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You called it:
P0234 - overboost
P0455 - evap leak large
P1250 - boost deviation
Since it's cheap and 18 years old now, I'll just order a new N75 valve and inspect all the vacuum lines while I'm at it. The diverter valves and wastegates are newer, so I'm assuming it's not an issue with those.
As for the evap leak code, the previous owner was chasing that issue also. The car already has a new gas cap. I guess I'll check the valve on the charcoal canister, I hear those like to freeze up.
New N75 installed. The P1250 and P0234 codes are back (but no CEL).
Time to go boost leak hunting...
Also, another weird issue that has popped up a couple times:
While at freeway+ speeds, usually around when the spoiler would go up, the dash yells at me that there is a PSM failure and the ABS light comes on. When I turn off the car and restart it, the warning is gone and there are no codes. The wing hydraulics have been removed and the car has a GT2 harness in the deck lid. I guess this is another reason to get access to a PIWIS so I can make sure the hydraulic wing is properly coded out.
Regarding the overboost, check the line going from the N75 to the wastegate actuators for leaks. Most commonly, the rubber hose near the actuators gets baked from the exhaust heat and rots away right at the clamp. I've also seen the plastic line from the N75 to the tee above the plenum get a hole in it from rubbing on the A/C compressor. Either way, the wastegates open by pressure being applied to them, and if there's a hole in the line feeding them that control pressure will escape and the wastegates won't open.
If the car is running aftermarket wastegates (usually noted by an S-shaped rod with a coupling nut between the actuator and the wastegate flapper arm, but can also be an OEM straight rod actuator that has been cut open and resealed using a circular ring around the air can), make sure the rods aren't bound up and use a Mityvac or similar to make sure both sides crack open at the same pressure, should be less than 1bar. The actuators should hold pressure reasonably well with a slow bleed down, though they often won't hold vacuum at all.
When I replaced the N75 I carefully inspected all the lines associated with it as far as I could trace them, at least on the top of the engine. I'll crawl under there this weekend and check starting at the wastegates. The wastegates are aftermarket 1-bar units and they were "synched" when installed. Definitely wouldn't hurt to check them though.
Regarding the overboost, check the line going from the N75 to the wastegate actuators for leaks. Most commonly, the rubber hose near the actuators gets baked from the exhaust heat and rots away right at the clamp. I've also seen the plastic line from the N75 to the tee above the plenum get a hole in it from rubbing on the A/C compressor.
I spent some time under the car this weekend inspecting all the pipes and hoses I could get my hands or eyes on. Everything looks and feels good. I didn't have enough time to do a proper leak test though. It was quite awhile ago calendar-wise, but not very long ago mileage-wise that the car had a clean leak test. I still plan to do one soon though.
Assuming I have no boost leaks, what are some other things that could be causing this? My current theory is a sub-par tune. Judging by the exhaust tips and my fuel mileage, the car seems to be running pretty rich.
Last edited by Capt. Obvious; 08-20-2019 at 12:45 PM.
Unless you drop the motor some and remove the Y pipe, you can't see many of the hoses that'll have leaks in them. I found this one only by removing the Y pipe entirely. You're probably running rich because you have boost leaks.
I didn't have enough time to do a proper leak test though. It was quite awhile ago calendar-wise, but not very long ago mileage-wise that the car had a clean leak test. I still plan to do one soon though.
Boost leak tests are very quick and easy once you know how (and you build or buy the right test plugs). Apart from getting the car up on a lift, ramps, or jack-stands for a bit more clearance, perhaps 15-30 minutes to confirm if you are holding pressure? Just pull both lower intercooler hoses which are easily accessible, plug one, pressureize the other, listen for leaks and see how long it holds pressure.
Finding the leaks if you are not holding pressure: Some are obvious and easy, others not so much.
Fixing the leaks: Ranges from not bad to total PITA (#16 check valve).
Still dealing with that overboost code, but I've been too busy with other projects and commitments to do anything about it. I need to go to the hardware store and buy parts for a pressure tester. Maybe this weekend.
I did have time to swap out my GT2 wing for an OEM wing though. I just prefer the small wing look. If anyone is interested in buying the GT2 spoiler, shoot me a message. I'd prefer a local sale, but I can ship if need be.
The spoiler is black, but it's hardly noticeable against the Lapis, so I'll just sport it as-is for now and get it painted this winter when I have a handful of other small items done.
Not much new with the car, just been driving it and collecting parts for this winter.
Does anyone know if the carpet from a Cabrio will work in a coupe? There are different part numbers, but when comparing them in pictures it looks like the only difference is in an area under the center console which wouldn't matter anyway. I'm currently searching for black carpet to replace the beige and there seems to be a lot more Cabrio carpets available than coupe.
Also, I'd like to go back to a more OEM looking engine compartment, so if anyone has a factory airbox they'd like to sell, shoot me a PM. I'd be happy to work out some kind of trade for my Evolution V-flow as well.
08-09-2019, 12:58 PM
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