2004 STi Type UK: Losing boost when rev is around 4000rpm

Skipper555

Sunday Drivers
Hi everyone,

As of this afternoon my STi is acting a bit funny when I push it and it's revving around 4000rpm (feels like fuel cut) but I believe it's related to the turbo, not feeling the boost. This won't happen if I rev it steady and gently, only when I floor it.

I was told this could be the issue "I think one of the little pipes has popped of the boost control . Take a look around the boost actuator or boost control solenoid"

Any feedback or directions (including images) appreciated. I'm not a professional mechanic.

Thanks,

Rafa
 
dont think thats a boost issue. First thing is pull the plugs and check them, then gap them if not already done to 0.6
Try that first let me know how u get on
 
Sounds like it could be "boost cut" alright (ECU feature to protect your engine).

Few things could cause it and best to get it plugged in (OBD) so you can read the diagnostic data to help identify the issue.

See if there are any DTC/CEL s recorded, see what boost it is running while driving and how the boost behaves on easy acceleration vs fast etc (log actual boost pressure vs requested/demand pressure and see how the values track, or don't track each other). That will be able to give a good indication of where to start looking (boost control solenoid, actuator, vacuum pipes, etc). Also check the Knock sensor values while logging and the lambda/AFR (if bad ignition due to failing coilpack or plug the value will suddenly read as very rich as ignition fails (in 1 or more cylinders) and unburned fuel goes out the exhaust).

Nothing wrong with checking plugs. If newish just check gaps and also appearance of plugs in case one is fouled or wet could also be a coil pack starting to act up - or if in the car for over 15k miles then best to replace them. If Iridium plugs they should not be "gapped" as can damage plug (electrode) and can lead to big engine damage if bits break off the plug if inside the engine.

Note that although "boost cut" is an ECU safety feature, it doesn't mean it will definitely protect your engine. So drive it easy till you find and fix the problem to minimise the chance of critical / expensive engine damage.

Good luck!
 
dont think thats a boost issue. First thing is pull the plugs and check them, then gap them if not already done to 0.6
Try that first let me know how u get on

First of all thank you both for your suggestions.

So after taking the car to 2 mechanics who couldn't give me any precise feedback, I ordered new spark plugs (Denso) and replaced them with my brother's help and it worked! I feel the power again as it should.



I'm quite disappointed with the level of service provided around. When I took my STi to Portugal last summer, the mechanic there was glad to have an STi and even washed it for me...here people could care less.
 
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First of all thank you both for your suggestions.

So after taking the car to 2 mechanics who couldn't give me any precise feedback, I ordered new spark plugs (Denso) and replaced them with my brother's help and it worked! I feel the power again as it should.



I'm quite disappointed with the level of service provided around. When I took my STi to Portugal last summer, the mechanic there was glad to have an STi and even washed it for me...here people could care less.

Judging by the photo those plugs are in it years , gap looks 2mm or possibly more .
Most places don’t have the knowledge or experience with these cars and wouldn’t have the first notion how to approach working on them.
 
First of all thank you both for your suggestions.

So after taking the car to 2 mechanics who couldn't give me any precise feedback, I ordered new spark plugs (Denso) and replaced them with my brother's help and it worked! I feel the power again as it should.



I'm quite disappointed with the level of service provided around. When I took my STi to Portugal last summer, the mechanic there was glad to have an STi and even washed it for me...here people could care less.

You are welcome. Great feeling when you sort a problem like that. Feel free to ask away if you ever need advice.
 
Unfortunately, the problem is not gone completely. Yesterday I went for a motorway drive and oddly enough it's happening when I floor it on higher gears 3 and 4 (once again it feels like it's misfiring and minor loss of power can be noticed). Later on I tried it and it did not happen when I floored it on 1st and 2nd.

Will check if spark plugs are tight enough and go for another spin today. I'm so frustrated right now...:banghead:
 
Will boost higher up in the higher gears due to engine load.
Sounds like fuel/boost cut
I wouldn’t push it until you get someone to look at it as you could damage the engine , put a boost gauge on see what’s happening there
 
Had a chat with another person today and he believes the spark plugs I purchased are incorrect for my STi model. The ones I bought are only a 6 heat range (the correct ones needs to be a 7 heat range with smaller gap).

I was told to purchase these: https://www.sparkplugs.co.uk/ngk-spark-plug-bcpr7es

Does the suggestion above sound right?

uSu.jpg
 
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Heat range 6 or 7 won't cause what's happening . Did you check the gap on them to .6 -.65
 
i recon the new plugs you have now with the 8mm gap are to wide a gap for the spark.

if you regap them to 6-7mm it should be fine, just be careful not to damage the tip.
 
yep as the guys said, heat ranch not the cause. Its sounding very much like plug gap. Pull the plugs out and gap them correct to between 0.6-0.7
Also not sure if I read your post right about tightening the plugs more. Dont do that if you did say that. Just tighten normal. dont put all your strength into it otherwise you will damage the thread. They dont need to be tight, they must be tight enough so the seal nicely on the head. Like putting a cap on a bottle.
 
It wouldnt be the spark plug or the gap imo for issues your having.



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Thanks again everyone. My initial post mentioned boost, but after proper testing I noticed it's not necessarily accurate. It's a misfiring feeling and hesitation (the power curve is not completely smooth when I floor it). I can hear the turbo working ok when it's not under full acceleration.

Either way, I'll be taking it back to Joe (TDR Performance), as this all started happening after the remap (302hp now). Prior to the remap, car was running absolutely perfect and I had the following done to prepare: new walbro fuel pump, new clutch kit and now brand new plugs, which did not fix this odd issue. Joe is supposed to run a diagnosis and pinpoint the problem. I'm hoping the actual problem can be found.

If you know any garage in North or West Dublin, which knows how to work on Subarus, please let me know (I may need one after I take it to Joe).

Thanks.
 
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May possibly be a ****y neutral position switch. That can cause havoc with avcs as car thinks in neutral whilst seeing speed and throttle etc etc

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It sounds fuel related to me, maybe a bad fuel reg, but it could be bad or weak coil packs, we are all only really guessing from our Sofa’s lol..
it’s very easy to crack the ceramic on spark plugs when fitting them especially if using swivel joints, so if not familiar with these, be careful.
 
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Not as common as bug eye for that.

Quick fuel reg pressure check under load

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You know yourself, all we can do is throw possibilities at it. By the sounds of it the op needs someone to do a bit of proper diagnosis on it... wonder is it a duff ebay Walbro pump...hmmmmm lol.. possibilities are endless
 
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