P0031 & P0051 Woes, post-JDM engine swap - Subaru Outback - Subaru Outback Forums
 
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post #1 of 9 (permalink) Old 08-31-2017, 01:42 AM Thread Starter
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P0031 & P0051 Woes, post-JDM engine swap

A little bit of a relevant back story to this issue to provide the necessary relevant information. Back in November 2016, my girlfriend and I bought an 01 Outback 3.0 LL Bean for a deal at $1500 that went south soon after we bought the car. Long story short, the car overheated terribly and possibly warped or cracked the heads. Weighing our options, we figured the car wouldn't defeat us as it was a beautiful car with a bad heart. Two months ago, I bought a used low mileage JDM EZ30D for it. The swap went great, I paid attention to every detail and preemptively replaced everything preventative that we could on the used engine and everything worn out, or about to wear out on the front half of the car, while the engine was removed.

I finally got the new engine in, started it for the first time and it ran great, revved strong, had a healthy sound to it. We were excited that she roared to life almost instantly, busted out the champagne, the whole celebration ceremony, etc. I noticed it threw a CEL, so I ran the code and got the P0051. The car had no CEL with the old engine installed and we drove it for a few hundred miles before the old engine was pulled, so I figured it was an O2 sensor I forgot to plug in or plug came loose. I had to drop the exhaust manifold again one last time to install new exhaust studs, install the sway bar (subframe was removed when the engine was out to clean it and replace some bushings), and install the hanger for the cat pipe back on the transmission so I never looked into it further.

Got all the parts back together again, made sure both front O2 sensors were connected tight, cleared the code, started it again, check engine light came back on. Now it showed both P0051 and P0031. I checked the driver's side first, found that pins 1 and 2 were popped out a bit on the engine harness, so I repaired the pins. The passenger side found no such issues, so I reset the code and restarted the engine. CEL came back on again, but the engine still ran very smooth. So, I took it out for a test drive. No sooner I get 1000 feet away from my house and the engine stumbled pretty bad and sounds like it's misfiring, horribly. There is also noticeable shake at idle.

The next day, I fired up my FreeSSM on my laptop, and connected the car to it to get some more detailed readings. I got the P0031 code and P0051 went away. Okay. Well the wiring was suspect on the P0051 code, so I figured the faulty connection was to blame. After it stumbled and started running rough, I expected to see a cylinder misfire code, but nothing. I ran the readings for all O2 sensor heaters and I am getting 0 Amps on both front sensors, even on cold starts, and a fluctuation on the rear sensor heater. I also observed no AFR readings from the sensors, despite the lack of codes for that. I perform an emissions readiness test after clearing the codes again, misfire was not detected, but it runs and drives like it's running on 5 cylinders until it gets to about 2000 rpm, but it's noticeably lacking in power. The car on initial startup ran perfect in the garage without a hiccup with the P0051 code set. I even ran it through a couple of burping cycles to get air bubbles out of the cooling system before dropping the manifold and there were no issues.

The O2 sensors never had an issue before, in fact with the cracked/warped head and coolant leaking into the combustion chamber, the car never once misfired or threw a single code. The exhaust manifold was stored in a dry, clean area until it was reinstalled. I have checked for vacuum leaks, no exhaust leaks except the donut gasket after the cats which was there before the new engine, spark plugs were changed and dielectric grease applied to the boots before i dropped the new motor. I used the recommended NGK Iridium plugs (same type of plugs I've used in my other EJ/EG/EZ engine builds), but this engine had not one single "misfire" until the P0031 code appeared.

I've only got another week I can devote to troubleshoot this car as I have to get started on replacing the tail shaft bearings on my Forester and replace a head on my friend's STI. Not to mention, these sensors are $150 a pop, but with the readings from Select Monitor and the fact that they were working prior to the new engine install, I'm not convinced it is defective sensors

Pulled up my diagnostic manual to check out troubleshooting for the P0031 codes. I've gotten down to step 9 where it says to "Measure resistance between front oxygen (A/F) sensor connector terminals. (E47) No.2 - No.1" Check if it reads less than 10 Ohms. Does this mean the connector from the O2 sensor itself or the connector on the engine harness? I think I did this part wrong because initially I tested pin 2 to chassis ground and got no resistance.

Any advice is greatly appreciated.

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post #2 of 9 (permalink) Old 08-31-2017, 06:47 AM
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I've gotten down to step 9 where it says to "Measure resistance between front oxygen (A/F) sensor connector terminals. (E47) No.2 - No.1" . . Does this mean the connector from the O2 sensor itself or the connector on the engine harness?
It's checking at the connector from the sensor itself. That should be the two pins that go to the sensor heater. Although it's not impossible that the heaters on both the bank 1 and bank 2 sensors would go bad at the same time, it's not likely. But they should be checked to be sure. (The heaters are usually in the range of 3 - 5 Ohms. A reading that is essentially zero, or is very high, would indicate an internal short or open circuit.)

At the engine harness connectors to the sensors (E47, E24), pin 2 goes to the main relay, which supplies the power for the heaters. Pin 1 goes to the ECM. The ECM cyclically switches this pin to ground turning the heater on and off, but is not normally grounded. Consequently, neither pin (2, or 1) at the harness connector will show continuity to ground.

Both sensor heaters are supplied by the same Main relay and fuse (SBF-5). When the ignition is at ON there should be battery voltage (relative to a good ground) at pin 2 of the harness connector E47.

Connectors E24 and E47 are part of the engine harness. Did you use your original engine harness or did the JDM come with one? In either case, there's a possibility that the harness has a fault, or the engine harness connection to the bulkhead wiring harness is bad.

