'Puff' sound from engine bay when blipping throttle at idle
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2009-2014 Cadillac CTS-V Performance Mods Discussion, 'Puff' sound from engine bay when blipping throttle at idle in Cadillac CTS-V Series Forum - 2009-2014; I installed an Airaid intake and the dual SMC catch cans within the Airaid box about 5k miles ago. Today ...
  1. #1
    spearfish25 is offline Cadillac Owners Enthusiast
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    'Puff' sound from engine bay when blipping throttle at idle

    I installed an Airaid intake and the dual SMC catch cans within the Airaid box about 5k miles ago. Today for the first time I noticed the engine makes a 'PUFF' sound when I blip the throttle from idle. Also for the first time, I've noticed an air hissing sound from the front of the supercharger, right in the middle by the metal fuel rail. Finally, I've never caught any oil in the can that filters the clean line that goes from the T-connection to the air intake. Pulling that line with the engine running, the part that plugs into the intake is vacuum (disconnect the line from the intake and it's sucking air).

    Any ideas what the sounds are? Have you guys with similar setups noticed any of these things? Should that line really be vacuum at idle? I thought it would feed air back into the intake, not pull it out.

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    The scenario you described at the intake-to-valve cover connection is correct. The connection at the SC snout nipple pulls crankcase air through the other catch can from the valley nipple. This creates a low pressure in the crankcase as air is evacuated. The airflow from the intake to the valve covers provides backfill to the crankcase to maintain a constant flow. You should never have flow from the valve covers to the intake, so that catch can is superfluous.

    For the noises you are hearing, check the lines on the valley catch can. You may have a leak.

  4. #3
    spearfish25 is offline Cadillac Owners Enthusiast
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    Would a leak in the valley can line cause the engine to run rich? I've been having a lot of pops and backfires on decel in 2nd and 3rd gear lately. Otherwise it's running and idling smoothly though. MAF values in Dashcommand seem fine (stable around 3 at idle and rise proportionately to throttle opening). I can't see AFR in the program though.

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    Quote Originally Posted by spearfish25 View Post
    Would a leak in the valley can line cause the engine to run rich?
    No, it would cause it to run lean. And engine braking would cause the highest amount of vacuum, which would suck in more air, thus making it leaner. A too-lean mixture burns slower, which could result in an incomplete burn, which in turn allows unburnt fuel to enter the exhaust system. This could be the source of the popping. Have you noticed a change to the idle since the hissing noise began?

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    spearfish25 is offline Cadillac Owners Enthusiast
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    Hmmm. The idle and overall performance have been totally normal. No stutters, fluctuating idle or power loss. I checked all the hoses and can't find a leak. I do hear some air turbulence at some stainless steel couplings I put in the valley/snoot lines to make catch can removal easier. But they're worm geared at the coupling and I can't imagine it's leaking there. The other places I hear the hissing are in the catch cans themselves and along the aluminum piping that runs around the supercharger, particularly where it has the square split (see pic).

    I've always heard some very low pops on decel but now I occasionally get a true backfire 'pow' if engine braking down through 2nd gear. My exhaust is completely stock and the only changes have been catch cans and an Airaid (no tune).
    Attached Images

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    Da V-Man is offline Cadillac Owners Fanatic
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    The piping you're referring to is the stainless steel fuel line, and the 'square split' is the junction from the fuel pump (top line) to the fuel rail. I can't imagine a hiss coming from there. The snout is right below it. Perhaps that's the source of the hiss. Do you have a short piece of hose about two feet long? If so, shove one end into your ear and move the other end around close to the engine and see if you can isolate the source of the noise.

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    spearfish25 is offline Cadillac Owners Enthusiast
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    Re: 'Puff' sound from engine bay when blipping throttle at idle

    Great trick. Turns out the hiss is audible with the hose-a-scope along the entire length of the valley to catch can. The return hose from can to SC snout is quieter and lower pitch. I have some new hose coming this week and I'll swap it out. Maybe there's a hole in it somewhere.

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