EJ25 knock sensor hack job: How to fix?

[ldeikis]

Hi.

 

We bought a 98 Forester a couple months ago and I haven't had much reason to interact with it yet... I've actually only even driven it a couple of times, since it's primarily by girlfriend's car. It threw a trouble code for the knock sensor circuit. Figured I'd pull it out and clean up the connections... lo and behold, after removing all the airbox junk to see clearly, it's clear someone has cut the plug off the god d*mn harness and used a solderless crimp to attach the oxygen sensor!? More digging makes it look like maybe this happened TWICE?! The sensor I pulled out (by accident, thinking the solderless crimp was a bullet connector) was connected to a thin blue wire with a white tracer. Some more digging shows that a 1/4" later that thin blue wire is wrapped in tape, and seems to join a thicker grey wire. What is it with people?

 

Further, the knock sensor that's on there seems to be two wires--a core, and then a sheath that's separated with insulation from the core. The sheath was stripped back, so only the core wire entered the solderless connector. Digging on the net implies this car OUGHT to have a 2 wire sensor. Any confirmation?

 

It was only hooked to 1 wire, and I've got next to no room in there to get at the harness if I want to solder to the original wire and not the blue/white one. Is that sheath just a shield or something? ie, can I resolder just the inner wire, or do I have to tear things out until I can strip enough of the harness away to properly resolder a new connector out of a junkyard or something?

 

What a PITA.

 

I've thought the car was a little down on power, but I just figured a big wagon with AWD might just be a bit more conservative than I expected.

 

Thanks.

 

Luke

[idosubaru]

O2 sensors are sold as generics that you splice in, they are much cheaper than buying the factor originals with the actual plugs. If the plug is still in place, just buy a new one with a plug and install it.

 

As for the knock sensor - same thing - is the original plug still intact? if so just buy one and replace it.

 

if they actually cut the plug off the knock sensor then yeah that should be really awesome to repair as it's hard to get too. In that case i'd just figure out which pins are for the knock sensor at the main engine harness and just run new wire to a new knock sensor. that wouldnt' be that hard or time consuming. i would personally just splice it (properly) right behind the main engine connector - it's the huge one(s) seen under the air intake hose on the passengers side. they are usually bolted to the EJ engines via a bracket unless it's been removed. i would just splice the wire there but if you're really anal you can technically pull the pins out and actually "repin" it but sounds like way overkill to me.

[ldeikis]

Yeah, whoever did this first just cut the plug off entirely, and he did REALLY close to the loom so there's no way in hell I can get at it without major disassembly. I saw that main harness plug you're talking about and had the same thought--it'll be hard to figure out which pins I'm working with, though, since I don't have the other end available to put a meter on... just ONE of the other ends (if I'm correct in understanding I need two wires to the sensor). I can't find a workbook for the car but am thinking of buying one for the slightly later models, which I see available online.

 

I don't have time to deal with it right now so I just soldered it all back up--who knows, maybe it was working and just came loose?--and will deal with it soon.

 

The car DOES need a two-wire sensor, right? If the sensor is on there is only attached with the inner wire, could the outer sheath just be a ground that's being taken care of by the sensor being bolted to the engine? I haven't played with these before.

 

Thanks.

 

Luke

[idosubaru]

O2 sensor should be 3 wire or so i thought.

 

knock sensor, not sure but two sounds right. you could probably just look them up on ebay or thepartsbin.com or advancedautoparts, napa, etc and see a picture to verify for a 98 forester.

 

folks on here can tell you which wires on the harness are needed as the FSM details all of it. just figure out exactly which pin location and wire color pattern and you got it.

 

your 1998 Forester is a Phase I EJ25 so the information should be the same as any 1996-1999 Legacy or OBW with EJ25. i have those FSM's as well as tons of other folks.

 

doesn't matter in a sense where he cut it, the wire is always accessible beyond/on the other side of the connector if need be.

 

*** keep in mind - 1999 and up Forester is a different EJ25 and the information is not likely to be the same.

[GeneralDisorder]

Both of the sensors are going to use sheilded wire back just a few inches into the harness. Where the wires emerge from the harness that sheild is typically folded back and taped, etc. The sheild IS a ground. You can ground it on the engine somewhere if you choose but it's already grounded back in the harness near the ECU, etc.

 

As for the two-wire vs. one-wire deal..... that I'm not sure of. Most of the earlier knock sensors were single wire and grounded through the engine block. Later they went to a 2-wire unit. I *think* your '98 should be a one-wire still because I'm pretty sure it stayed single-wire till they changed to the phase-II engine in '99. You definitely have a phase-II DOHC EJ25D correct? If you have a SOHC engine then you probably have the phase-II (unless the EJ25D was swapped for an EJ22 ).... confused yet?

 

GD

[ldeikis]

As for the two-wire vs. one-wire deal..... that I'm not sure of. Most of the earlier knock sensors were single wire and grounded through the engine block. Later they went to a 2-wire unit. I *think* your '98 should be a one-wire still because I'm pretty sure it stayed single-wire till they changed to the phase-II engine in '99. You definitely have a phase-II DOHC EJ25D correct? If you have a SOHC engine then you probably have the phase-II (unless the EJ25D was swapped for an EJ22 ).... confused yet?

 

I know it's an EJ25, not 22--says so on the block. I don't know enough about these engines yet to even know if it's Phase I or II or R2D2. All new to me. Before we bought it I lay under it with a rag and a flashlight to confirm it has the new style HG, other than that I've hardly sat in the thing til it threw this code. I don't even know if the thing is SOHC or DOHC. It's weird to me to have a car and not a workshop manual. Is the smart move to buy a FSM for the earlier legacy/OBW for the engine, as mentioned above, and a haynes/chilton for the later Forester for body etc? I'd love this car to not need a huge amount of mechanical attention from me--my plate's pretty full with a 30 year old diesel vw as a daily driver--but i'd love to have the info available without harrassing people on the net to look things up on my behalf.

 

So... if the car has the single-wire sensor and the OEM phase I EJ25, then if I just resoldered everything fine maybe it's alright? The light hasn't come back on yet and the car drives fine.

 

Luke

[GeneralDisorder]

I just pulled the manifold from an EJ25D (your engine), and the knock sensor connector is a single wire unit. For whatever reason they switched the connector in like '97 to a 2-wire plug with one of the wire holes plugged off with a rubber plug on the sensor side . So even though it has a 2-wire connector - it's still a one-wire sensor.

 

What *I* would do is go to the junk yard and cut the actual correct body-side connector from a wrecked car and solder that to the harness. Any of the '97 and up EJ25's should have the correct 2-wire plug. Then you can install a new knock sensor - your's may be cracked. It's pretty common. Or you can just grab both plugs and fix your knock sensor's plug as well.

 

GD

[ldeikis]

GeneralDisorder--

 

Thanks for the info. I got a new knock sensor in the mail today and, as you describe, it's a two wire plug with only one terminal in it. I'd prefer to do it right and go cut a harness plug at a pick-n-pull, but NY has some pretty nanny state insurance laws that often prevent you from getting into the junkyard yourself... and I doubt they'd be interested in dealing with the hassle of digging in and cutting off a plug for me at a reasonable price. Before I go ahead and solder I'll make some calls though.

 

If I have to solder it, I think I'll try to trace it back to the big harness plug on the passenger side and try to splice in there. Does anyone have a useful wiring diagram that explains the pins on that plug, or am I stuck poking through it with an ohmeter? I don't mind the meter tactic, just worried if it's an intermittent wiring issue and not the sensor that maybe I won't have continuity to begin with.

 

Thanks!

 

Luke