I recently purchased a 2013 Sonic RS 1.4t 6spd with about 82,000 miles. When I bought it it was broken - every code under the sun, but main symptom was screaming through the crank seal at idle/vacuum.
I put a new GM valve cover on it, and did the Cruzekits PCV fix (the intake plunger was gone) and the car ran great and the only code it had was P0420 for cat efficiency, but my LTFT's were constantly creeping to -30 at idle - but didn't seem to to affect driveability.
After driving a few days, the P0420 went away and off the "permanent codes" list, and to my surprise, I don't get any fuel mixture or intake performance codes, even though my LTFT's are skewed WAAAY rich any time I'm idling.
The car has always been slow, but I'm used to a 500hp car - so I just figured it was a 138hp car and that was that until I got an OBD2 display so i could watch boost and coolant temps. I thought it was odd that the car would only make 8-9psi when I googled and it said stock boost was 10-15psi. After a few WOT pulls, it started making less boost until it would only make 3psi and threw the P0299 underboost code. This is the testing I have done so far:
1) Smoke tested the intake, no leaks. Intake tube removed and smoke machine rubber cone inserted at the turbo inlet. After a good 5 minutes of the smoke machine running, I pulled the Evap connector on the intake manifold to verify the smoke got past the throttle and all, and it popped off with a bit of positive pressure followed by a ton of smoke - so the machine was working and I have ZERO intake leaks.
2) MAF reads 2.2-2.4g/s at warm idle with no accessories (normal from what I google).
3) Pressure tested wastegate - pumped up to 15psi and it held positive pressure without bleeding off. Wastegate arm moves smoothly through what I think is the full motion.
4) Set wastegate preload to 2 full turns tighter than even fitment with pin.
5) Pressure tested bypass valve to 15psi and it held vacuum pressure with no leaks - can hear it close when releasing vacuum pressure.
6) Smoke tested vacuum line from bypass valve to under intake manifold - no leaks.
7) Pressure tested Evap Purge valve and no pressure gets through when pressurized to 15psi on the intake side, and no vacuum bleeds down when vacuumed to 15in on the tank side - appears to be working normally (but I ordered a new one anyway, since the OEM valve is only $35).
8) Compression tested the engine - 185-195psi in all four cylinders (good).
9) Disconnected the wastegate vacuum hose. THIS IS WHERE IT GETS WEIRD. The first few pulls I cautiously made, it boosted normally - I let out when it hit 13psi for fear of overboosting too much. After several more tries, the boost started to come down. After the 7th or 8th try, even at WOT in 5th (so boost would build slowly and I could get out of it), it would only make 5.5psi at WOT, even to redline. The BPV sounds louder when I let off... not sure if it's in my mind, but if the intake is only seeing 5.5psi, it sounded like more out of the BPV.
10) Scanned car after wastegate line removed - no active codes but a pending "overboost" code was there. Car never went over 13psi the whole time, but could be the OBD display was a little laggy. FWIW I'm running 93 octane fuel.
So I'm open to suggestions. I feel like the only things it could be are:
1) Large cracks in the turbine housing
2) Damage to turbine/compressor wheels (though that wouldn't explain why it boosts higher at first, and then gets lower and lower with more pulls)
3) Exhaust restriction - this one is strange because the cat could be dead, chemically, from all the oil/fuel that passed through it from the previous PCV failure (I don't know how long the previous owner drove it like this), but the backpressure test told me that it's not clogged or plugging the air pathway...
4) Something that leaks internally in the intake manifold to someplace else in the engine that's not external.
Could an internal leak in the BPV solenoid cause something like this?
And I still have no explanation for my crazy rich (-30) LTFT after long idle periods. The sad thing is i think the PO chased this because it has Chinese MAF and O2 sensors - but my OBD Fusion datalogs show the MAF idle voltage normal, and the upstream O2 cycling like it should. The rear O2 acts weird, but I'm not sure that could have any affect on boost pressure or idle fuel trims.
Please help
I put a new GM valve cover on it, and did the Cruzekits PCV fix (the intake plunger was gone) and the car ran great and the only code it had was P0420 for cat efficiency, but my LTFT's were constantly creeping to -30 at idle - but didn't seem to to affect driveability.
After driving a few days, the P0420 went away and off the "permanent codes" list, and to my surprise, I don't get any fuel mixture or intake performance codes, even though my LTFT's are skewed WAAAY rich any time I'm idling.
The car has always been slow, but I'm used to a 500hp car - so I just figured it was a 138hp car and that was that until I got an OBD2 display so i could watch boost and coolant temps. I thought it was odd that the car would only make 8-9psi when I googled and it said stock boost was 10-15psi. After a few WOT pulls, it started making less boost until it would only make 3psi and threw the P0299 underboost code. This is the testing I have done so far:
1) Smoke tested the intake, no leaks. Intake tube removed and smoke machine rubber cone inserted at the turbo inlet. After a good 5 minutes of the smoke machine running, I pulled the Evap connector on the intake manifold to verify the smoke got past the throttle and all, and it popped off with a bit of positive pressure followed by a ton of smoke - so the machine was working and I have ZERO intake leaks.
2) MAF reads 2.2-2.4g/s at warm idle with no accessories (normal from what I google).
3) Pressure tested wastegate - pumped up to 15psi and it held positive pressure without bleeding off. Wastegate arm moves smoothly through what I think is the full motion.
4) Set wastegate preload to 2 full turns tighter than even fitment with pin.
5) Pressure tested bypass valve to 15psi and it held vacuum pressure with no leaks - can hear it close when releasing vacuum pressure.
6) Smoke tested vacuum line from bypass valve to under intake manifold - no leaks.
7) Pressure tested Evap Purge valve and no pressure gets through when pressurized to 15psi on the intake side, and no vacuum bleeds down when vacuumed to 15in on the tank side - appears to be working normally (but I ordered a new one anyway, since the OEM valve is only $35).
8) Compression tested the engine - 185-195psi in all four cylinders (good).
9) Disconnected the wastegate vacuum hose. THIS IS WHERE IT GETS WEIRD. The first few pulls I cautiously made, it boosted normally - I let out when it hit 13psi for fear of overboosting too much. After several more tries, the boost started to come down. After the 7th or 8th try, even at WOT in 5th (so boost would build slowly and I could get out of it), it would only make 5.5psi at WOT, even to redline. The BPV sounds louder when I let off... not sure if it's in my mind, but if the intake is only seeing 5.5psi, it sounded like more out of the BPV.
10) Scanned car after wastegate line removed - no active codes but a pending "overboost" code was there. Car never went over 13psi the whole time, but could be the OBD display was a little laggy. FWIW I'm running 93 octane fuel.
So I'm open to suggestions. I feel like the only things it could be are:
1) Large cracks in the turbine housing
2) Damage to turbine/compressor wheels (though that wouldn't explain why it boosts higher at first, and then gets lower and lower with more pulls)
3) Exhaust restriction - this one is strange because the cat could be dead, chemically, from all the oil/fuel that passed through it from the previous PCV failure (I don't know how long the previous owner drove it like this), but the backpressure test told me that it's not clogged or plugging the air pathway...
4) Something that leaks internally in the intake manifold to someplace else in the engine that's not external.
Could an internal leak in the BPV solenoid cause something like this?
And I still have no explanation for my crazy rich (-30) LTFT after long idle periods. The sad thing is i think the PO chased this because it has Chinese MAF and O2 sensors - but my OBD Fusion datalogs show the MAF idle voltage normal, and the upstream O2 cycling like it should. The rear O2 acts weird, but I'm not sure that could have any affect on boost pressure or idle fuel trims.
Please help
