Weird air fuel issues, gets worse the more you give it gas. Lean AND rich, any and all help needed!

JagdepanzerJagdepanzer Member Posts: 1
edited March 23 in Subaru
2004 Outback 2.5L spikes low and high fuel trims. At idle they're much more consistent, but as the car idles they slowly get worse. On highway at a constant speed the trims will go through a cycle. It will sit at 0% and then climb up to around 10-20% lean or rich and then pop back to zero. The car backfires after you accelerate hard once, for pretty much the rest of the drive. No smoke from what I've seen, no fuel leaks. It has no logged or pending codes. Can't find any sort of vacuum leak. It gets about 20 MPG (measured at pump), BUT it has gotten 28 MPG highway before! So I know it has the capability (was on a trip back from Tennessee first two fill-ups were 28MPG average), but as of recently it has only been getting 20 MPG highway. Nothing has changed since this occurrence other than me fixing random things!

https://drive.google.com/drive/folders/1ReeCeHp-j2f0vJBq0cLbEmX82mKkj7EG?usp=sharing

I've taken it to the Subaru dealership twice, the first time they said CAT. I replaced the CAT and problem persisted. Second time they said timing or ECU. Timing is correct. I have no way to test ECU as you need to reflash one, but I've heard Gen 2 ECUs are extremely stout and not prone to failure.

Part replaced: Replaced front o2, CAT, injectors, fuel pressure regulator, fuel pump. fuel filter, MAP, brake booster, spark plugs, wires, main coil pack, air filter, redid the headgasket (other reasons), refinished the heads fully, new gaskets. Probably other things I can't remember.

I have a log file, the first few seconds are idle. Then I drive in the city to the highway. I get off the highway, and then back on. At one point, I rev my engine to redline for about 2-3 seconds (someone was about to hit me/louder than horn because muffler fell off). After this point the trims get MUCH worse for the rest of the drive for whatever reason.

ANY AND ALL HELP IS WELCOME AND NEEDED! I WANT TO START WORKING ON OTHER PROJECTS WITH THIS CAR, NOT DEALING WITH STUPID [non-permissible content removed] FUEL CONSUMPTION [non-permissible content removed]!

Comments

  • thecardoc3thecardoc3 Member Posts: 5,559
    Did you inspect the air tube between the throttle body and the air cleaner for tears?
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