Bigsyke

When going WOT, once in a blue moon it would sound as if one bank was high-pitched, and the other bank was low-pitched. I initially thought I was dropping a cylinder, but the sound evened out when I would let off the gas or change gears. Weeks would go by without this strange, alien sounding exhaust happening--only in a single gear (For the entire rpm range, but clearing up fully on the next gear).

Revup, Megan V2's and Y-pipe, Uprev tuned.

When I recently installed my motive performance cat-delete, this sound is maybe 40% of each WOT pull. Datalogging doesn't show anything, but it's clearly mechanical/non-exhaust related. Would a dropping cylinder show a cel? Bank 1 is richer than bank 2 by about 0.5 afr's, but I don't see any afr inconsistencies when the acapella exhaust sound occurs. Literally sounds like two different cars packed into one. No exhaust leaks, and no vacuum leaks, no cel.

I'm narrowing this down to possible oil consumption in a single cyilnder, or CKP or maybe a CPS. Does this sound logical?

SmoothZ

iTrader: (13)

That's quite the explanation and very detailed. Not sure if that theory of the cylinder would throw a code, but what do I know? I'd have to hear it to understand what you're explaining. All I know is based on my personal experience, going WOT makes a consistent even sound.

guitman32

iTrader: (15)

May or may not throw a code if its a misfire. Usually can run some time before a code is thrown on a failing pack, for example.

Does it sound like the timing is off? Or is it a smooth sound just two different pitches? Is there any loss of power? Does it always happen in the same gear?

Exhaust vibrations between tight clearances can also cause vibrations that for the life of you may sound mechanical.

When did you first notice the issue?

Bigsyke

Smooth sound, two different pitches.

I thought it was exhaust related, but it became worse after switching ypipe/test pipes.

I first noticed it while doing etunes. It can't be mechanical timing, but I wouldn't doubt an electrical exhaust cam timing issue.

Not sure if it makes any difference, but uprev had to DUMP fuel to get me out of the 17afr range... Odd for just testpipes, ypipe and stune.

Yes, very small power loss, but it's not noticeable due to being a loss that only lasts that rev range. Once I shift, the power generally returns.

It almost seems that, apon going wot into open loop, one bank remains in closed loop... Resmashing the gas pedal makes the offending bank finally go into open loop, evening out the sound. Strange that cipher shows nothing wrong, from what I can see..

PP08HR

iTrader: (2)

Its vtec kicking in bro

Bigsyke

Did some more datalogging. Noticed the Exhaust Cam timings are off between the banks. At one point, during a saxophone duet pull, the discrepancy was around 20 (133 B1 vs 154 B2).

Generally while cruising they are pretty even, with Bank 1 being occasionally 1pt higher than bank 2.

Are they supposed to be dead even at all times? Most hard pulls they were off, with bank 1 being lower.

waldo36

iTrader: (2)

I think I have a similar problem on hard WOT accel. once I hit 3k RPMs and up, my true-dual sounds like a single that's been straight piped. I haven't data-logged any information as I don't have the tools to do so. The sound used to be so deep, but now I feel like people think I'm a high school kid that spent my allowance on the cheapest ebay parts available.

Could it be my HFCs are breaking down and flowing more air making kind of a partial test pipe? Under normal accel below 3k is fine, and mild accel up to 3.5k is ok but then begins to sound terrible. I've had Z1 HFCs installed since around 65k miles, and I'm right about 121,400 right now. Do my cats need changing? And exhaust setup is Crawford headers, Z1 HFCs, and Gemini true dual.

Plus, no CEL and no real performance loss noticed. Only thing that's been different the past few weeks since this has started is the engine seems a little harder to start cold and warm.

calibredz33

it's just noise then? runing a true dual, the exhaust pulses can't even out the flow. the fact that you're on the driver side, may cause one side of the exhaust to sound louder than the other. if the motor is healthy, that cats should be cleaning them self out with the heat generated.
Did it make the note running test pipes? Is one exhaust tip dirtier than the other?
"find out next time one MY350.com!!!"

'WhiteRoadster

Hopefully not a clogging cat, i had this happen before, shortly afterwards i was unable to go past 3k in an ls1 i had

Bigsyke

I'm running test pipes and a nismo exhaust.

Definitely not just noise. Sounds like vtec crossover into a violin vs chello. It's almost every time I hit the has hard now, and its seriously a terrible noise. Trying to beat on it to throw some sort of cel...nothing.

FYI I have an oil burner. 1qt ever 300miles. No real visible smoke during these tests, which is odd. All plugs are equally ashy.

I almost think it's an injector dropping out at higher load. The tuner did have to correct a bank by a significant amount. He suspected a preo2 exhaust leak. I can't find any manifold leaks...would an injector issue throw a cel?

guitman32

iTrader: (15)

Was going to say injector issue based on what you said re: dumping fuel and 17afr, but I think the root cause is timing/cam phasing related.

Your descriptions immediately made me think of sounds like how modern v6s sound when cold and youre just pulling away first thing in the morning.

What year is the Z?

Why dont you get your tuner to load the stock tune and see what happens?

Bigsyke

2005 track.

Pulled over while driving to post this. I've either fixed this, or narrowed it down. Nissan didn't grind down any metal on the ground points, so it was relying on the bolt threads to make a ground. Even though the resistance was fine, I couldn't see anyway there could have been good contact. Ripped out the interior and went to town. Got the two, including the battery grounds in the engine bay as well.

When I went for a test drive, the throttle response was improved 100 fold. The exhaust sounded completely different.

Switching to my tune map, the rasp started, and power was down, however it sounded even. Fingers crossed.

Edit:back to the same old once the car is warned up enough....