So my Evo has been sitting in the garage after cooking the clutch in an AutoX race. It's had many years of being run well over stock HP and I wasn't surprised at all. I took it to a favorite shop of mine in the Chicago area (APM Racing) to have the clutch replaced.

I took it home and have been spending the week breaking the clutch in, so all in town, very light easy driving, no full throttle. Well I surpassed my break-in period and wanted to take it to race this weekend.

But I took the car to full throttle and now I've got a nasty misfire. The car runs very well at medium throttle and in town. Just full throttle. I took a video:


#1 on my list is to start hunting for boost leaks.

What else should I look for?

 

I have the exact same problem! Going to try regapping my plugs to see if that helps. I was experiencing this also after a new clutch install and perrin intake.

 

I need to build myself a boost leak tester, but in the meantime I was going to check my plugs too. Planning on following this how-to : https://www.evolutionm.net/forums/ev...er-5-02-a.html

Do you think you fouled your plugs? Kinda funny coincidence that you also did you clutch.

 

I'm using copper plugs so they may be fouled. I bought a new set and gapped them just been too cold to swap them out. Car drives fine during cruise just anything over 80% throttle it misfires.

 

Did you fix your issue? What happened?

Sadly I messed up the tip on one of my plugs. Cheap *** AutoZone gapper, and my lack of finesse.... So I couldn't test that out, ordered 5 more this time to be safe.

Boost leak test. I found a tiny seep on the upper intercooler pipes. Weirdest thing.... The oil fill cap started leaking after a while hooked up to the compressor. Is that a problem?

 

boost leak aint it, need to check plugs and check gap--boost leak will cause a rich issue, you have a lean issue at best and likely just a gap / coil issue.

 

Get one of the blade style gap measuring tools and toss out the ring tool

 

I got a proper blade tool with a end for opening and closing the gap. Worked like a charm, I think. Put in the new plugs and I still have a nasty backfire.

Here are the old plugs...




Placed in the order of the cylinders. <br/>


So the air coming out of the oil fill cap is normal? No worries there?

And I guess I'm on to the wires and coils. Is this the time to consider an upgrade? OEM a better idea? I don't want to need a retune.

 

Going to be a high of 64 today so I will change my plugs and report back. I have them gapped at .020 so we'll see if that helps. I'm using ngk bpr7es. If that doesn't correct the issue I will try the br7es as I think they are half a step colder. I may try the bpr8es before I consider a coil on plug setup.

 

My next items to replace:
Denso 671-4270 Original Equipment Replacement Wires
Denso 671-4280 Coil Over Plug Boots

 

PROBLEM SOLVED. Pulled the old plugs and looks like the shop that installed them used the BKR7E which seemed to be recommended for a subaru. I installed BPR7ES gapped at .020 and did a pull in 3rd gear and it revved smooth to redline.

 

I don't recall any ground straps on the transmission, but just in case, have a look around where the engine and trans mate up for anything unusual. I know some poor engine grounding can cause issues like you have. High ground resistance results in less voltage for jumping the spark plug gap. I really doubt it's your issue, but since the trans was recently out, I'd go ahead and take a look. I really suspect ignition side. If you can get some misfire faults, try swapping coils to see if they track with one of the coils. Problem is, to get faults, you gotta get quite a few misfires.

 

I replaced the coil boots and wires. I have the same misfire problem. I'm going to try a tighter gap.

I just saw this now, I'll peek for the grounding issue. I have yet to get a misfire fault, I've had plenty, or do I need a bunch in a row? See the video. No codes. And all subsequent tests. No codes...

 

I went back to your original post and I couldn't find what spark plugs you are running and what gap?

 

You can take off the oil cap and "adjust" the metal part so it clamps on the cover tighter when you put it on. I also used locktite on the nut inside the cap (paranoia). A bad PCV valve may be the cause for air coming out of the cap.

Try a tighter gap on the plugs and make sure you are using the right ones. Are you on speed density or MAF?
How long has it been sitting? E85 or gasoline?