LGT Spark Plug Replacement

Over the last 5000 miles or so, have noticed a drop in power. Stage II -> just above Stage I ish drop on the butt dyno. Same Shell 93 Octane. Just hit 44,444 miles and change the plugs.

 

This is my 5th Subie but first with turbo. There is a wealth of info on this forum and others. Bottom line recommendation is to din't until 60K miles to change the plugs. My engine could not agree more.

 

One thing to note is the 5th gen plugs (NGK SILFR6B-8 gap @ 0.032)are different than 4th gen (NGK SILFR6A gap @ 0.030).

 

http://www.ngksparkplugs.com/part_finder/car_truck_suv/results.asp

 

The service manager stated plug replacement on the Legacy involved lifting the engine up to gain clearance. So I had them do the replacement. Anyone else change them yet?

 

The plugs were changed. Did it make a difference?

 

:wub::wub: Yup back to full power.

Edited October 6, 2017 by GTEASER
changed spark plug gap from tenths to hundredths, wrong decimal place.

I knew it was a tight fit but didn't know they had to lift the engine.

 

Are you on a protune or OTS?

1.5 hours labor

 

pro tuned by Chris @ EFI Logics

 

Opps!! Forgot to reset the ECU to relearn after the new plugs ..... got to go!

I'm yet to break 20k so I've got a while before this hits. Good to hear your recommendation on when to change though since it's only a matter of time.

Did you go with the stock plugs or one step colder?

Stock

 

From everything I read, Stage II is not making enough power to warrant a colder plug. If it needed it, I would have changed it out when going to Stage II protune.

good to know. 1.5 hours labor sounds like it is worth it if they have to lift the engine.

That's like 6 of my hours plus a trip to the hardware store or two to get an extension, wrench, socket, pull bar ...

Yeah...i have no room for an engine hoist, and for the $ would just rather pay a shop. Crazy it is that complicated. And I thought F-body plug changes were a PITA

Did you go with the stock plugs or one step colder?

 

I'd like to ask, would one want a step colder or a step hotter plug? I fiddled with a BMW 320i Engine and it liked the step hotter plug. Much better torque at the lower end. Am not sure though on the higher end on a sustained basis though.

 

Would putting in a hotter plug wreck the engine? I d be interested if it improves fuel economy for example.

 

thanks

I would not go with a hotter plug on a forced induction engine.

 

And changing spark plugs isn't going to give you better fuel economy, unless your plugs were already fouled up to start...

Interesting. Text below is from the 5th gen service manual (GT engine). No mention of lifting the engine. Fairly simple task, according to the shop manual...

 

2. Spark Plug

A: REMOVAL

Spark plug: Refer to “SPECIFICATION” for the spark plug. <Ref. to IG(H4DOTC)-2, SPECIFICATION, General Description.>

 

1. RH SIDE

1) Disconnect the ground cable from battery.

2) Remove the air cleaner case. <Ref. to IN(H4DOTC)-8, REMOVAL, Air Cleaner Case.>

3) Disconnect the connector from ignition coil.

4) Remove the ignition coil.

NOTE: Turn #3 ignition coil by 180 degrees to remove it.

5) Remove the spark plug with a spark plug socket.

 

2. LH SIDE

1) Remove the battery. <Ref. to SC(H4SO)-26, REMOVAL, Battery.>

2) Disconnect the connector from ignition coil.

3) Remove the ignition coil.

NOTE: Turn #4 ignition coil by 180 degrees to remove it.

4) Remove the spark plug with a spark plug socket.

 

B: INSTALLATION

1. RH SIDE

Install in the reverse order of removal.

Tightening torque (Spark plug): 21 N·m (2.1 kgf-m, 15.5 ft-lb)

Tightening torque (Ignition coil): 16 N·m (1.6 kgf-m, 11.8 ft-lb)

 

2. LH SIDE

Install in the reverse order of removal.

