Ej208D Stuttering on acceleration

[A4RC]

So I bought a second hand 2001 Legacy B4 RSK (RevD) and it looked great, ran very well and a JDM specific shop said it had no issues after an inspection. Now that it is the summer, I have decided to drive it hard and have run into some stuttering during acceleration. No check engine light or sound is made it just jerks a bit. No it is not during shifts, although I'm fairly new to manual and my shifts aren't quick, problem only happens in gear. I read that these cars should be on 100 octane but here in Alberta, Canada we only have 94 Octane. I have been using 91 Octane so far and I will try out 94 next time I fill up to see if that's the problem. I don't know how much boost the twin turbo set up should be making but so far I've found the primary makes 5-10 psi at most and the secondary makes 8-10. However the boost gauge looks shitty and I'm not sure to trust it (It was installed when I bought the car). I'm really lost on what to do since I can't find any similar situation on any forums. Engine is 99.9% stock just with a after-market intake pipe and a cat delete. I will tag a video of a first and second gear pull if you listen closely you can hear the revs stutter(@11-13secs), problem is in all gears and gets worse with more throttle. 

 

 

[doublechaz]

Never run a lower octane gas in a turbo engine than it is spec'd for.

From a few seconds of search I see that Japanese 98 octane rating is equal to Canadian 94 octane rating, so the car requires at minimum Canadian 94.

Running less than rated octane in a turbo engine can pretty quickly blow up the engine.  Fill with 94 right now, stay out of the throttle until you have burned through all of that and filled with just 94 again.  Better yet drain out all the gas and replace with 94, but I realize that is a pretty tall ask, so go the first path.

 

If you don't have coolant in your oil or oil in your coolant, then you are lucky the ECU pulled a lot of timing to avert the worst of the detonation (causing the stutter you describe) and running the correct gas will take care of things.  If your coolant or oil are contaminated you've blown the head gasket and will have to rebuild the engine.

 

edit:

At this point I would watch the oil and coolant like a hawk at literally every drive cycle for the next 500 to 1000 miles as a small crossover leak can destroy the engine bearings weeks from now if the only check you do is after reading this.

Edited May 25 by doublechaz

[A4RC]

I talked with the previous owner and he said the car was retuned for Canadian gas upon arrival, he used 87 all the time and was making 12 psi of boost. ill fill up on 94 next time and ill use a octane booster for now but I believe it maybe a boost leak

Edited May 25 by A4RC

[doublechaz]

If the ECU is detuned to run on lower gas I would use some computer tools to verify that this is the case and if so rock on or put it back to factory and fuel appropriately.  After all, any ECU tune is not going to change the actual compression ratio so there is minimal susceptibility to detonation that can be achieved that way.

I don't know specifically about the 208d vs other engines, but I wouldn't run a turbo anything on 87, but I am thinking about US 87 when you say that.  YMMV.  Some credible info from the tuner who turned down this engine would go a long way toward not sounding so scary.

I can see a boost leak giving a big reduction in power and if the leak is sorta farting it out it might even shudder when it does it.  The boost numbers you give are about the amount below the prior owners stated numbers to indicate a big boost leak, so at least that part is lining up...

Anyway, I'm a big proponent of taking actual measurements of engine data and working from solid scientific principles rather than "trust me bro".

[A4RC]

Yea I agree that I’d rather have actual evidence than just “trust me” so I am going to run 94 in the future. The only reason I used 91 rather than 94 was because I didn’t even know it was available until I already paid for a full tank of 91. I plan to tune the engine properly but as of now I do not have the money for that. My next purchase will be a completely new vac hose  kit to replace the 20+yo lines it currently has

Edited May 25 by A4RC

[silverton]

Even if it was tuned for it I'd never run less than premium in a turbo engine.

Is the stuttering occurring at the turbo transition point? afaik, the turbos never work together or at the very least overlap is very short. reviews of these cars at the time were never favorable as the transition while driving it hard through the corners was unpredictable.

Edited May 25 by silverton

[A4RC]

Stutter occurs when ever a certain amount of throttle is applied. Can be low rpms or high rpms but generally occurs when I give it more throttle. I’ve tried to see if throttle control fixes the problem however even with very light and gradual application of throttle the stutter happens when 50-60% open. The severity of the stutter depends on how open the throttle is. I’ve seen pedal cam footage of pros driving the same car and they have no problem flooring it but when I try to do the same the car hiccups like I mentioned.  Also the turbo transition point (VoD) has been hugely minimized in the RevD Ej208 to the point many say they don’t notice it so I don’t believe that’s the issue

[doublechaz]

Sounds more and more like boost leak as you mention different details.  I think you are on the right path to getting to the bottom of this.

[A4RC]

I guess a update is needed, the vac hoses had already been replaced with an autobahn 88 kit and I checked the lines more thoroughly for any cracks and leaks but none where found. I found another post with a insanely similar problem that ended up being a fuel pump unable to keep up with high rpm. I replaced my oem fuel pump assembly with a non-oem one I found since my fuel gauge is not working properly but both the stutter and faulty gauge are still present. Once I do a check with a multimeter on the oem fuel pump assembly, Ill replace the pump with a 340lph kemso pump. Ill post my findings here

[Cabbages]

Any luck yet? assuming the gas didn't fix it, a few thoughts...

 

Were the restrictor pills in the vac hoses replaced as well?

Is the primary downpipe decatted?

would also be looking for leaks on the plastic intake under manifold .(extra unmetered air) or around intercooler, they get rather brittle and those ribs don't move like they used to

 

fuel guage issue could be the level sensors in the tank, afaik there are 2 of them, 1 for each side since the fuel tank is saddled over driveshaft. Have a simililar issue with my guage - tends to work more consistently with over half a tank and barely works while under 1/4.

 

 

[A4RC]

New pump installed - nothing changed, bought a brand maf sensor (Denso 604, yes it was real and not a fake) - improved throttle response and low rpm drivability but still stumbles when boost is made. I’m not too bummed out about the unneeded replacements since it is preventative maintenance but this problem still bothers me even if the car runs fine under normal conditions.

Fuel gauge wise I have the same issue where it gets much more inaccurate the less fuel is in the tank. Anywhere above 3/4 full it very rarely drops but still occasionally will read empty (especially after parked for long) I’m guessing the other sensor would be under the left rear passenger seat?