1991 Legacy Sport throwing many wacky codes

[Amoxin]

Hey guys and girls. It's my first post and I'm asking for advice, sorry! I have spent some time on the forum trying to figure this car out, no luck yet though! I figure before I whip out my volt meter and start checking things, I would post up and share what is going on with my Subaru.

I'm all about solutions, and something I see a lot lately is people asking questions on a forum, people getting answers, and then the people never post back with what the solution was. I'm not that guy, I'm going to post an answer once one is found.

Ok, so now that you know where I am coming from, here is the dilemma.

I picked up a clean 1991 Legacy Sport with a pretty low mileage EJ22T mated to a 5 speed tranny under the bonnet.

The engine sounds really good and starts up normally every time, but when I accelerate, it will hesitate and ends up approaching redline in a much more awkward manner than one would expect. The check engine light pops on after a battery reset within about 5 minutes of normal driving, so this is certainly not an intermittent issue. The codes that I pulled are...

14 Fuel injector inoperative (Abnormal signal emitted from monitor circuit)

15 Fuel injector inoperative (Abnormal signal emitted from monitor circuit)

16 Fuel injector inoperative (Abnormal signal emitted from monitor circuit)

17 Fuel injector inoperative (Abnormal signal emitted from monitor circuit)

22 Abnormal voltage produced in knock sensor monitor circuit

23 Abnormal voltage input entered from air flow sensor

24 Air control valve inoperative (Abnormal signal produced in monitor circuit)

32 Oxygen sensor inoperative

41 Faulty learning control function

49 Use of improper air flow sensor


In my experience with lots of sensor codes, it usually ends up being the ECU that fails. I am unfamiliar with the Subaru setup though, so I'm really hoping that it is just one or two sensors that have gone out, throwing everything else out of wack.

I think the wrong air flow sensor is in there, PO stated he changed it with one from a NA Legacy from a similar year.



In advance...Thanks for the help!

[Deride]

I would start with the ignition relay. Also check your engine harness connectors behind the battery for corrosion or broken wires.

[Rubasu]

get a turbo maf.................

[Tommio RS]

I agree with the getting the right maf and going from there.

[Amoxin]

Good advice on the engine harness, I found a wire in the 8 pin connector that had some corrosion on it, still working with the same symptoms though.

I ran a test on the O2 sensor and concluded that its either clogged or just toast due to its output of 0.20v regardless of engine rpm/temp. I swapped the coil pack and put some newer spark plug wires on it. During that process I ended up finding a lot of rusty water in the rear left spark plug hole.
After cleaning out all of the water I found that while it approaches red line much more quickly, it still has the hesitation.

Tomorrow I will remove the O2 sensor and make sure it's not just clogged before I replace it with a new one. I will also be picking up the old air flow sensor from the PO. If I don't find a difference with those two sensors, I will test the ignition switch.


Thanks for the quick response guys.

[cj91legss]

have you checked out your fuel pump? Your fuel pumpcould be old and cutting out when the engine is demanding more fuel.

[Amoxin]

I was able to confirm that it has the right air flow sensor and although the old O2 sensor was dead, the new one has made no difference. I pulled spark plugs, seeing that the old ones were much too old for a standard NGK V-Power plug, they were replaced. As were the spark plug wires. Still no difference.

Today I swapped coil packs which didn't seem to change my symptom, and I also tested fuel pressure and fuel regulator which are both in good shape. I did not drive with the pressure tester connected though...I think I will try that.

I have noticed something a bit odd...I cannot seem to clear the codes, even after leaving the battery disconnected all night. I pulled the ECU thinking it may be toast and saw no visible burns or hot spots. Is ECU failure common?

When driving with D-check enabled the only code that flashes is 22, which is the knock sensor. I moved the knock sensor to a different location, as others have done with some success, but the knock sensor code still pops up when driving.

During test runs, I have found that it seems to run a bit better before its been heated up, after it gets hot, I find that the hesitation or bucking can get pretty intense. With low amounts of throttle input, it behaves prefectly normal. As soon as you start the put your foot down and load up the engine, it quickly misbehaves.


I have not yet checked the ignition switch, but I have jiggled the key during the bucking sessions and it does not make a difference. I'm currently looking for a schematic to test it.


Maybe I have a fuel filter that is still flowing, but only for lower rpm?

[cj91legss]

I find that the hesitation or bucking can get pretty intense. With low amounts of throttle input, it behaves prefectly normal. As soon as you start the put your foot down and load up the engine, it quickly misbehaves.

That is EXACTLY what my car was doing, down to the t......

I could ease into throttle, but as soon as i punched it, it's like the fuel pump got over loaded... my car had sat for 9 -10 months, then i got it running again, and shortly after i started having this issue. finally one night it just died on me on my way home from work.

luckily some buddies of mine were nice enough to drop everything he was doing and help me out (Thanks Eric & kris) we tested the pump when he got there, and it was obvious that some sort of bearing had crapped out inside of it.

[Amoxin]

cj91legss - fuel pressure at idle is 28psi, and under load at about 4000 rpm it is 42psi. I cannot find info anywhere on what it should be. Thanks.

[Legacy777]

Since the knock sensor is the only code that won't clear I would suggest either replacing the knock sensor, but before doing that, I would suggest checking the resistance on the knock sensor wiring from the connector in the engine bay (going to the ECU) to the pin at the ECU.

Over time the wire gets brittle and cracks, and you lose all continuity on that wire. If this is the problem the best way to fix it is to use some microphone wire (since it's shielded) and run a new wire from the ECU to the knock sensor and solder the existing connectors to it.

If the wire checks out good, I'd suggest replacing the knock sensor, they are notorious for cracks in the plastic case, which cause it to short out. There was a design change, and the new ones have a white connector vs. the original gray connector.

The engine running issues you describe are likely in part to the car running in limp mode due to the knock sensor.

[Amoxin]

The new white connector knock sensor has gotten the car out of limp mode and has also fixed the issue where my codes would not clear. I now have no CEL and nothing pops up in the D check. It still hesitates, just not as badly. It seems to still fluctuate in severity.

I moved the location of the knock sensor to the top of the bell housing and torqued it correctly. I wonder if I should install some felt in between the KS? I have heard of some people having success with this when their subies are acting up.

Also, testing the TPS via Surrealmirage's website, I bump into an issue where my signal wire to the ecu is on the number 1 pin where it should be on the number 2 pin in the diagram. Anybody have a color code for this handy?

Thanks for the help, it's much appreciated.

[Legacy777]

Did you "reset" the ECU after replacing the knock sensor? Clearing the codes & resetting the ECU are different. To reset the ECU, pull the EGI/TCU fuse No 14 for about an hour.

Here's the testing procedure and wiring diagram.

http://www.main.experiencetherave.com/s ... sting1.jpg
http://www.main.experiencetherave.com/s ... sting2.jpg
http://www.main.experiencetherave.com/s ... sting3.jpg
http://www.main.experiencetherave.com/s ... g_diag.jpg

[Amoxin]

I did not reset it. Good idea

[Amoxin]

Well, I tried it and wasn't able to get anywhere. I decided to sell it and keep my eyes out for another. Thanks for all the help!