Well today when I was on the way to work, I noticed that when I go WOT boost builds up, but before it reaches its peak I feel a bit of a slowdown, and then it pushes on to the top. What could that be?

 

The cause could be many things. More information would be helpful.

What year is your car? What performance mods are on your car? Have you made any recent changes to your car? Omit suspension mods for this topic.

How long has your car exhibited this problem? Does it do the same thing in all gears?

When you say 'slowdown', do you mean that the car actually slows down, or do you mean it momentarily doesn't accelerate as hard as the previous few seconds?

Does your boost gauge register a drop in boost when you feel the car having that problem?

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0==WW==0
"…axles of evil…" - george w. bush

 

what rpm. what does boost reach. how much does it fall to?

 

well it's a 02 wrx with a spt catback and accessport. the flat spot happens around 4500 rpm and goes for around 500 rpm before its starts to pull hard again. I haven't noticed the drop in the boost gauge. When I'm at WOT, once I reach 4500-4700 rpm, it feels flat for few seconds. It just started happening two days ago, so I'm thinking maybe something came loose. Thanx for the info!

 

and to answer your other question WW it definitely happens in 2nd and 3rd gear. I havent pushed it in 4th and 5th to 4500 rpm.

 

i guess nobody knows

 

I can suggest checking underhood for loose intake hoses or vacuum lines that have developed a crack or a leak. The fact that your car recovers after a few seconds and still makes decent power at higher rpm hopefully means it isn't anything really serious. Since you haven't made any recent changes and the acceleration flat spot came on rather suddenly, it might be something that can affect fuel metering under boost. Definitely not normal behavior, though.

Other than that, this isn't something that I've encountered locally in friends' cars.

--
0==WW==0
"…axles of evil…" - george w. bush

 

I'm having the same problem. I emailed the shop that did my tuning and they had no idea. For me, it only does it on occasion and always at 6000 RPMs in both 3rd and 4th gear (haven't tried it in fifth gear).

 

Mine used to do this too. Never found a resolution.

 

Mine does the same.... weird. Just like you guys have said before, foot on the floor, boosting as normal then it feels like you have just taken your foot off the gas then stuck it back on again!!

 

could it be the stock turbo? that thing is small and in my 05 wrx, it feels as though it "runs out of steam" past 6k

 

Poor electrical grounding circuit? I've heard that is a common cause of hesitation in the WRX.

and Whitecel,
You're right, the EJ20 does "run out of steam" past 6K RPM and it is due to the small stock turbo.

 

I've heard it's the ECU switching from open loop to closed loop (or vice versa)???

 

mine was doing just about the same thing and the check engine light came on. the dealership told me my car was running lean from bad gas. it may or may not be that simple, just my two cents.

 

That was only an issue with the 04/05 model from my understanding. Since this cat has an 02, the only things that came to mind were the already mentioned vacuum leak and grounding. And I doubt the dealership will even recognize it as a problem, which sucks for him.