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I posted this in the Gen 2 forum and was told to also post it here. Post below:

This is my first post and I'm not very experienced working on cars, and I'm at my wit's end trying to track down this problem. This requires a short story:

I have a 2000 OBW 2.5 MT with 166k miles on it. I replaced the engine for other reasons, and now I'm starting to regret it. Ever since the engine swap, it's been throwing a P0172 Bank 1 System Rich - no other codes ever - and has been incredibly sluggish (read: flooring it in 4th trying to accelerate to highway speeds and barely speeding up enough to make the on-ramp). The engine was a JDM model but all parts used were from the original engine (manifold, sensors, injectors, etc), throttle body was cleaned, and there were no vacuum leaks according to the mechanic. Throttle body was cleaned during swap. The CEL came on after the swap, and the loss of power was immediately noticeable.

Mechanic said the coil and wires were corroded, so I replaced them along with the spark plugs. the PCV valve was gummed up as well so I replaced that too. Reset the CEL, drove it ~15 miles, light comes back on and the engine is still sluggish. Mechanic then says the front O2 sensor is fluctuating wildly, and needs to be replaced. I said go ahead and replace it. No change, CEL back on. He re-replaces the sensor under warranty on the off chance the replacement was bad. No change, CEL back on. He said to order a MAP sensor, which I did and am waiting for it to arrive. In the meantime, I got an OBDII cable and OBDwiz and took a look at some parameters. I picked a handful that I thought would be helpful but if you have any more suggestions, I can take more readings. The trace is a ~5 min capture of idling where I revved to 2k at the 175 sec mark until the 250 sec mark. The rear O2 sensor (B1S2) reading looked strange to me, but I don't know exactly what to make of it.

TL;DR: P0172 and large power loss after engine swap. Replaced plugs, wires, coil, PCV valve. Problem persists despite typical mechanic quick fixes. No idea where to go from here.

Any help is appreciated. Thanks in advance.
engine paramters graphs.PNG
 

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2001 VDC/SC One of a Kind
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The ECM is reducing it's fuel feed to keep the engine running at 14.5-14-9:1. The code is telling you too much fuel is being delivered under normal computer management. The STFT is verifying it with the negative value.

First off, you need to find another shop to do the work on your car. He's throwing parts at it because he doesn't know what the problem is. In other words, he's a mechanic who changes parts, not a technician who finds the problem.

Next, the MAP sensor doesn't seem to be bad.

If there is an AF sensor other than Denso on the car, that could be causing a problem.

Other things that may be wrong, even with an engine swap, is the timing may be off enough to effect combustion but not misfire. The grounding on the engine is poor. The fuel pressure regulator is bad and fuel is being pulled in to the intake stream. The purge valve is stuck open.

You would need to find out why the cylinders are getting too much fuel, or, not burning it all. The ECM manages fuel based on the MAP, TPS, ECT & AF sensor feedback. The injectors supply fuel, the spark plugs fire via the coil and cables, air is routed through the intake and valving. Somewhere the mix is screwed.

Don't discount you moved a problem from the old engine to the replacement either. Why did the engine get swapped?

And that rear O2 data is useless until you get the engine running correctly.
 

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Thanks for the insight, cardoc. I found a new shop that'll hopefully do their do diligence this time and properly diagnose the issue. I'm also holding off on changing the MAP sensor as of now. There's no other AF sensor other than the Denso that was replaced twice. The grounds look okay but I'll have the shop double check.

I checked compression myself and got 210-215 psi in all cylinders. I don't have the FSM but that seems high to me (which I guess is better than low) but after testing I dropped the pressure gauge so it now reads 60 psi, I'm unsure if retesting would prove helpful. Ugh.

The engine was swapped because, unbeknownst to me, it was burning a LOT of oil and was 3 quarts low by the time I discovered this. The engine stalled on the freeway and ran for ~2 miles after refilling the oil before it just wouldn't start anymore. The shop I took it to told me it was toast.

I don't have any info on the new engine other than it's a JDM model with "60k miles" according to the seller. It's from ebay and the seller has been responding to my messages so far.

I took another drive with the engine warmer and with more parameters logged. Let me know if anything new sticks out. Thanks again.


drive #2 graphs.png
 

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The long term fuel trim indicates it's not burning all the fuel and is running rich. It would be good to see STFT for bank 1, sensor 1, that's the AF sensor feedback adjustment. The AF voltage being all over the place is because of the throttle position based on what your foot was doing. A steady drive would be more indicative of the fuel trim feedback.

The MAP is working.

The JDM engine is probably a 2.0L. Less HP and Torque than the 2.5, but not enough to really notice unless you are gunning it on an on ramp. A little slower acceleration.

I'm still thinking timing belt misalignment or tensioner is worn and not holding tension on the belt. Other things would be poor conductance from the battery to the engine and computer.
 

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Discussion Starter #6
The long term fuel trim indicates it's not burning all the fuel and is running rich. It would be good to see STFT for bank 1, sensor 1, that's the AF sensor feedback adjustment. The AF voltage being all over the place is because of the throttle position based on what your foot was doing. A steady drive would be more indicative of the fuel trim feedback.

The MAP is working.

The JDM engine is probably a 2.0L. Less HP and Torque than the 2.5, but not enough to really notice unless you are gunning it on an on ramp. A little slower acceleration.

I'm still thinking timing belt misalignment or tensioner is worn and not holding tension on the belt. Other things would be poor conductance from the battery to the engine and computer.
Interesting. The STFT for B1S1 doesn't show up as an available parameter on the program I'm using.

I just had a Subaru-specific mechanic take a look at the engine and it is, in fact, an EJ20. His hypothesis: because the injectors are from the EJ25, they're expecting a larger engine and injecting more fuel. The ECU can't be tuned to account for this (according to mech), so it will always inject more fuel and always run rich. He suggested possibly refitting the JDM injectors to see if they limit the amount of fuel being injected, but there's no guarantees that it would work. He also mentioned the smaller size could definitely account for the loss of power I'm seeing.

I'm going to take this up with the ebay seller because they listed this engine as a "replacement for EJ25" but, while it technically fits, it is a smaller engine and does not function as it should.
 

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Your engine came with an intake and injectors?
Yes, but the mechanic that did the swap said that they used the manifold and injectors from the ej25 when installing the ej20. I don't have access to the intake and injectors from the ej20 anymore.
 

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Well that's inconvenient for a swap and see point of view.

Although I don't think the latency between the two engine's injectors is so different that it will cause this. I've swapped an EJ20 in for an EJ25 before and did not have an issue when using the 25s intake system and harness.

I believe something else is awry and the mechanic is missing it.
 

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Well that's inconvenient for a swap and see point of view.

Although I don't think the latency between the two engine's injectors is so different that it will cause this. I've swapped an EJ20 in for an EJ25 before and did not have an issue when using the 25s intake system and harness.

I believe something else is awry and the mechanic is missing it.
You were right about the timing. They checked the timing belt and sure enough, it was off by 2 teeth on either side. Also, it was missing a timing belt guide which, according to the mechanic, meant that the engine was from an AT car. I've driven it ~50 miles since the timing belt fix and it feels much better than before. It doesn't shake when idling, the power is back (more or less - it does feel like a smaller engine, but it's not problematic), and the CEL hasn't come back on. I took some more driving data for posterity, I was doing approx. 65 mph on cruise control starting at the ~25 sec mark.

Thanks for the advice so far, I'm glad I insisted they check the timing. The mechanic is still hung up about the injectors, though. I'm thinking as long as the evap system clears (need to recheck with less gas in the tank) and I can get it smogged here in CA, I don't really mind.

481513
 
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