Detonations when changing gears

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Apr 28, 2003 | 11:07 AM

rutz964C4

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Racer

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From: Madrid, Spain

Detonations when changing gears

Is it normal to hear sometimes detonations when changing gears?

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

ALEX

Apr 28, 2003 | 11:38 AM

Ade - C4 91

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From: New Zealand

Hi,

I get them very occasionally, and only when the exhaust is really hot. I have a cup pipe fitted.

Ade.

Apr 28, 2003 | 12:21 PM

rutz964C4

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Racer

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From: Madrid, Spain

I also have the cup pipe and a chip installed, but if I remember well it did it also before the modifications.

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

ALEX

Apr 28, 2003 | 04:06 PM

Adrian

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From: Parafield Gardens

Dear Alex,
The answer is NO! Detonations suggest incorrect detonation. This is eventually a timing issue but can be caused by other things like aftermarket chips and cup bypass pipes,
Ciao,
Adrian
911C4

Apr 28, 2003 | 06:10 PM

TrackJunke

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From: W-S, NC

You should have it checked out, detonation is not good at all.

Apr 29, 2003 | 03:40 AM

Jeff Curtis

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From: Virginia Beach, Va.

Alex, what are we calling "detonation"??

I'm guessing you may be referring to small backfires when changing gears in a "spirited" fashion??

If so, the "cup pipe" may be suspect as when installed, often they don't seal up the same as your factory components...causing small areas where cold air can be ingested into the hot exhaust system during periods of decel (in between gears and downshifting).

NOW, if you are in fact experiencing spark DETONATION...that, my friend, is NOT a normal issue and is a BAD thing! <img border="0" title="" alt="[Eek!]" src="eek.gif" />

Please determine if you are referring to spark detonation (ping/knock) or small backfiring.

Apr 29, 2003 | 04:44 AM

rutz964C4

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Racer

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From: Madrid, Spain

<blockquote>quote:<hr />Originally posted by Jeff Curtis:
Alex, what are we calling "detonation"??

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Apr 29, 2003 | 08:32 AM

John Boggiano

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John, nice to see you have retained your sense of humour in view of your current problems.

Then again, maybe your hassles make you think of war!

Apr 29, 2003 | 10:54 AM

#10

Pietro

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From: Munich

one "possibility" is that a throttle switch is faulty. This may give you a "too rich" mix in deceleration and too much fuel in the exhaust which in turn may "detonate". This would happen independently if you actually change gears or not, it should also happen if you decelarate at a traffic light with the gear and clutch engaged.
ciao
Pietro

Apr 29, 2003 | 11:10 AM

#11

joey bagadonuts

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From: Highland Park, IL

Yes, I have a cup pipe and get the occassional "pop" when shifting. I can usually encourage a louder detonation by leaving my foot on the accelerator for an extra second as I press the clutch pedal. Sound familiar? Also, the sound was not there prior to installing the cup pipe.

Further, when I cut my airbox open (similar to the Cup airboxes sold by Fabspeed and others), the popping volume diminished and was less frequent. I mention this because Pietro's comment suggests a fuel mixture link which I think is possible. Cutting the airbox seems to have affected this mix as well.

Disclaimer: These are just my observations and not intended as remedies or tuning recommendations.

Apr 29, 2003 | 01:55 PM

#12

Ade - C4 91

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From: New Zealand

Ha! I like your disclaimer Joey, we can tell you live in the US

Ade.

Apr 29, 2003 | 05:56 PM

#13

anewbill

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From: Fort Mill, SC

I to have a cup pipe and experiance small backfires during periods of decel in between gears and downshifting. It is most noticable in the morning before the car has warmed up. Is this harmful to the engine or any other components?

Apr 30, 2003 | 02:52 AM

#14

Jeff Curtis

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From: Virginia Beach, Va.

OKAY!! SO, we seem to all be in agreement that our "Cup pipe" clad 964s will pop upon decel.

...now let's take a moment to sit down in a circle and sing "Kumbaya". <img border="0" alt="[hiha]" title="" src="graemlins/roflmao.gif" />

Now that's what I call getting to the bottom of something.