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M35 Help - Shudder @ 2500rpm

Blek

By Blek,
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Blek

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Evening all,

Was driving home on the F3 (M1, whatever!) tonight and the just noticed the car 'shuddering' at around 2500rpm. Not a heaps violent shudder or anything like that, but definitely noticeable. I managed to creep my way up to 110kmph, no worries, but anytime I gave it a bit more gas and it would drop to fourth revs go up etc I would get the shudder again. I nursed it back onto Pennant Hills Road, and did a bit of testing and confirmed, definitely shudders at around 2500rpm, irrespective of higher speeds etc.

I know this is about when the turbo starts boosting, but driving the car under 2500rpm seems fine. Can hear the turbo whining per usual. No errors on the dashboard or anything, idles fine, engine doesn't stall. Thinking possible leak somewhere/vacuum lines.

Wondering if anyone else has experienced something similar to this before? Trying to narrow it down.. bit dark out there to go check lol

Car is a 2001 AR-X, stock except zorst., 123,xxx kms.

Cheers

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C34stagRB Newbie

C34stagRB

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I have a c34 stagea..i have a similar problem when at high revs..it has a shutter loses bit of power..and has a small like shutter when it idles...i think mine is fuel pump..because if i keep tank full or above half doesnt do it once...if i gets down near like quarter tank..it starts happening again...

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Daleo Grand Master

Daleo

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Evening all,

Was driving home on the F3 (M1, whatever!) tonight and the just noticed the car 'shuddering' at around 2500rpm. Not a heaps violent shudder or anything like that, but definitely noticeable. I managed to creep my way up to 110kmph, no worries, but anytime I gave it a bit more gas and it would drop to fourth revs go up etc I would get the shudder again. I nursed it back onto Pennant Hills Road, and did a bit of testing and confirmed, definitely shudders at around 2500rpm, irrespective of higher speeds etc.

I know this is about when the turbo starts boosting, but driving the car under 2500rpm seems fine. Can hear the turbo whining per usual. No errors on the dashboard or anything, idles fine, engine doesn't stall. Thinking possible leak somewhere/vacuum lines.

Wondering if anyone else has experienced something similar to this before? Trying to narrow it down.. bit dark out there to go check lol

Car is a 2001 AR-X, stock except zorst., 123,xxx kms.

Cheers

Hi mate, it sounds like your AFM has failed.

Do you have a light on the dash?

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Blek Collaborator

Blek

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G'day Dale.

Thanks for your response. I've read about the troubles with afm's, but symptoms sounded a bit different to mine? ie no errors in the dash and car isn't stalling..? Still, afm is a good thing to have spares of, where are ppl getting theirs these days? Wrx sti compatible or is the verdict out on the cheap Chinese versions?

Btw, I took the car for a short drive yesterday. Seems the shudder/hesitation kicks in around 3000rpm now.. So much more drivable lol :P

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Daleo Grand Master

Daleo

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They don't always fail with the characteristic mil light and no idle, I've had one that would only fail when the intake temp went over 37 degrees, and it would only make the car stall at idle. Everything else was fine.

The current issue doesn't seem like the typical AFM symptoms; but checking all coil plugs and AFM plug is seated properly would be a good start, and making sure all the small vac hoses are connected in the plenum and valley area.

Maybe check all cooler piping for loose clamps and possible split joiners.

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Blek Collaborator

Blek

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They don't always fail with the characteristic mil light and no idle, I've had one that would only fail when the intake temp went over 37 degrees, and it would only make the car stall at idle. Everything else was fine.

The current issue doesn't seem like the typical AFM symptoms; but checking all coil plugs and AFM plug is seated properly would be a good start, and making sure all the small vac hoses are connected in the plenum and valley area.

Maybe check all cooler piping for loose clamps and possible split joiners.

Cheers Dale. Hopefully I will get some time to check it out over the weekend.

Is it blowing smoke at all? Mine had similar symptoms to what you're describing plus the smoke blowing.

mmmmm Not really.. just a normal amount of white vapour-like smoke which disperses quickly, not something I would worry about. What was the issue with yours in the end, Duncan?

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Dunc Mentor

Dunc

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mmmmm Not really.. just a normal amount of white vapour-like smoke which disperses quickly, not something I would worry about. What was the issue with yours in the end, Duncan?

Split in the silicone hose on the cold side of the FMIC, took ages to find.I think I replaced every other silicone hose before I got to that one, as well as coil packs, spark plugs, hose clamps etc. Heres what it was running like:

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West Grand Master

West

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Split in the silicone hose on the cold side of the FMIC, took ages to find.I think I replaced every other silicone hose before I got to that one, as well as coil packs, spark plugs, hose clamps etc. Heres what it was running like:

So is it fixed or it's still missing? Sounds awesome, like anti-lag :)

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Ben C34 Grand Master

Ben C34

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Split in the silicone hose on the cold side of the FMIC, took ages to find.I think I replaced every other silicone hose before I got to that one, as well as coil packs, spark plugs, hose clamps etc. Heres what it was running like:

https://www.youtube.com/watch?v=0QotAsFh7mc

A pressure test would have found the leak instantly.

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Dunc Mentor

Dunc

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A pressure test would have found the leak instantly.

Yes, if I'd had a kit or anyone I know had a kit I'd have used it.

So is it fixed or it's still missing? Sounds awesome, like anti-lag :)

Fixed ages ago, it was a pig to drive getting on to boost as it basically leaking air and over fuelling (as you can tell) at about 3-3.5k

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