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Old 11-10-2017, 01:07 PM   #1
ScubaruImpreza05
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Question 2.5i running terrible; replaced Cam and TPM sensors already

First off, the engine is from a 2012 Legacy 2.5i. We transferred over the necessary sensors between the Impreza 2.5i which had 110k miles on it. For all intents and purposes, the engine and most sensors are a '12 Legacy 2.5i motor. ECU is Impreza 2.5i. Oil pan and pickup are from the Impreza 2.5i.

Additional parts:
Rallysport 2.5i headers
Williaty's Hybrid intake
Lightweight full size crank pulley


So, we swapped the engine in with 19k miles on it. The engine ran fine for a little while after the swap was done. We had burned the center diff up shortly before swapping the engine. The car was used lightly after the swap for a few months, when suddenly it began to idle rough, and would sometimes stall out after pushing the clutch down. Acting very similar to right after an ECU reset. No CEL. We replaced the TPM and cam sensors hoping it was one of those, no dice.

It has sat for over a year with little movement, and I am going to try and fix whatever the hell is going on with it soon. I have a OBD2 scanner and reader in which I can see all sensors and voltages while the engine is running. Problem is, I have no idea what that info means. I want to fix this so I can beat it again on for Rallycross, and also to learn more about the engine.

So asking, any ideas? Maybe a bad MAF sensor? Some sort of oil sensor going wonky and tripping limp mode? I don't know where to start, so looking for direction. Will have this car in my hands in a day or two.

My one concern is somehow maybe the oil pressure isn't right. We had to swap the pickups and they weren't a 100% direct fit, we had to tap the block to make mounting holes for the Impreza pickup to fit onto the Legacy block. We also swapped the Impreza oil pan over and it fit the gasket, but we had to tap an extra bolt to seal it properly. Anywhere on the block I can verify pressure?

Thanks all, and I'll post up some cold sensor reading and warmed up sensor readings when I get my hands on it.
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Last edited by ScubaruImpreza05; 11-10-2017 at 01:17 PM.
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Old 11-10-2017, 10:20 PM   #2
Chump Car Subie
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I'm no expert by any means, but I had a crappy running 2.2 impreza that I just recently resolved. It had a hard time starting and would miss really bad under full throttle high rpm. I did a basic tune up, plugs, wires, fuel filter, and also replaced the coil pack and injectors with ones that came from a known running engine as the injectors ohm tested kind of high. I think the injectors and either the plugs or wires were the culprit or a combo of the two because the miss disappeared after I replaced those items and it starts up nice as soon as the starter hits I'd recommend to start simple with a good tune up even if it doesn't have many miles
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Old 11-12-2017, 10:21 AM   #3
Elbert Bass
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Ran OK and then it sat for a year? No codes? Might be your gas is bad after sitting. That's the first thing I would check.
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Old 11-12-2017, 12:34 PM   #4
2slofouru
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I did this swap a while back on my 06 2.5i, with a 12 legacy block at 7k miles, hasn't had a problem since then and I drive it almost every day. The fuel could be crapped out like others have said, otherwise you're going to need to check for codes and go from there.
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Old 11-12-2017, 08:58 PM   #5
H_wells3000
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unplug your maf, does the car run any better? unplug your front O2 sensor, does it run any better now? These are quick free easy ways to narrow down an issue. Obviously reconnect and reset ecu (disconnect battery for a min) after your done testing
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Old 11-20-2017, 09:53 AM   #6
ScubaruImpreza05
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So, sorry for the delay on this, life got in the way but I was able to get to the car yesterday. Something is not right with the valvetrain. It sounds like there is no oil getting to the top ends of the engine, the valve noise is so loud. Oil was 3/4 full on a cold check, and no oil light came on the dash, but something isn't right. I am not sure it is something I can reasonably diagnose and handle. Are there any plugs or lines on the top end that feed the valvetrain that I could pop open and see if oil is coming up through?

