2.5 knock sensor

[WoodsWagon]

My 1998 legacy outback is throwing a code for knock sensor circuit malfunction and pulling all the timing. It's at 0degs advanced when it's under load= gutless.

 

I tested the knock sensor, right resistance, and if you hook it up to the O-scope, it makes a nice voltage spike when you rap it.

 

The wiring seems OK, I haven't been able to test between the connector and the PCM. Anyone have a connector view for the 2.5l PCM? I know it's a white wire going into the PCM, but there's more than one white wire.

 

The engine is also misfiring bad. It snapped out of it once, ran perfect, advanced timing, and didn't misfire, and then went back to running bad.

 

I just resealed the engine and installed a new timing belt. The marks are lined up, I checked 3 times, and my dad checked once, they're dead on.

 

The Idle air control motor is sticking. When you start it, it goes to 2k rpm, then does a sudden jump to 1k where it will idle. If you put it in drive or kick the A/C on, it almost stalls. I think it's just gunk built up in it, so I'm going to use carb cleaner to try and free it.

 

I've got untill tomorrow morning to get it running right for it's salvage inspection. I'm also taking college finals at the same time, so the pressure's on.

[Tech1967]

If there's nothing for it to detect (knocking) and the code still sets just replace the sensor. Bad ones can still have good resistance and spike when you test it. Generally the problem is that they throw noise when they shouldn't and set the code.

[WoodsWagon]

I think the piston slap was tripping it off. I relocated the knock sensor to the bracket where the main ground strap goes, and the code dissapeared. Totally defeats the purpose of the sensor, but what the heck.

 

Used an IAC off of a junk EJ22 I had kicking around, that solved the idle.

 

Replace all the plug wires, that cured the misfire. It's running pretty strong right now. I still have to change the tranny and rear end fluid, swap a tie rod, and put a split flange on the exhaust right behind the cat.

[porcupine73]

Wow sounds like you're 3 for 3 on solving the problems which is a lot better than I usually end up with on my sub...

[nipper]

You do know the knock sensor is a pizeo electric device. It generates a small ac current that the ECU reads. Just because you tap it and it reacts doesnt mean it is funtioning properly.

This is one of the fault codes that when it says bad knock sensor, it is a bad knock sensor.

 

nipper

[WoodsWagon]

You do know the knock sensor is a pizeo electric device. It generates a small ac current that the ECU reads. Just because you tap it and it reacts doesnt mean it is funtioning properly.

This is one of the fault codes that when it says bad knock sensor, it is a bad knock sensor.

 

nipper

 

The engine is rapping continuously from bad piston slap. I would think that the impact of the slap would be detected as the impact of detonation by the sensor. With the sensor hooked to the ground strap bracket, it is isolated from the shocks in the engine block, but it is still electrically connected. It doesn't throw the code now I've moved the sensor.

 

I think the computer sees the sensor putting out a knock signal, retards the timing all the way, and it still is putting out a knock signal, so it says the sensor must be bad.

 

Even when it's fully warmed up, the engine sounds like a diesel at idle. tak tak tak tak tak

 

F'n POS 2.5L

 

I'll run this block for a bit, then swap the new heads, waterpump, and timing belt stuff onto another block.

 

It's another 100 bucks for headgaskets down the hole, but what can you do.