strange exhaust noise...

[sktz-34]

Hey guys,

I'm not sure if anyone can help me, or knows what's wrong... so here goes...

My R34 GTT has a HKS hi-power exhaust, custom dump, with a catco cat and a resonator. When i'm giving it a bit of stick, it makes a funny noise. It sounds like I'm hitting rev limiter (i know i'm not though, cos the rev's are still rising when i hear it, and it's around 5000rpm). I've recently put a cat on because i thought it was something to do with back pressure, or something. But it still happens even after i have put on the cat.

The noise is hard to describe, it sounds like it's restricted, and can't get more airflow... and i can notice the power drop when it happens.

It's soo farken gay, when ppl hear it they think i've hit rev limiter cos that what it sounds like... and i'm like.. WTF is that noise!

I hope someone can help me! Thanks in advance guys.

Regards,

Shaun

[sewid]

Hmm... when this happened on my old R33 gtst it was the ECU limiting/cutting boost. I dont know if R34 GT-T do the same thing. Might need an ECU upgrade.

[NJR 34GTT]

Could possibly be boost/fuel cut. If it starts jerking and revs drop that would be my suggestion. Mine very occasionally does it on very cold mornings if i hit 15psi.

Another possible suggestion is that the turbo is sucking the afm to turbo duct closed. Only really a possibility if you are running higher than stock boost.

[JAPCAB]

Is it a popping noise? how quickly does it happen (pops per second?)

[sktz-34]

see the thing is, the only mods my car has is the exhaust and a HKS are filter - i havn't touched the boost!

i wouldn't have thought running it stock would have a problem with the ECU, so wtf!

JAPCAB - pop as in like the pop on de-acceleration? if so, then it's not that. my car does pop when gearing down, and when it's real cold, but this is different! as i said, it's hard to explain. Imagine you booting it in second gear and at about 4.5-5 k rpm, no more increase in power and it sounds like ur rev limiting, and u can hear the noise from under the car - WTF! that's y i thought it was cos i wasn't running a CAT, but now i have one it still does it! i'm lost...

[JAPCAB]

Hrmm so you'll hit 4.5-5K and its like the rev limiter is set at that rpm and you cant boot it anymore? does it happen intermittently? or occasionally? Perhaps an ECU reset might do the trick if you are running standard ECU? unplug battery to do this.

see the thing is, the only mods my car has is the exhaust and a HKS are filter - i havn't touched the boost!

i wouldn't have thought running it stock would have a problem with the ECU, so wtf!

JAPCAB - pop as in like the pop on de-acceleration? if so, then it's not that. my car does pop when gearing down, and when it's real cold, but this is different! as i said, it's hard to explain. Imagine you booting it in second gear and at about 4.5-5 k rpm, no more increase in power and it sounds like ur rev limiting, and u can hear the noise from under the car - WTF! that's y i thought it was cos i wasn't running a CAT, but now i have one it still does it! i'm lost...

[sktz-34]

Hrmm so you'll hit 4.5-5K and its like the rev limiter is set at that rpm and you cant boot it anymore? does it happen intermittently? or occasionally? Perhaps an ECU reset might do the trick if you are running standard ECU? unplug battery to do this.

it does happen intermittently, that's why i'm so confused. If it were happening every time, then i would have to blame the ECU. But it happens every now & again, but it's more often now than before (probably cos i'm booting it more, and trying to figure out what it is!). And yes, it's a stock ECU, unless the person who had it before me had played around with it - but i doubt it cos it was 100% stock when i got it.

Regards,

Shaun

[Ant97GTR]

Hey Shaun,

Check your spark plugs and coils....had exactly the same prob in my R33.....changed the coils over as the plastic casings were worn and cracked......problem hasn't come back

[sktz-34]

Hey Shaun,

Check your spark plugs and coils....had exactly the same prob in my R33.....changed the coils over as the plastic casings were worn and cracked......problem hasn't come back

hey man, thanks for that. i will be sure to check it out this weekend (now that i've got something to check out! didn't know where to look before...)

thanks

Regards,

Shaun

[Ant97GTR]

No probs man thats what these forums are for

My problem went something like this......with 1/2 the accel pedal down the problem never appeared and was only when giving it full pedal that it would happen. As you described it kinda like hitting the rev limiter at around 5000-5500rpm for an instant - the car would kinda pause for a second and then rev all the way to the redline. The way it was explained to me is that under 1/2 load the current through the coil pack is less and the whole spark is delivered to the spark plug. Under full load the max amount of current is passing through the coil pack and if there is even a hairline crack in the plastic casing the spark will 'escape' and ground on your engine block....thus the spark plug isn't fed and on that particular revolution of the engine you are missing one cyl hence the miss sound and pause in acceleration.

Anyway this was my problem and a new set of coils fixed it instantly.

Good luck with the fix....

[predator]

what ant said definitely seems likely..

could also be an exhaust manifold leak, dead gasket or something like this.. really there are a large number of things you'll have to check one by one.

[sktz-34]

No probs man thats what these forums are for

My problem went something like this......with 1/2 the accel pedal down the problem never appeared and was only when giving it full pedal that it would happen.  As you described it kinda like hitting the rev limiter at around 5000-5500rpm for an instant - the car would kinda pause for a second and then rev all the way to the redline.  The way it was explained to me is that under 1/2 load the current through the coil pack is less and the whole spark is delivered to the spark plug.  Under full load the max amount of current is passing through the coil pack and if there is even a hairline crack in the plastic casing the spark will 'escape' and ground on your engine block....thus the spark plug isn't fed and on that particular revolution of the engine you are missing one cyl hence the miss sound and pause in acceleration.

Anyway this was my problem and a new set of coils fixed it instantly.

Good luck with the fix....

well there you go, sounds exactly like what's happenening to me!

just a quick question, how much would it be to fix the coils? Thanks again man.

Regards,

Shaun

[Abo Bob]

Heaps. $600-700 for a new set I think. Mine went at about 67000kms.