This is a 93 and it's getting codes 25 and 52. Just found this unplugged connector. Could this be why?

 

What color are the wires going to it?

 

Black and brown.

 

Sounds like the knock sensor to me. That would explain the code 52 (no signal from knock sensor), anyway. Don't know if that could confuse the ECU enough to also cause the code 25 (too lean condition).

 

The knock sensor has a single black wire attached to the connector.

I looked at the wiring diagram and I can't find anything that has those color wires going to it.

 

My wiring diagram shows a black wire going to the knock sensor itself, and a brown wire connected to the associated shield.

(Hopefully this diagram attached)

 

Curious. Here is another one.



Alternatively, IIRC the knock sensor wire sneaks up through a small groove between the head and manifold. Nowhere to be found on this truck but the rubber insulator is still there:

 

The brown wire is attached to the shield with a splice, not a connector. That octagon with the "E27" shows you that it is a splice located in the engine compartment. Further down you will see an octagon with a "I15" in it. This splice is located in the Interior.

When a wire is attached to a connector, it will have a small number signifying what pin on the connector the wire is located on. Pin #1 in this case.

I just looked at my spare '94 22re harness and it indeed had a single black wire going to the knock sensor connector.

 

So are you saying this isn't the connector for the knock sensor?

 

You obviously have more experience reading these diagrams than I do. Thanks for explaining the rationale behind some of the labeling and numbering.

 

Actually, it almost is. (Thanks to RJR, who got my eyes looking where they needed to be) That is a connector, that connects to another wire, that then connects to the knock sensor. If you look at the diagram that RJR posted, you will see two rectangles that have "ED1" in them. (rectangles signify wire to wire connectors) That is the connector you are looking at. There is then another wire that attaches to the "ED1" connector and then goes to the knock sensor. The splice is located in this intermediate wire.

The intermediate wire that needs to hook your connector to the knock sensor looks like this...



My 22re does not have this intermediate wire. That is what threw me off.

 

Well thank you guys. Looks like the manifolds are coming off. Or can this little sensor be bypassed? The truck runs like poo so I've gotta Do something. Do you think the code 25 might originate from this as well?

 

No, you really have to fix this. The engine runs most efficiently when the timing is advanced as far as possible. However, advancing it too far will result in knocking and subsequent engine damage (holes in pistons, stuff like that.) The knock sensor tells the ECU how far it can go without damage occurring. If the signal from the knock sensor is missing, the ECU is "flying blind" , so it throws code 52 and retards the timing a lot to stay well away from the knock zone to avoid catastrophic damage. This results in an engine with poor power and fuel economy, as you are experiencing.

Before electronic controls, engine timing advance was handled by centrifugal and vacuum advance mechanisms in the distributor. These mechanisms essentially don't exist in the Toyota distributor, so there is no way to get the engine to run well in the absence of a working knock sensor.

I don't know if the code 25 could be a collateral result of your disconnected knock sensor. I would fix the KS first, reset the codes (pull the EFI fuse for 30 seconds) and see what happens.

 

The intake manifold has to come off to access the knock sensor. (The wire between ED1 and the knock sensor is often called the "pigtail.") The knock sensor can't be bypassed. Occasionally, someone suggests mounting a knock sensor to the engine lifting hook to overcome the code. I really don't believe this could possibly work, but if someone claims that it worked for them, I can't dispute the claim.

The truck runs like poo because code 52 dramatically retards the timing (to save the engine). Yeah, you gotta fix it.

It's hard for me to imagine the connection to code 25, but with the timing off that far lots of things could happen.

 

Thank you for the insightful replies. Very good information. This truck needs head gaskets too so I'll sort that out when I'm down to the bare block. Thanks again.

 

Any chance a prolonged code 52 would cause overheating?

 

I fought code 52 for quite a while and never had overheating problems. I don't see how it would cause that kind of problem.......

 

Yeah, I figured. Just don't want to pull the heads yet.

 

code 52 will not likely cause overheating. You will be running very rich, NOT lean, however, you could plug up your cat from running that rich for a while, and THAT could cause over heating. That being said... I ran with the code 52 for a year and a half before I got it sorted out, and never had any issues.
You can get away with mounting the KS on the engine lifting hook, BUT... you will only be sensing knock from half the engine. the engineers at Toyota mounted in the valley for a reason.....