Car: 2004 Subaru STI Mods: full exhaust, MAPerformance EF2 turbo, injector dynamics 1000cc top feed conversion injectors, grimmspeed ebcs, fuel lab fpr, Perrin cai, Walbro 255 fuel pump, one step colder spark plugs. Problem description: This problem started immediately after installing both the MAPerformance EF2 turbo and the ID top feed 1000cc injectors. The motor accelerates smoothly from idle up to about 2600 rpm, from about 2700 to about 2950 rpm my motor will stutter/ hesitate sometimes pretty violently, after that rpm range it is smooth at wot and partial throttle all the way to redline under boost. I've also noticed that if I accelerate through this rpm range regularly that I am losing about a quart of oil every 500 miles or so and if I shift before or downshift so that I am above the rpm range I do not lose oil at all. This seems to be happening only under load, when the car is not under load the motor is smooth all the way through the entire rpm range. The car was tuned by nuke and didn't have this issue before installing the turbo and injectors. Please help!! I have done a lot to try and diagnose the problem and nuke has already ruled out a few potential culprit. Avcs. Front o2. Maf. Maf scaling. Avcs tune.throttle body. If anyone has anything to suggest I try I'd be more than willing to give it a shot.
Ugh that does not sound fun. bad turbo seals? Bad PCV valve? Turbo oil drain not working right? Hope someone smarter than me can pitch in
It's not fun at all. Turbo was rebuilt by MAP after I bought it brand new, installed it, and found out the oil seals WERE bad so the turbo seals are good. I think if the turbo drain were bad the hesitation would have been there with the stock turbo but it wasn't so I really don't know on that, how could I check? I ran sea foam through the vacuum system to clean the pcv valve so I don't think its that either. I'm wondering if the bigger turbo is causing too much oil pressure and causing blow by/ hesitation. I think I'm going to have my stock turbo rebuilt and installed with the injectors to rule out injectors being an issue and possibly narrowing it down to the turbo.
Myself I'd probably take the 30 minutes to pull the PCV valve and truly verify that it's working properly before moving on to more extreme measures, but it's your car/life
Well at least that's one thing you can cross off the suspect list, which is good but not as good as if it had fixed it. What about making an appointment with MAP to have their techs check it over? You dropped a chunk of change on the turbo, I'd hope they would stand behind their product and help you figure out the issue. Even if they charge you diagnostic fees that would probably be reasonable; they may have already rebuit the turbo but sometimes you need to troubleshoot the turbo&car as a system... I wonder if the hesitation and oil consumption are two separate issues, and need to be attacked that way. It almost sounds to me like a fuel system resonance issue. Did you do a series or parallel setup with the fuel rails? Still have the OEM fuel dampner in place? Can you post a picture of the fueling system install/layout?
I like to think its usually the simplest solution. You stated that the issues started as soon as the turbo was installed... sounds like the turbo. If your turbo is not working correctly, those issues will occur. It might be easiest to pull the turbo again and see if there is evidence of continued failure. Another question, it may be stupid but its a good clarification. Did you have the car tuned after injectors and turbo were installed? I assume yes because NF did the work.
Well I actually have a friend that works at MAP which is why I bought the turbo in the first place so I'm hoping I'll be able to work something out with them, problem is I recently moved to California and I have the car with me. Driving the car down here with me I noticed that it really only lost oil when I would accelerate or cruise in that rpm range. It wouldn't lose oil if I avoided that rpm range all together so I'm assuming the loss of oil and the hesitation are correlated but I'm not 100%. I have thought about changing the layout of the fuel system. I want to say I set it up in series but I also could be wrong, I will get out and take some pics when I have some time. Where is the OEM fuel dampener?
Curry, the turbo and injectors were done at the same time and then immediately tuned after install. After some more diagnostics I will be rebuilding and installing the vf39 to see if it's still having the same issues with a different turbo.
Could it be the motor giving up? Have you done a compression test? That's my Noob diagnostic skills idea
I believe the 04 STIs had two dampners, one in the feed line and the other in the return line, like this (in red):
