LGT Spark Plug Replacement

[ehsnils]

The only difference between the ILFR6A and the ILFR6B is the built-in resistor for RFI dampening. 1kOhm for the A and 5kOhm for the B.

 

Gapping a spark plug to a different size is a tuning trick that may be needed if you go outside stock. Just check and adjust gaps before installing them. Some tuners even look into aligning the ground electrode in the engine to get an optimal flame front propagation.

 

The DILFR6 plugs have a different design on the ground electrode that's intended to improve the flame expansion even more: https://www.ngk.com/glossary/8/spark-plug/D but I'm not sure it will fit the Subie engines since it reaches in further into the cylinder and may cause interference with the piston.

[DrD123]

definitely no need to lift the engine! The #4 coil on the drivers side can be a challenge - you need to rotate it 180 degrees then wiggle it around a bunch to find the path it comes out. Disconnect the coils before you try removing them. Also - be mindful of the AC line that runs through there - mine has a ding in it now :-(

[abakja1]

I have changed plugs on my 05 lgt, 05 Sti, 05 forester XT and I lifted the engine for all of them so the socket would clear the frame going in and out. this required listening and taking off the motor mount bolts, radiator support bracket off to provide clearance.

 

On the 2011 lgt, you take the front porch mount nuts off as there are 2 to provide clearance.

 

Some of you can do this without lifting the motor, but for me, I have big hands and little patience. Lifting the motor provides ease of swapping the rear plugs in both sides without the swearing.ir cutting up of your hands. Iike to.out the car.in.stands.too so I don't stress my lower back.

[FLlegacy]

I have changed plugs on my 05 lgt, 05 Sti, 05 forester XT and I lifted the engine for all of them so the socket would clear the frame going in and out. this required listening and taking off the motor mount bolts, radiator support bracket off to provide clearance.

 

On the 2011 lgt, you take the front porch mount nuts off as there are 2 to provide clearance.

 

Some of you can do this without lifting the motor, but for me, I have big hands and little patience. Lifting the motor provides ease of swapping the rear plugs in both sides without the swearing.ir cutting up of your hands. Iike to.out the car.in.stands.too so I don't stress my lower back.

 

I use a short wobble extension, my hands are hardly small, but I do have a lot of patience, .

[ripstik]

I use a short wobble extension, my hands are hardly small, but I do have a lot of patience, .

 

i used a 1/4" drive ratchet, that made it much easier. i also used a short extension then switched to a long socket that fit over the back of the spark plug socket. took a bit for me to get my order of operations down, going to remove the ratchet or extension and realizing i didn't have enough room to do so and have to thread in a couple turn, but now that i have that down it's really not the worst job. one last tip would be when removing the coil pack you want to twist it 180 as your removing it, not before, and same for putting it back in.

[TeeMuumi]

Created the account just to give my thanks to Kenpachi as that quote from shop manual was the best advice I could find anywhere. Thanks a lot!

 

For some reason there's quite a lot of different and propably misleading tips on this job so here's what I experienced on fifth gen GT with EJ255 (2010 JDM, although spark plug related it should be the same on US and Europe versions)

All you need to do was to follow the shop manual quoted by Kenpachi so NO lifting the engine is required and also no need to remove the coil connectors although it is easier when they are not tangling on the way. Also the harness clips of the coils comes off merely prying them out with a flat head screwdriver as they are plastic trimm clip inserts and since they are thight around the wire there's a risk to cut the insulation when cutting the clips. You have enough space for the socket extensions when you have removed the battery and the air cleaner box out of the way, you just need to have some patience and finger agility to install the socket and joint extension separately for the #3 and #4 plugs. After removing the air box it should be noted that the intake hose goes straight down the TC so the hose should be plugged with a rag or something similar to avoid anything dropping down to the intake. For the socket extensions I would recommend approximately 10" or 25cm length and two extensions to make it easier. Since you need to use the joint/swivel extension I would recommend to wiggle the ratchet when unscrewing to avoid any jamming of the socket or joint which could lead to breaking something. And when installing the plugs a torque wrench should be used to make sure of the correct thightness as the feel of the wrench is different with joint extension. Last thing worth noting is that my hands are somewhat small, glovesize 8 and the space around #3 and #4 was tight for me also so I wouldn't recommend this job if you have hand size above 9.

 

To give a short guide, here's what I did:

 

- Remove the battery, 10mm nuts on connectors and bracket.

- Remove the air filter box, 2x 10mm nuts, 8mm hose clamp and maf connector.

-- seal the intake hose with a rag or something similar.

