HELP !! -- Misfires with APR Stage 2

Hi Guys,

So I am APR stage 2. Had NO misfires before I went stage 2. Now I cant get rid of them. CELs are for all 4 cylinders plus a random misfire code also.

Here is what I have done trying to correct the issue...

2 Sea foam treatments

Pulled intake manifold and did full carbon cleaning. (car had 59K) Definitely needed this. Valves looked great when I put her back together.

New Intake manifold gasket

Cleaned each individual fuel injector and put new seal kit.

New R8 coil packs (Already had a set installed, but from previous owner so I bought a brand new set and installed.)

Tried NGK BKR7EIX plugs

Tried Bosch Double Plat. FR6KPP332S plugs

Tried NGK BKR8EIX plugs gapped at .024 (recommended by GMP Performance Tuning Shop who did the stage 2 tune.)


Car will not stop misfire/ hesitation issue, but it happens at random. Runs good for a day, then runs like crap w/ heavy misfires and throttle hesitation, then back to good again. Car is running extremely rich it seems. Under very light acceleration it is registering 6-9 mpgs on the display screen where you can track this. Car is basically pouring on the fuel and not able to burn it all because the AFR is so rich I think.

Bad MAP or MAF sensor? Any ideas or experience with this? Its driving me crazy!

The one thing that sticks out that I don't see mentioned is the PCV valve.

Jspeed said:

Tried NGK BKR8EIX plugs gapped at .024 (recommended by GMP Performance Tuning Shop who did the stage 2 tune.)

Click to expand...

Not the right plugs or gap for Stage 2, btw

Were you stock before stage 2, or at stage 1? If you were bone stock, you may be getting massive boost leaks which would make the car run like shit. Also, try the plugs at 0.028" as that's what APR recommend over the stock 0.032" IIRC.

Went from stock straight to stage 2. Running a CTS catch can setup also. I wanted to eliminate the pcv so it couldn't be an issue. I did try gapping factory Ngk bkr7eix plugs at .028.

No luck no matter the plug or the gap it seems. Any other ideas?

I will check for a boost leak. Installing gauge this week. What psi should I see at stage 2 ?

Been dealing with misfires ever since I got the 2.1 (not current 2.4) tune. Zero misfires previously with stage 2 1.? tune. Tried everything you've done also so look forward to seeing if you get any results here.

do you have O2 spacers on there>? if you have the sensors screwed too far out of the stream it will overcorrect by dumping as much fuel as possible and youll get too rich issues and misfires. i tried everything to figure what this exact issue was and that finally fixed it. PCV and N75 didnt.

I dont think there are any o2 spacers. I will pull the sensor today and give it a look and a good cleaning.

Didn't think about that. Wonder if it could be covered in carbon and not reading correctly? My valves were terrible when I pulled the intake manifold.

Unplug the MAF sensor to see if the car runs normal. CEL will still stay on of course. If it does, replace the sensor. Buy it on Ebay for a lot less than anywhere. It will come complete with the housing.

Did you install the catchcan at the same time? I would remove that for testing.

Did you change the PCV valve yet?

Sounds like a vacuum leak.

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Car running the same before and after the catch can install. It has had no effect positive or negative it seems.

Check all seals. Do you have a boost gauge?

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Is it possible you have something wrong with your catch can or PCV system? When my PCV failed i was getting horrible gas mileage, smoking like crazy, and misfire codes.