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Discussion Starter · #1 ·
Hey all, I'm wondering if I can get some opinions on a weird problem I've been chasing down.

I've got a 2011 wrx (90k on the clock) with a cobb dp, sf intake and (currently) cobb stg 2 sf 93 map (among other, unrelated things) that's got a weird RPM surge issue at peak boost/torque.

In 3rd and 4th at WOT, I'm feeling a loss in power (doesn't put me back in my seat like it used to) and the RPMs jump up about a 1k. The engine isn't cutting out as far as I can tell, or dropping RPMs, boost appears to hold steady, it just feels like it's not putting power down any more. It runs very very rich during, as well (like 10 flat).

I've cleaned my air filter, MAF sensor, replaced the TB-IC hose (it collapsed a while back) with a mishimoto hose. I've looked for loose/disconnected/split hoses and haven't seen anything, my IC end-tanks look good too. The only thing I haven't checked thoroughly is the turbo inlet hose (given how inaccessible it is) but I did notice yesterday that the clamp on the hose at the turbo side was hand loose. I've tightened it up but the issue persists. More to the point, is it possible that a split/torn inlet hose could cause these kinds of issues?

Could it be the clutch? I tried to get it to slip in 5th at around 30-35mph but it holds. Bad gas? Fuel filter? Spark plugs? Should I do a compression test?

Sorry if I'm forgetting anything, and I have searched for a while on this. Thanks for any guidance you can provide!
 

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In 3rd and 4th at WOT, I'm feeling a loss in power (doesn't put me back in my seat like it used to) and the RPMs jump up about a 1k. The engine isn't cutting out as far as I can tell, or dropping RPMs, boost appears to hold steady, it just feels like it's not putting power down any more.
This sounds like classic clutch slip. If you are at 90k miles without ever having replaced the clutch this is the most likely culprit.

It runs very very rich during, as well (like 10 flat).
What tool are you using to measure A/F?


I tried to get it to slip in 5th at around 30-35mph but it holds.
What in the hell are you doing trying to get the clutch to slip IN 5TH GEAR GOING 30-35 MPH!? This is terrible for the car. Clutch slip is most likely to happen at high RPMS in a high gear while in boost. If you are trying to get the clutch to slip in 5th gear you need to be going at least 70-80mph....

To me this sounds like a couple of problems. The random and fast 1k rise in RPMS while the car isn't physically going any quicker is textbook clutch slipping. But if you are reading A/F on a wideband o2 sensor and are seeing a 10 A/F when wide open throttle then there is also another issue. If you are measuring A/F ratio with a Cobb AP, then this measurement is invalid as it uses the stock narrow band o2 sensor which doesn't give an accurate reading when outside of stoich.
 

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Discussion Starter · #3 ·
This sounds like classic clutch slip. If you are at 90k miles without ever having replaced the clutch this is the most likely culprit.



What tool are you using to measure A/F?




What in the hell are you doing trying to get the clutch to slip IN 5TH GEAR GOING 30-35 MPH!? This is terrible for the car. Clutch slip is most likely to happen at high RPMS in a high gear while in boost. If you are trying to get the clutch to slip in 5th gear you need to be going at least 70-80mph....

To me this sounds like a couple of problems. The random and fast 1k rise in RPMS while the car isn't physically going any quicker is textbook clutch slipping. But if you are reading A/F on a wideband o2 sensor and are seeing a 10 A/F when wide open throttle then there is also another issue. If you are measuring A/F ratio with a Cobb AP, then this measurement is invalid as it uses the stock narrow band o2 sensor which doesn't give an accurate reading when outside of stoich.
Hey thanks for responding; I'm using an AEM wideband AFR gauge.

The thing that's weird about it is that I can feel what I can only describe as some acceleration. It's not like I'm pegging the throttle in neutral. If that makes sense.
 

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Hey thanks for responding; I'm using an AEM wideband AFR gauge.

The thing that's weird about it is that I can feel what I can only describe as some acceleration. It's not like I'm pegging the throttle in neutral. If that makes sense.
It usually starts less subtle then as time goes on it gets worse exponentially. At what point in the RPMS do you notice the sudden jump? Also, have you pinpointed a time in which the AFR reads 10? If so, at what RPMS and scenarios?
 

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Discussion Starter · #5 ·
Yeah, you're probably right. I'm sure part of me doesn't want it to be the clutch given the cost.

What I've noticed is: 3rd gear past 3.5k (@WOT) it goes rich, then jumps up 500-1000 RPMs and holds for a second, then seems to grab again (though still no torque/power)

4th gear: same scenario but it never grabs back, RPMs just climb and climb until I let off (usually quickly for fear of breaking something).

For the sake of clarity I try to avoid doing this as I feel like I'm gonna test it one too many times and blow something up.

thanks again for responding. I posted on nasioc but got one or two responses.
 

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Yeah, you're probably right. I'm sure part of me doesn't want it to be the clutch given the cost.

What I've noticed is: 3rd gear past 3.5k (@WOT) it goes rich, then jumps up 500-1000 RPMs and holds for a second, then seems to grab again (though still no torque/power)

4th gear: same scenario but it never grabs back, RPMs just climb and climb until I let off (usually quickly for fear of breaking something).

For the sake of clarity I try to avoid doing this as I feel like I'm gonna test it one too many times and blow something up.

thanks again for responding. I posted on nasioc but got one or two responses.
Yeah, no doubt you need a new clutch. I can't comment with certainty on running rich though. That could be a few things, all of which you have already looked for. You are running an OTS map, which is not necessarily perfect. This could be the cause of that issue.

First you will need to get your clutch replaced. Next, if the running rich issue isn't mechanical, you'll need to consider a professional tune as that will be the best way to truly dial in AFR.
 

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*BUMP*
I am curious if replacing the clutch fixed the issue. I have a very similar setup AND issue. However, I experience a RPM dip after it surges.. anywhere from 200-800 RPMs. If I can resurrect this thread, I will share some logs or whatever it takes to figure this thing out! I will take a look at what my AP gives me for air/fuel measurements. Just did a pressurized smoke test - intake side - and it appears to be leak free.
 

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Have you checked for exhaust leaks? Logs would be helpful
 
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