- Unscrew the 12mm bolts holding the coil packs, pry the plastic trim clip out.

- Pull the coils out, #3 and #4 you have to turn the pack approximately 180deg due to the L shape of the bracket for the 12mm bolts and tight space further back.

- Insert the spark plug socket together with the joint extension first for the #3 and #4 plugs then it's easier to plug in the extension(s) (of course this depens on the tools you have)

- Install plugs with socket and joint extension screwing them by hand and tightening them with a torque wrench.

- Install all back in (don't forget the rag!)

 

The plugs according to the JDM service manual are as follows:

2.5i SIFR6A11 gap: 1.0-1.1 mm

2.5GT SILFR6B8 gap 0.7-0.8 mm

3.6R SILFR6C11 gap 1.0-1.1 mm

Replacement interval 100.000km (if I read it correctly)

 

I used ILFR6B8 which doesn't have the projected square tip electrode as the SILFR6B8 but they seem to work just fine.

 

I guess that's it. As a disclaimer these are just my experiences and tips, not necessarily suitable for your situation.

Cheers!

[mjb]

Looking for help on the "spark plug replacement" thread. 

Just replaced the 1 & 3 plugs on my 2011 Legacy GT.  Did not get to the 2/4 plugs due to time.

Car only has 69,000 miles.  I think this is the first time they've been replaced.

Used NGK OE plugs.  Coil packs looked good.  Didn't even unplug them to move them aside, just swapped the plugs and put everything back.

Immediate rough idle and obvious misfire when I started the car.  After a minute or two, the check engine light finally came on and showed P301 and P303 (misfire on cylinders 1/3).

Any ideas for troubleshooting?  Seems like the coil packs are rarely the issue, and the car was running 100% fine prior to changing the plugs.  Is it possible that just changing one side caused an issue when they are all the same OE spark plugs?

[DrD123]

So first question with NGK plugs is where did you get them - there are lots of counterfeit ones around.  Second - if you put the original plugs back in, does the problem go away?  If the coil packs are installed correctly (I'd remove and plug them back in - I unplugged mine before removing each coilpack to get it out of the way, and to apply a little silicone dielectric grease inside the boot before reinstalling) and nothing else changed, I'd suspect the plugs as being the issue - particularly if you swap the old ones in and they work fine.

Edited December 31, 2023 by DrD123

[mjb]

Got the NGK plugs direct from NGK. The order was fulfilled by "sparkplugs.com" but I ordered from the NGK website.  They came in original packaging, full price, no indication of counterfeit.  

I pulled the new plugs and tested continuity and resistance.  4.6K-4.9K ohms between terminal and center electrode (NGK says it should be 5K). I then tested the two unused plugs in the box - hovering between 4.7K-5.1K.  I then tested the old plugs (12 years old at this point).  The best read I could get on both of them was 3.4k-3.6K.  I checked for continuity between terminal and hex and outside electrode - none. Same with old plugs.  I checked the gap on all 6 plugs (new and the two old ones that are now out).  All the same.

i.e. - seems the new plugs are fine, not cracked or out of spec.

I then put the old plugs back in and gave it a try.  It took about 5 seconds to start. (five seconds holding the key in the start position).  But when it started, it immediately ran smooth with no codes.

I think the issue genuinely is caused by only replacing two of the plugs.

Had I replaced all four plugs, I would have pulled the battery and had it out long enough for the ECU to "reset".  This would have resulted in a difficult/rough start and made the engine search for idle again, but that happens every time you pull or replace the battery.  In my old 5MT Outback, it would routinely rough idle, lack power, and even die when you stopped for the first 5-10 minutes after pulling or replacing the battery.  Subaur says this is normal for the ECU to reprogram/adjust.

I think just doing two plugs, with two new and two 12-year-old plugs may have been too much for the ECU to compensate or "adjust" one side compared the other.

The real answer will come when I replace all four plugs with the new ones.  Will be back when I've done that.

[DrD123]

I wouldn't think an imbalance at the plug level would cause an issue for resistance, but perhaps it does!  Will be interesting to see what happens when you swap out all 4!  (the rear one on the drivers side is the annoying one when it comes to fishing out the coil pack)

[mjb]

Update.

I replaced all four plugs at the same time and it went exactly as you'd anticipate.  The process itself is a pain, but after completed it started right up and ran smooth.

Learned - replacing just two plugs can cause serious issues, including misfires on the "new plug" cylinders.  Idk how often this has ever come up, but it can now be said  - replace all four plugs at the same time. 

Takeaway - replace plugs at recommended interval.  There is a big enough difference between old and new plugs that the vehicle struggles to run when you mix them.