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Old 06-23-2014, 01:40 PM   #1
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Default What sounds like knock, but isn't?

Turbo is in, everything is up and running, getting fuel dialed in and still using base spark map, 93 octane fuel.

I have a sound that sounds just like this: http://youtu.be/6xTWHJADFe8

It happens consistently under load, and stops when I lift.

"Dude, that's knock " right?

Only thing is, it sounds like it's coming from the rear left tire well area.

Still sounds like knock! Sounds can be deceptive on where they're coming from! Especially in a convertible! Right?

Except I'm 99% sure I shouldn't be knocking running 93 octane on a reverant spark base map.

Also, my megasquirt is not pulling timing. Also, the knock sensor gauge in tunerstudio holds steady at 3-5% when the noise is going off. I also got the noise to happen on some bumps, both in neutral not under load, and also with the injectors off cruising in gear off the gas down a hill.

Finally, I've pulled and inspected the plugs and they're good..

So what could it be?
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Old 06-23-2014, 01:44 PM   #2
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Rocks hitting the tire well area from that trubo powerrrrrr
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Old 06-23-2014, 01:47 PM   #3
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you have a 90-94?
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Old 06-23-2014, 01:48 PM   #4
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Lol yeah, but it's CONSTANT while on throttle.. I plan to get the car up in the air *again* (such a PITA because racecar) and if I dont' manage to fix it, I'll get a video later today.
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Old 06-23-2014, 01:48 PM   #5
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you have a 90-94?
99
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Old 06-23-2014, 01:51 PM   #6
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retard the timing in boost by 10* and see if that makes it go away, otherwise it could be the wastegate rattling or any other noise.
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Old 06-23-2014, 01:54 PM   #7
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retard the timing in boost by 10* and see if that makes it go away, otherwise it could be the wastegate rattling or any other noise.
Sorry, to be clear by "under load" i mean even at -10in hg just barely touching the throttle. I can try pulling 10* in even those areas and see if it helps.

I've had the car up 3 times in the last 24 hours trying to find this BS.. Need to drive up onto 2x4s just to get the jack under it because racecar. >:(
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Old 06-23-2014, 01:55 PM   #8
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Maybe hook up a timing light and check base timing too.
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Old 06-23-2014, 02:02 PM   #9
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Maybe get some det cans... I have the 9v powered ones that were sold on here at some point I could lend you if you pay for shipping there and back. Definitely be better at isolating where the sound is coming from.
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Old 06-23-2014, 02:07 PM   #10
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I'll double check base timing again, but it was good when I installed the MS a couple days ago.

If I don't locate it today, I'll be making a trip to the hardware store to pick up another mechanics stethascope as well as a copper pipe and some extra tube to build a set of det "cans" to try to locate it.
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Old 06-23-2014, 02:12 PM   #11
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Quote:
Originally Posted by mlev View Post
Sorry, to be clear by "under load" i mean even at -10in hg just barely touching the throttle. I can try pulling 10* in even those areas and see if it helps.

I've had the car up 3 times in the last 24 hours trying to find this BS.. Need to drive up onto 2x4s just to get the jack under it because racecar. >:(
remove hood and drive. or just pop hood and find the rattle...
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Old 06-23-2014, 07:50 PM   #12
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Found it. Rear left wheel well, just like I thought.

My left half-shaft is rubbing on my new exhaust (the custom built one from 18psi, not the enthuza).

Looks like I just need to get it to sit a quarter inch or so lower. No biggie.


For the record, this is what it sounded like from in the car. (wear headphones. it's hard to hear over the exhaust in this video, but it's loud as **** when you're driving).

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Old 06-24-2014, 12:55 AM   #13
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Put longer hangers on two of the.. hangers.. And it's like a whole new car. Exhaust is quite a lot quieter when it isn't rattling all over the place.

I dropped it low enough that I was worried about it bumping the rear subframe "ladder" brace, so I wrapped it in those areas with header wrap.

I love this car.
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Old 06-24-2014, 02:59 AM   #14
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you welded it back together on the car right?

never rattled on my car. and I mean ever
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Old 06-24-2014, 08:49 AM   #15
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So I am taking it that the front of the turbo has not fallen off again?
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Old 06-24-2014, 09:21 AM   #16
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Quote:
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So I am taking it that the front of the turbo has not fallen off again?
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Old 06-24-2014, 12:40 PM   #17
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Quote:
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you welded it back together on the car right?

never rattled on my car. and I mean ever
Would have liked to at least tack weld it with it fitted, unfortunately it wasn't possible to get either the welding equipment to the car, or to get the car to the welding equipment.

That being said, there was an area of it which we noticed had been hammered in for clearance while we were welding, right where the 2.5 and the 3" come together, and that area was where it was rubbing on my car--I realized it was the same spot when I lowered the exhaust to consider hammering it in for clearance.

It's fine, I put a slightly longer rubber hanger on just behind the axle-back, and on the one hanger on the midpipe, and it hangs low enough now to clear.

It bangs on the subframe brace every now and then on big bumps, but I wrapped the brace in header wrap and it's really good now.

--

And no Lars the front hasn't fallen off yet--but I did make it about 700 miles last time before it came apart... I'll be turning up the boost today, here's to hoping the c-clamp can hold le ubar boost pressure this time..
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