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post #3 of 9 (permalink) Old 08-31-2017, 11:24 AM Thread Starter
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It's checking at the connector from the sensor itself. That should be the two pins that go to the sensor heater. Although it's not impossible that the heaters on both the bank 1 and bank 2 sensors would go bad at the same time, it's not likely. But they should be checked to be sure. (The heaters are usually in the range of 3 - 5 Ohms. A reading that is essentially zero, or is very high, would indicate an internal short or open circuit.)

At the engine harness connectors to the sensors (E47, E24), pin 2 goes to the main relay, which supplies the power for the heaters. Pin 1 goes to the ECM. The ECM cyclically switches this pin to ground turning the heater on and off, but is not normally grounded. Consequently, neither pin (2, or 1) at the harness connector will show continuity to ground.

Both sensor heaters are supplied by the same Main relay and fuse (SBF-5). When the ignition is at ON there should be battery voltage (relative to a good ground) at pin 2 of the harness connector E47.

Connectors E24 and E47 are part of the engine harness. Did you use your original engine harness or did the JDM come with one? In either case, there's a possibility that the harness has a fault, or the engine harness connection to the bulkhead wiring harness is bad.
Thanks for that advice. I used the JDM engine harness as I learned it was plug-n-play. I suspected something in the engine harness might be suspect. I will test the O2 sensor wire itself to see if I get resistance on the heater wires. If I do then I'm going to do the tedious task of swapping the two harnesses and seeing if that clears up both my rough running issue and the O2 sensor issues. As you said, it's not likely that both sensors would go bad at the same time and the fact that I get no AFR or heater amperage readings from the front O2 and a fluctuation of amperage from the back O2 points more and more to a harness issue.
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post #4 of 9 (permalink) Old 08-31-2017, 11:28 AM
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@Glennda5id has a 2001 Ez30D swap going,...and may want to offer advice, or want to read this thread,

Steve, what JDM importer did you use and how much did it cost. including shipping to you (if any)?

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post #5 of 9 (permalink) Old 08-31-2017, 12:04 PM
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Yeah, I suspect the engine harness or something at the connection.

The heater circuit itself wont cause engine issues (P0031), but you obviously have other circuit issues and this further leads to believe something is wrong with that harness or the connection. Check to make sure the terminals are clean as the engines plugs may have been disconnected for a while during transport.
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post #6 of 9 (permalink) Old 08-31-2017, 04:22 PM Thread Starter
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Originally Posted by eagleeye View Post
@Glennda5id has a 2001 Ez30D swap going,...and may want to offer advice, or want to read this thread,

Steve, what JDM importer did you use and how much did it cost. including shipping to you (if any)?
@eagleeye

I went through Top Tier Japan. They're located in Phoenix. I had been searching for a while for a good deal and looked on eBay for engines. I came across ones going for $1200+ plus $200-300 shipping. I came across their post at $1,100 with free shipping. Seeing as I only live 120 miles from Phoenix, I emailed them direct and asked if they offered a discount if I were to pick it up. I went down that afternoon and got it for $800 plus tax ($860 out the door) with a 3 month unlimited mileage warranty. The importer said they just got it in and verified 40,000km from their dismantler (which is actually a branch of their company in Japan). Their service was great, real stand up guys who actually know Subarus, they loaded it into the back of my 99 Legacy wagon with a forklift.

It looked very clean. Opening up what I could, there wasn't any varnish in the oil filler, no sludge or varnish on the oil cap, everything looked very clean, almost too clean. The harness tag and the cap have dates of 02.2005 on them, but it's definitely a first generation EZ30D. During maintenance of the engine, the spark plugs (definitely original) were hardly worn out but replaced anyway, the serpentine belt still had very visible markings on it (also replaced), and it had the original serpentine tensioners (replaced with ones from the old engine as it had the updated tensioners). Not a speck of rust at all on the engine (which you commonly see on the more "used" JDM motors). I'd post pictures of it but my post count is too low.

@Glennda5id I'm coming to the realization that the intake is coming off and I'm swapping engine harnesses.
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post #7 of 9 (permalink) Old 08-31-2017, 04:33 PM
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2/05 must have been when they pulled it out of service in the original JDM (99-2002) lancaster

I would swap valve cover gaskets if you have not done so already. or just be ready to watch one leak after a little while.
(typically people jack half the engine to get a little more access ).

____

$800 is a good price, NYC and NJ importers want like $600-$700,

and the ebay JDM importers seem to be just out to rip people off that "only" shop on ebay.

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post #8 of 9 (permalink) Old 08-31-2017, 05:31 PM Thread Starter
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That's what my thoughts were when I saw the year code. It could have been a very late production engine, or swapped under warranty or something. I have the new valve cover gaskets on hand but opted not to replace them because I didn't see any oil residue anywhere on the engine and the original ThreeBond was packed pretty good around the covers. The importer kept it on the shelf with oil inside the engine, they also ran a cylinder compression test on it when they received it to make sure it was as good as they could test it for. It tested over 200 psi in all 6 cylinders.

I'm content with the price I paid. These motors are usually in high demand out here and every quote I received was over $1000 without shipping. Cheapest I found was $600 in Orlando but they wanted $350 for freight shipping with liftgate service to AZ.
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post #9 of 9 (permalink) Old 09-05-2017, 03:26 PM Thread Starter
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Small little update. I tested the O2 sensors. The driver's side O2 had 5 Ohms of resistance for the heater leads and the passenger had no ohms of resistance. The passenger heater is definitely bad. As far as the rough idle, I'm going to replace the donut gasket and re-align the exhaust bracket so it's not pressed up against the transmission, but the project has take a back seat at the moment until I can find replacement transfer gears for my Forester that aren't $300.
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