58 AM

Well this is where I am at. I found a wire harness at a salvage yard and it had the wire I needed and I pulled it and it is in great shape. I plugged it in to the pig tail and tapped into the harness down by the ECM. The shield is tapped into where the other KS wires shield connected to the harness with some other shielded wires came together. I did test the new wire and it was good so I started it up and double check the timing and it is still good. There is a miss that I can hear. I drove it down the road and made it just over a half mile and the check engine light came on. It was the same code. The miss was there before the light came on. I believe there is something else at this point that is throwing the code. I don't hear a knock, it is for sure, to me, a miss. A friend at work thinks it could possibly be a dead cylinder. Anyone have any other idea's?

Brian R. · 08-18-2014, 02:25 AM

Miss is most likely electrical. Check the spark plug circuits, including the plugs. Do a compression check. Clean your injectors - maybe first try a can of some fuel treatment/injector cleaner.

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