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I've got this 2000 Subaru Legacy, manual transmission, with a 2.5L 4cyl. I've been getting occasional codes for bank 1 system too lean for a couple years now, but haven't had many issues with it and the car doesn't usually have any problems.

However, recently it started missing something fierce. I've only pulled cylinder 2 and cylinder 4 misfire codes off of it since it started running funny, and I've tried everything.

I've tried:

  • Plugs, Wires, and Ignition Coil
    • Platinum plugs and store band wires. Tried a replacement coil but didn't notice a change so I went back to the original.
  • Vacuum hoses
    • Replaced cracked vacuum hose going from intake manifold to fuel pressure regulator - that was probably causing my occasional lean condition on that side
    • Also replaced vacuum hoses going to the EVAP Purge Solenoid (aka valve) under that side of the intake manifold
    • not finding any vacuum leaks anywhere using the carburetor cleaner spray method
  • Fuel pressure test
    • Fuel pressure before fuel filter is well within range, both with and without the fuel pressure regulator plugged into vacuum.
    • It's important to note that the fuel filter was replaced less than a year ago, and I've replaced it just about once a year for the past 3 years I've owned it.
  • fuel injectors are ticking
    • The o-rings were replaced on those about a year ago, too, fixing a pretty massive vacuum leak which I have double checked and is no longer there.
  • Fuel system cleaner
    • It's been running on 8 gallons treated with 21gal gumout complete treatment for a few hours now, and it doesn't seem to be improving. That cleaner is capable of removing water as well as treating the system.
  • Compression test
    • all cylinders are building within 2-3 strokes to within parameters. All cylinders are behaving the same way, too, so one would expect that both sides of the engine would be misbehaving, not just one.

There are no other codes getting pushed, and I do have a scanner capable of giving me live data, although I really don't know what to do with the data it's giving me, tbh.

The only thing I'm noticing is that the EVAP canister purge solenoid is repeatedly ticking something awful when it's told to open, just ticktickiticktick the whole time it's open, and it's loud.

I'm at a loss, and wondering if someone out there might have an idea of what to look for next. Thanks in advance, and comment if you need more info - I'll get it ASAP.

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If you are getting a lean condition on a cylinder, it has to be fuel related or a vacuum leak. Since you suggested you have checked and cured at least one vacuum leak, I will assume this is not your issue. If it were spark related, it would be a rich condition. You've checked fuel pressure to be good.

This leaves a problem with a fuel injector, which is not working correctly, either not opening fully or partially plugged. The easiest thing to do to see if this is actually your problem is to swap out two injectors. If the problem follows the injector, it will show up as a lean condition on the cylinder you swapped the injector to. If it stays at the same cylinder, it could be that you have an intermittent electrical gremlin at the #1 which would not fire the injector correctly. This situation would be a lot harder to diagnose.

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  • The lean condition isn't presently showing up. Although that issue may still be happening, as the ECU only showed the code intermittently, I s merely giving some context. However: the lean condition was bank 1, which usually means the side of the engine with cylinder 1. The misfires are happening on cylinders 2 and 4. If "bank 1" means the driver's side of the engine, where cylinder 2 is, then you might be on to something, however the misfires are happening on more than one cylinder. 2 injectors going at the same time would be rather unusual.
    – FireSBurnsmuP
    Oct 31, 2015 at 17:56
  • Most likely ... I think I misread or missed part of your question, so apologies. Still, if you switched the injectors from one side to the other, you'd be able to tell if it's injector based, or eliminate them as an issue. Also, I'm not sure if Subaru 4-cyls use bank 1 & bank 2. The easy way to tell is, how many O2 sensors are there pre-cat? If only one located at where the exhaust pipes all come together, you'll only see bank 1 and never bank 2 (so don't use that as a litmus test).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 31, 2015 at 18:03
  • Okay. I'll have to double-check that I only have 2 O2 sensors. My scanner only picks up values from 2, both listed bank 1, so this may be the case. I might have to try the injectors, but I should note that swapping fuel injectors is not a trivial task on this engine. The manual transmission version of the motor doesn't have clips to hold the injectors into the fuel rail, and the top injector o-rings are extremely delicate. Doesn't help that the driver-side fuel rail wraps around the intake manifold, either. I used 6 sets of o-rings on 2 cylinders, so I'm not itching to tear that apart again.
    – FireSBurnsmuP
    Oct 31, 2015 at 18:09
  • Yah, what I'm suggesting is one pre, one post cat converter.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Oct 31, 2015 at 18:19
  • It does appear that I have only 2 O2 sensors, so any lean conditions could be anywhere. I'm not sure if the lean condition is still happening, of course, but it looks like Fuel Injectors are probably my biggest concerns. While my scanner is only picking up a Cylinder 2 misfire right now, it was seeing cyl. 4 earlier as well, and it would seem odd to me that 2 injectors would go at the same time. I'll keep updating with new information as I find it.
    – FireSBurnsmuP
    Nov 3, 2015 at 19:31

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