Misfiring when warm and not hitting peak boost

[Brokelikemycars]

Kind of a long story since it's been happening over the last 3 years and I haven't driven it in a year in a half due to it. Ill list all the mods and what I did to try and resolve the issue and failed. My air compressor went out in my accuair cvt tank so it sat for 2 weeks during covid, accuair went out of business for the time being so I had to order parts to convert my tank to external compressors and waited 2 weeks while stuff was being shipped. Battery died over the 2 weeks it sat, jump started it and didnt have any starting issues since. Once I fixed the issue and started driving it the problems began to appear, random misfires all cylinders, cylinder roughness counted so fast the cel would turn on here and there. Cleaned the MAF. The car overheated twice, never while driving only when I stopped to park it in the garage the gauge climbed. Changed the thermostat, fixed the leak No more overheating. Drove one day and got to park it and it started stumbling at idle, wiggled the maf plug and stumble went away.

Ran fine as long as it didn't hit operating temp, anything below half I could hit full boost without issue. Replaced the MAF, installed OTL coil packs, stock silfr6a plugs gapped to .028, aem 340 pump (dw65 wasn't bad but did it anyways), bosch afr o2 sensor, added a ground from the head to frame (was broken). Was good for a week and problems came back worse than ever. Took it on a trip to the beach and 20 minutes in the car was bogging and shaking like a raped ape unless I coasted and sped up to stay at speed limit. Only codes I was getting at the time were p0301 302 303 304.

New issue appears. Driving the car dosent get full boost until about 3500rpms, anything less than flooring it, right before 3000rpms the car felt like it would pull timing, afr goes lean then boost comes in and afr goes back to 11.2. Swapped the stock FPR to a 06 STI vacuum operated fpr, boost leak test, small leak on turbo elbow and a coupler(fixed), issue still persists.

New code, p0340 pass side cam sensor, rough idle didn't want to start. Bought a new oem and replaced it, car wouldn't start until 10 seconds or more of cranking (code still there). Put the old one back in, started right up and the code is gone. I could feel the car running worse so I parked it. Moved the car recently from my shop to my house with a new battery and it ran great driving 20 minutes home, no misfires but still not hitting peak boost. Went and started the car and now p0345 for the driver side cam sensor, won't stay running without revving. I love this car but I don't want to keep dumping money in it especially if nothing is working lol. Driver side cam sensor will be done soon, thinking about doing intake mani gaskets as well.

 

08 Legacy gt

STOCK LONGBLOCK super old tune on a cobb apv2 cryotuned. 20.8psi 379whp 349wtq on 93 at sea level

YouWish racing ELH
grimmspeed up and catless dp
Perrin catback
38mm tial ewg
Kinugawa TD06SL2-20G 9 blade 8cm
Aem340
Id1000
KStech 73mm maf intake
Perrin turbo Inlet
FMS fmic
GFB hybrid bpv (full recirc)
TGV deletes
3mm phenolic spacers
Grimmspeed 3 port ebcs

[lagwagon]

You said you replaced the MAF but did you replace the MAF plug? I-Wire sells a replacement as it is apparently a failure point. I'm not sure how this could be related to the cam sensor codes without there also being a MAF code though but I'm no mechanic.

[KZJonny]

On 9/9/2023 at 6:37 PM, Brokelikemycars said:

08 Legacy gt

STOCK LONGBLOCK super old tune on a cobb apv2 cryotuned. 20.8psi 379whp 349wtq on 93 at sea level

Curious about this particular point.Given the Caps, I assume stock means stock.

I'm looking at the boost figure and wondering if some of what you are seeing is compression troubles. Stock head bolts are generally agreed to be "good" for only around 17psi, above which you are rollling the dice. Could be 3 years of a 21psi tune has finally come time to pay the piper?

Comparing compression test warm and cold might give you some indication if this is a problem, and while it certainly doesn't explain everything, it might go some way to explaining the over heating?

 

Might mean nothing, but on my engine I've learned to hold back from 'full beans' runs since around 16.5psi I start to get some coolant blowout. Pretty sure this is the heads lifting and allowing a touch of combustion gas into the cooling jackets. I'm all good at ~15.8psi, no coolant issues. These engines aren't getting any newer or tighter with time, and I've only got ~166k kms on mine.

[Brokelikemycars]

@iagwagon I did not replace the plug. Ill look into replacing that too since it gave me trouble once, when it rains hard when I am parked outside and aired down, every once in a while the car won't run and I'll have to unplug the maf to limp it somewhere and it'll start right up when it's dry.. 

@KZjonny I have yet to do a compression/ leakdown test, scared of the results LOL though it would be the best indicator of a good engine. The overheating issue was a leaky lower rad tube which was fixed shortly after. I have however had the headers off the car cause of a crack and seen the exhaust valves to be caked in some white corrosion? Thought it could be leaky or burnt valves but it runs fine at idle cold or warm, only breaking up in boost.

[Brokelikemycars]

P0345 fixed. Sensor was fine, a wire was pulled out assuming from the previous owner since it was extended and just shoved in there without anything holding it in. Getting 18psi now and it dosent pull much timing before getting into boost. Gotta take it on a long drive to see if it misfires but ill save that for when I have time off again.