SF5 Hesitation

[creed]

Hi everyone. I've haven't owned a Subaru for a couple years, but just got an '01 SF5 STi out of Japan.

Driving it back from Vancouver last week right away I noticed a sputter/hesitation under load. As I'd roll into the throttle and the boost would build, it would start to buck pretty bad.I basically babied it all the way back to Saskatoon, as I could mostly avoid the problem if I was really gentle with it. So far I've done a Seafoam treatment in the fuel, and changed the fuel filter. Neither have eliminated the problem. I've had someone tell me it could be the fuel pressure regulator, that was going to be next on my list.

Thoughts?

[jdmvip]

Hey creed welcome to the forums sorry to hear about the issues. Could you make a new thread with pics of the SF5? Is this the EJ20G or EJ205 that is in yours? I am not sure in the SF5 when they switched over but am guessing yours probably has the EJ205.

I would start with the basics such as inspecting coil packs and spark plugs. Clean out your MAF and Airfilter.
If possible try and check for codes as well.

Also take a quick inspection of the hoses spray something non-flammable or even misted air all around the intake and any hoses and see if something gets sucked in (it could be something as simple as that).

Beyond the basics I would take it to a good mechanic for diagnosis.

[creed]

I will definitely do up a proper intro thread for the car, and thanks for the ideas. I'm fairly mechanically inclined but I have to get used to a foreign car again haha.. I think I'm more afraid to dig into it for fear of breaking something that's hard to source!

BTW my car has the EJ205. I tried to read codes with my OBDII code reader, but when I plugged it in it wouldn't connect to the computer. Is there a trick to this on JDM cars or a certain reader that's required? The CEL is not on.

I will clean out the MAF and check the air filter and have a look at the ignition system. You're right it could even be a leaky hose.

I noticed last night that when it hesitates or "sputters" I can feel the kick through the throttle linkage....I wonder if this could actually be a backfire thru the intake??

I'm currently out of town on a work trip so I can only ponder and plan at this point

[jdmvip]

Thanks creed looking forward to it. I'm currently considering an SG5 Forester XT. I am not quite sure what you need for the JDM EJ205 but a lot of JDMs in general are not OBDII compatible even if they have the connector. If you're still having trouble I'll see what I can find.

I'm sure hoping it's a fairly simple issue but the above are some basic things that can happen to the EJ platform commonly in my experience. Another possibility is that your BCS is bad or dirty.

Another easy thing to check and replace is usually the Crank Sensor, it was bad on my EJ20G and made a world of difference (cleaning helped but a quick replacement made the engine run incredibly more smooth).

[creed]

So I replaced the crank sensor and unfortunately that didn't help. Today I finally tracked down my fuel pressure gauge and hooked it up along with a vacuum/boost gauge to see whats up. Started the car and at idle I had 15 inHg or 7.5 psi vacuum and 40 psi fuel pressure. Seems a bit high right? Here is a short video I uploaded to youtube. I was in Drive, holding the brakes and applying throttle steady at ~75%. Thoughts?
https://www.youtube.com/watch?v=01UwOM99sy4

[creed]

Something I forgot to do the first time I had the fuel pressure gauge hooked up was to pull the vacuum line off the fuel pressure regulator and watch for an increase in pressure. So I hooked it up again and sure enough the pressure increased by exactly 7.5 psi (which is the vacuum pressure at idle). This is the main FPR test right? It seems that the FPR is functioning correctly.

I pulled out the cam position sensor and did a resistance check across it (just in case) - it checked out.

I'm zeroing in on the coil now. I checked both secondary windings and the resistance is within spec. But I believe the primary windings can't be checked on this style of coil (4 pin connector). I clamped a timing light over each plug wire and watched for steady flashes as i revved the engine. I THINK I noticed some gaps in the flash pattern on a couple cylinders. The inductive style timing light is a bit finicky so I didnt want to jump to conclusions...but I was able to replicate the results several times.

[jdmvip]

It's very possible your coils are bad the tricky thing about checking resistance is that it could be a completely different story while you're on boost.
Have you sprayed some misted water or similar to see if you have any air leaks?

Hopefully you're just one step away from sorting this out!

[creed]

FIXED!

It was the spark plugs. Eroded and like 0.080 gap. I'd have never expected plugs to cause such a major stumble. But these were no ordinary plugs! A fresh set fixed it right up. Thanks for the help jdmvip!

[jdmvip]

Awesome creed I'm glad it was something that simple! How many K's does your Forester have maybe they are original plugs?!

[Vancouver98STi]

FIXED! It was the spark plugs.

Heh heh... why check the simplest things first?