Weird knock issue ? :(

[ST240]

So after putting my rb30 back together (entire engine was apart, replaced rod bearings), ive driven it around 200 km or so on a rough tune.

Recently ive noticed a knocking sound. It only occurs around mid to high load, and only at above 3k rpm. If i bring the RPM up very slowly i can get to 6k+ RPM, i cant hear it. It also doesnt occur revving the crap out of it it neutral. When I hear the sound, boost is just building up to 0 and thats it.

Does that seem like rod knock? or spark knock due to a bad tune? Or what the heck... It didnt seem so apparent when i first started driving it around. How much timing would i have to kill to get rid of the sound if it was knock? I richened the hell out of it in that region like 10.5:1 .

Im thinking lifters maybe? (r32 rb25de head)

Im so confused....

[TM_S13]

at first thaught it seems like some of the turbo exhaust gaskets are gone, or the exhaust manifold gaskets to the head... they can give a rattle sound and since there's a leak the turbo won't build boost...
though, you say that when reving slowly it doesn't happen... so that might not be the gaskets
what do you have to control boost ?

try and get someone else to drive the car while you're sitting with the laptop doing a log and tracing at the same time so you can mark the point where it starts and compare with AFR's, timing, load, etc...

best way to detect knock is to use some det-cans. if you use them too you'll clearly see, or better, hear what can it be...

[ST240]

I use a bosch knock sensor amplified thru my laptop for detecting knock

Heres some videos of the sound

http://www.youtube.com/watch?v=L0aDi_KCDQo

It should be pretty obvious, but you can hear it best at 0:09-0:11 and again at 0:38.

Edit:

The sound in this one is even better:

http://www.youtube.com/watch?v=jOvG7s8CZJ0

[TM_S13]

it does sound weird... can't exactly tell if it's det noise or engine mechanical knock noise

[raddy]

what about some strange type of compressor surge? are you using standard turbo for that engine?

[ST240]

God no. It's a Holset HX35... similar size to a GT35 ish. It would have to go thru that range to build boost tho so how could it be surge?

[ST240]

Ok this is really starting to piss me off... Its spark knock, no its rod knock, no its the lifters, no its spark knock. No.

It definately isnt spark knock. Just logged a run, AFRs in the low 10s, timing was 10* (!) map was anywhere from vac to 4 psi. And it still makes the sound as loud and as consistent as ever. Please tell me that isnt spark knock, although i wish it was.

Any ideas anyone?

I've attached the log. Aux1 is hooked up to a well calibrated map sensor.

[Eric]

it's a bit hard to hear in the video, but that doesn't sound as spark knock/detonation to me...more like something mechanical.

Could it be the engine/exhaust is hitting something because of the engine tilting/rolling in it's mounts ?

[Bernardd]

I had what sounded like severe knock which ended up being the flexplate bolts that were backing out.

[PL]

I had an S15 SR20DET on the dyno once that sounded like it was knocking. I had the tune in such a safe place that I knew it wasn't. But I actually had people running into the dyno cell telling me they could hear knock from the other room. It was the VCT mechanism...

PL

[ST240]

I had an S15 SR20DET on the dyno once that sounded like it was knocking. I had the tune in such a safe place that I knew it wasn't. But I actually had people running into the dyno cell telling me they could hear knock from the other room. It was the VCT mechanism...

PL

Someone else suggested that. I wish that was the problem.

Just changed my oil and found small shiny particles. I think a bearing is spun. And winter is here in one month and i didnt even get to tuning FML.

[PL]

Hmmmm. That normally shows up as seeming OK at idle, then you give it a rev and you get a little rattle at certain RPM just as you lift off. I guess if it's bad enough it'd do it all the time. Either way it's a pretty distinctive sound. I hope it's not that. Bit's in the oil doesn't sound hopeful though...

PL

[ST240]

Hmmmm. That normally shows up as seeming OK at idle, then you give it a rev and you get a little rattle at certain RPM just as you lift off. I guess if it's bad enough it'd do it all the time. Either way it's a pretty distinctive sound. I hope it's not that. Bit's in the oil doesn't sound hopeful though...

PL

Yeah. I cant get anything consistent as far as peoples opinions go. But people have had rod knock in a load only condition like me before so...Better safe than sorry maybe. Id like to try disconnecting one injector and one coilpack at a time, trying to drive it and seeing if i could isolate it. But I really don't want to wreck the crank.