Sounds like a deisel... Fresh rebuild.

So i rebuilt my 2.5 over the summer, fresh bored cylinders, new water pump, new pistons, polished crank, all the bearings you can think of, broke it in with conventional oil, then changed to synthetic. It had a weird intermittent misfire for like the first 500 miles and that went away. All was good and it ran as smooth as my moms brand new crosstrek. Then I swapped the engine and transmission into my legacy and it started to misfire again only on long trips. (I didnt have any other choice than to drive it because im a broke college kid and had to drive 5 hours to school). Anyway it seemed to run and drive fine, good power, smooth. Recently it has begun to sound somewhat like a deisel and its obviously freaking me out. Its got all new plugs and wires (but not a coil pack). Every once in awhile it goes back to sounding flawless at idle, but goes back to the diesel sound after i turn it off and come back to it later. Im worried it might be injectors (stock). Any thoughts?

 

Thanks in advance!

Any way you could post a video? It is hard enough to diagnose noises in person, more difficult remotely.

Were the valves adjusted?

I'll have to look up exactly how to post a video lol, but yes, I could do that. Yes all valves were adjusted and triple checked

bored out cylinders to what spec? then used stock pistons? forged pistons? what size pistons?

not sure of the exact spec. it was the max oversize you could go ordering pistons through rock auto. Had a great machinist. Decked block, planed heads, etc.

 

I think it was .5mm over stock.

were the pistons matched to the bore by the machinist. he had the pistons in hand when he did the boreing? there are two piston types A and B do you know which you had and were they matched when you bought new pistons. forged or cast pistons?

 

basically i'm trying to get at is its probably just really loud piston slapping its bad when its cold and you said it stops when its warm.

 

and you still have that baja for parts, or the old lego intake? any way you could swap out the ignition coil and see what happens with the misfire?

Pistons were indeed matched by the machinist. Cast pistons, not sure if A or B. It does not go away when its warm. It goes away on a completely random basis. Sometimes on startup cold it runs smooth as ever. Sometimes after I drive it for 2 miles. But it always goes back to sounding awful. Lego intake? Unfortunately, all of my spare parts are 5 hours away at the moment.

first step id take is take a video and post i here, without knowing the nature of the sound were all shooting in the dark.

 

Second would be to get a good length screwdriver and use it like a mechanics stethoscope at various points on the engine while its making the noise to find out where it is originating from, is it in the block, the heads or somewhere else? that can help to find the root cause of the sound.

Then I swapped the engine and transmission into my legacy and it started to misfire again only on long trips.

Thanks in advance!

 

you swapped this engine into the legacy(lego) was there an engine in there already? did you use the intake from that lego? do you have a spare intake sitting around with possibly an ignition coil on it. but all your parts you said are not near you, maybe someone can snail mail it to you, cheaper than a new one for sure, and maybe a wrecker it would further narrow down your misfire situation. do you know if its happening in one cylinder or randomly in different ones?

Grab a Mechanics stethoscope from harbor freight and pin point the noise.

I was also going to suggest the stethoscope from HF. Cheap, and works pretty well. Beats using a old screwdriver or stick of wood for the same purpose, and you can hear with both ears.

 

car runs like a diesel? check timing

Grabbed a mechanic's stethoscope from Harbor freight. Sounds like the noise is loudest in the driver's side head

Check valve clearance. Take off timing cover on that side of the head and check timing mark. You have a video? it could be piston slap

Piston slap

 

A common effect in most Subaru's after having the motor rebuilt. My car sounds like a diesel truck on a cold mornings in the winters, but after 15 mins of driving it slowly goes away, due to the pistons expanding when heated up. What causes this is when the installer set the tolerance on the pistons, he set slightly to the looser side. This is to allow proper piston expansion when heated in the cylinders. Doesn't hurt the piston/cylinders in any way, just the annoying piston slap sound.

 

Once the outside temps are 60* +, you'll notice your cold starts will have very little sound.

Greatly appreciating all of your replies!

 

However, I am still not convinced on piston slap. It runs no different from cold start to operating temp, and outdoor temperature makes no difference either. Also, if it was piston slap, wouldnt I be hearing the sound coming from the cylinder walls more than the head? And it is only on one side of the engine. im leaning more toward a shifted valve adjustment.

 

Thoughts?

 

Thanks!

you should be able to get the stethoscope on the back side of the head near the cam bearing, if its mis adjusted lifter lash you should be able to hear it louder there than just on the head. mine made a bunch of noise when i had it rebuilt as the exhast tightened themselfs to zero lash and the intake loosened up a couple of thou.

 

Id also put the stethoscope on the injectors and see if they are noises, mine make a racket and ive planned on replacing them for the last 20k miles but haven't bothered since they are still going.

YouTube subaru piston slap and compare if the sound is the same or different.

Crank sesnsor

Coil pack

Bad injector

Bad spark plug

Bad knock sensor

 

All can cause screwy issues.

 

Are there any pending codes?

I'll have to look up exactly how to post a video lol, but yes, I could do that. Yes all valves were adjusted and triple checked

 

To post video: Post video to YouTube. Make public. Link here.

Subaru injectors should have a normal audible tick to them.

I used Mahle pistons in a Honda build and the slugs made the engine sound like shit. Nothing wrong, just a characterstic of the pistons.

 

 

Sent from my iPhone using Tapatalk

I used Mahle pistons in a Honda build and the slugs made the engine sound like shit. Nothing wrong, just a characterstic of the pistons.

 

 

Sent from my iPhone using Tapatalk

Is it an auto trans? I had a '99 EJ25 Legacy. Had to get a used JDAM moter to replace knackered iten. JDAM EJ25 had 4 bolt flywheel housing; no problem as it mates to 8 bolt trans. bell housing. After about 10,000 miles horrible noise like rod end failure. Listened with stethoscope; noise coming fro engine, worst on top of crank case. Removed engine, found seriously cracked flex plate. (Couples fly wheel to auto trans). 4 Bolt eng Flex plate is about 2/3 thickness metal of Outback Flex Plate and had cracked all round flywheel bolt holes. Replaced flex plate with heavier item from original Outback motor, noise gone.

If you put your Outback motor into a Legacy, which flex plate did you use?