Tightening torque (Spark plug): 21 N·m (2.1 kgf-m, 15.5 ft-lb)

Tightening torque (Ignition coil): 16 N·m (1.6 kgf-m, 11.8 ft-lb)

 

C: INSPECTION

1) Check the spark plug for abnormalities. If defective, replace the spark plug.

Thanks for the last post. Is there anything different for turbo over NA? Maybe I got smoked...

Turbo recommends pulling air box and battery for better access.

 

Non-turbo H4 recommends pulling air box but leaves battery in place (but disconnected).

 

H6 is the worst. It requires removing air box, battery, battery carrier and a few extra brackets for access and shows detailed diagrams for chaining multiple extensions and a universal joint to get to the plugs.

 

No mention of lifting the engine for any of them, though I imagine it probably would make life easier. Those side mounted plugs were never much fun to change in the 4th gen (haven't personally tried 5th gen yet). Can't beat an I4 in that regard.

Edited October 28, 2011 by Kenpachi

The spark plug replacement is the same on the 5th gen as the 4th gen. 1.5 hrs labor is the same all the way back to the first Subaru's. If you have to lift the engine, and it takes you more than an hour to actually do the work, you shouldn't be a line mechanic working on Subarus.

 

Your new 0.032" gap is better for emissions and economy, but not better for power.

A normal gap for a modified turbo is around 0.028". On E-85 we run 0.023"

 

A one step colder plug will help prevent detonation no matter what level of power you are at. The downside to a colder plug is they can foul easier. If you floor the car everyonce in a while, they'll get hot enough to self clean.

 

Stage 2 is probably the first point you should consider colder plugs.

Edited October 28, 2011 by mwiener2

Slightly off topic, but how do you lift the engine in the 5th gen?

You don't. There is no need to unless you need to change engine mounts or pull the engine. If you can't figure out how to lift it a few inches, you shouldn't be doing either of those things.

Front sway bar requires the engine to be lifted....I was just curios if the only way to lift is like described in the service manual, via a hoist.

 

Past cars it was as simple as disconnecting the engine mounts and finding a suitable location to jack the engine up from...

You 2010 guys are silly

Bump from the ancient archives as I will be doing this soon.

Did it a couple weeks ago.... 1st time on a fifth gen. Pretty straightforward - it is just very tight. Only pro tip I have to add - either snip the cable tie holding the wire for the rear, drivers side coil pack or unplug the connector to that coil pack. Otherwise, you will be unable to rotate it 180 degrees to get it out.

I have a 2005 LGT and plugs are not a problem with a little time to spend. Remove airbox, etc and described above after pulling car up on ramps or jack stands. Remove both 14 mm engine mounting stud nuts, and get a short 4X4 block of wood and jack up the side you're working on a few inches to get the coil packs exposed above the frame.

 

Do one side at a time and you don't have to pull the dogbone trans bolt out.

I have a 2005 LGT and plugs are not a problem with a little time to spend. Remove airbox, etc and described above after pulling car up on ramps or jack stands. Remove both 14 mm engine mounting stud nuts, and get a short 4X4 block of wood and jack up the side you're working on a few inches to get the coil packs exposed above the frame.

 

Do one side at a time and you don't have to pull the dogbone trans bolt out.

The 5th gen engine mounts differently than the 4th gen.

 

Sent from my SAMSUNG-SM-G920A using Tapatalk

I replaced my plugs about a month ago for maintance. Ive got 120k on it now. I did not have to lift the engine. the right bank is easier to service then the left after removing the air box. you will have to rotate the coil as you remove it to get it out so its kinda of a puzzle but not bad really. the most challenging part i thought was just getting the coils unplugged. took me about 35min to do all from above didnt need to lift the car. i am an ase certified tech with 12yrs experience so im used to working in tight areas. just saying might take you longer but theres no need to waste time and energy lifting the engine

This was not fun. The one closest to the driver is the one. Cut the harness clip, Rotate 180 degrees, and work every little available space.

 

I'd suggest for that one either a short one inch extension or attach the socket knuckle right on the spark plug socket.

 

Don't lift the engine.

 

Sent from my SM-G955U using Tapatalk

Edited January 22, 2018 by Starks