I took a video of the valvetrain noise. The odd part is that when it initially starts, the noise isn't as bad, but 5 seconds after the engine is running it picks up in intensity, and follows the RPM of the motor. I didn't have a scope on hand, but it sounds like it is coming from the center of the motor underneath the intake plenum, which is worrisome, as the top ends are on the outside of the motor. There is no oil smoke coming out of the exhaust, even on a cold start, so engine oil isn't getting into the combustion chamber.

I'll try to get a high quality video up as an example. I took one but haven't uploaded it yet.
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Old 11-20-2017, 10:03 AM   #7
ScubaruImpreza05
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Here it is, the valve noise and engine load changes for no reason at about the 13-14 seconds mark. Maybe some form of electronic timing/ECU issue, since it doesn't happen right away? (PS - yes that's a mouse nest, but amazingly nothing looked chewed up, but the engine needs a washing for sure. )

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Old 11-20-2017, 04:17 PM   #8
yarrgh
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I can't tell if it's the frame rate, but your AC is on and doesn't seem to be turning quickly. Turn it off (and defroster) and see if that noise goes away.
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Old 11-20-2017, 11:18 PM   #9
Charlie-III
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Quote:
Originally Posted by ScubaruImpreza05 View Post
So, sorry for the delay on this, life got in the way but I was able to get to the car yesterday. Something is not right with the valvetrain. It sounds like there is no oil getting to the top ends of the engine, the valve noise is so loud. Oil was 3/4 full on a cold check, and no oil light came on the dash, but something isn't right. I am not sure it is something I can reasonably diagnose and handle. Are there any plugs or lines on the top end that feed the valvetrain that I could pop open and see if oil is coming up through?

I took a video of the valvetrain noise. The odd part is that when it initially starts, the noise isn't as bad, but 5 seconds after the engine is running it picks up in intensity, and follows the RPM of the motor. I didn't have a scope on hand, but it sounds like it is coming from the center of the motor underneath the intake plenum, which is worrisome, as the top ends are on the outside of the motor. There is no oil smoke coming out of the exhaust, even on a cold start, so engine oil isn't getting into the combustion chamber.

I'll try to get a high quality video up as an example. I took one but haven't uploaded it yet.
All the oil "lines" are internal passages, thus no line to remove and check.

Since it sat a while, maybe gunned up tappets that is causing the sound.
Also sorta sounds like an exhaust leak.

Check oil pressure by removing the low pressure switch sorta under the PS pump and install a mechanical gauge.

Quote:
Originally Posted by yarrgh View Post
I can't tell if it's the frame rate, but your AC is on and doesn't seem to be turning quickly. Turn it off (and defroster) and see if that noise goes away.
Agreed, kill the AC/defrost so the AC compressor is offline.

PS, hope you mean "TPS" not TPM, why is a Tire Pressure Monitor (TPM) a question in how an engine runs?
LOL........

Last edited by Charlie-III; 11-20-2017 at 11:26 PM.
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Old Yesterday, 10:35 AM   #10
ScubaruImpreza05
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Join Date: Nov 2004
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Vehicle:
2006 2012 Weee-strom
SV650 For sale

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Quote:
Originally Posted by Charlie-III View Post
All the oil "lines" are internal passages, thus no line to remove and check.

Since it sat a while, maybe gunned up tappets that is causing the sound.
Also sorta sounds like an exhaust leak.

Check oil pressure by removing the low pressure switch sorta under the PS pump and install a mechanical gauge.



Agreed, kill the AC/defrost so the AC compressor is offline.

PS, hope you mean "TPS" not TPM, why is a Tire Pressure Monitor (TPM) a question in how an engine runs?
LOL........
Ok thanks, didn't realize about the AC, but you are right. And it is frame rates, it was spinning fine but I do recall the compressors on these engines take out a considerably chunk of power.

Also, yes, TPS haha my bad.

I will look into these suggestions. The exhaust leak might be an issue, I'll check it. It has the Rallysport 2.5i headers on with fiber wrap so there isn't as much muffling the exhaust sound as the stock headers with their thickness and guards and also EPA governed catalytics.
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