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Cutting out at high rpm, wot. Stuttering from 4500+ rpm,

Customer Question
Cutting out at high...

Cutting out at high rpm, wot. Stuttering from 4500+ rpm

Mechanic's Assistant: What is the model/year of your Subaru?

2004 wrx with jdm v7 sti motor/ecu

Mechanic's Assistant: How many miles are on the car? Is it an automatic or a manual transmission?

Manual

Mechanic's Assistant: Are you fixing your WRX yourself? What have you tried so far?

Swapped maf. swapped bcs. changed plugs. cleaned all electrical connections

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Cleaned air filter. getting 12.9 vdc from battery while off, 14+ while running. alternator belt looks good

Submitted: 7 months ago.Category: Subaru
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Answered in 14 minutes by:
12/3/2017
Subaru Mechanic: Gabriel Grey, Auto Service Technician replied 7 months ago
Gabriel Grey
Gabriel Grey, Auto Service Technician
Category: Subaru
Satisfied Customers: 448
Experience: Master Service Technician
Verified

G​ood evening, I hope you are doing great. My name is***** would be happy to assist you with this.

​Does the car currently have any trouble codes stores? Have you noticed what the boost pressure is at when it starts to stutter?

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Customer reply replied 7 months ago
On 50 mile trip car ran fine. On return trip it was about 30 degrees cooler. On wide open throttle, car would shudder and stutter at 4500 rpm to redline. Fuel cut. Pulled off to a gas station as i thought it was bad gas (car had sat for 3 weeks). Filled up with 93 octane (about 98 ron which is what this ecu runs stock) Car wouldnt start.
Popped hood and saw loose battery terminal connection. It was broken.
Replaced:
battery terminal, and problems persists.
replaced maf
cleaned map
replaced fuel filter
checked grounds
ran injector cleaner
Customer reply replied 7 months ago
It did have p0340 cam position sensor as i was at full boost (18 lbs) and went over a bump. I have taken the cam position sensor off and it had some oil in the j connector, as its right under the oil filler neck and i probably spilled some. There no stored codes and this has not returned after clearing. The sensor is at 2kohms, which is in range.
Customer reply replied 7 months ago
Stutter is rarely 2nd gear.
3rd through 5th gear the stumble is almost always evident at full boost but is like hitting a wall at 4500 rpm at times.
Customer reply replied 7 months ago
car has been the same for several years with never a problem.
Customer reply replied 7 months ago
I thought the bcs wastegate was bad so swapped it out. Then checked wastegate after removing downpipe and it seems to function smoothly.
Customer reply replied 7 months ago
replaced wastegate control solenoid, not the wastegate
Subaru Mechanic: Gabriel Grey, Auto Service Technician replied 7 months ago

H​mm that is strange, I would have suspected a fuel issue as well. Have you manually tested the fuel pressure? It might be worth checking the readings when it hits 4,500 to make sure the pump is keeping up

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Customer reply replied 7 months ago
I have not logged fuel pressure but can do that tomorrow. what other paramters should i log? throttle, manifold pressure, fuel pressure, timing advance, and speed?
Subaru Mechanic: Gabriel Grey, Auto Service Technician replied 7 months ago
Yeah check fuel pressure and fuel trims. Also make sure the throttle/pedal positions are correlated with each other
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Customer reply replied 7 months ago
https://docs.google.com/spreadsheets/d/132C8RBQh-3hdWYPr02Onjr6esBNk20WYEQvZR6Kb6yo/edit?usp=sharingCannot find exact fuel pressure, only fuel pump duty. It looks like timing is jump all over on wot. a/f learning is under 5%, wth very lttle fine learning knock correection.
Subaru Mechanic: Dan, ASE Certified Technician replied 7 months ago
Dan
Dan, ASE Certified Technician
Category: Subaru
Satisfied Customers: 2,113
Experience: Dealer Auto Technician
Verified

Different expert here, do you still need help?

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Customer reply replied 7 months ago
sir. swapping coilpacks tomorrow.
Subaru Mechanic: Dan, ASE Certified Technician replied 7 months ago

Is the engine misfiring?

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Customer reply replied 7 months ago
no codes for misfire. only shudder/hesitation at wot high boost
Subaru Mechanic: Dan, ASE Certified Technician replied 7 months ago

These engines are common for broken ring lands. Have you done a compression or leak down test?

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Customer reply replied 7 months ago
About 6000 miles ago at 75,000 miles it was 145 all around
Subaru Mechanic: Dan, ASE Certified Technician replied 7 months ago

Do you have any boost leaks? Have you checked the fins on the turbo?

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Customer reply replied 7 months ago
No boost leaks, turbo looks fine
Subaru Mechanic: Dan, ASE Certified Technician replied 7 months ago
Disconnect the coil pack connectors one at a time with the engine idling. Listen for the rpms to change. If no change you have a dead cylinder. Does the engine idle rough?
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