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Author Topic: MOTOR DECOMPRESSES plzhelp LXman25thANNV. ¯ Member # 5359 posted                              After installing a edelbrock lower and uper intake the motor will make a "decompressing sound" like its relieving pressure after i turn the car off. It runs perfectly and I am pretty sure there is no vacuum leak. What could be wrong???? Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : JohnB Tech Moderator Member # 969 posted                              You have a manifold leak; it is either at the head surface or upper to lower intake surface. Sounds like air blowing off, correct? maybe a slight whistle to it? -------------------- 1965 Shelby Cobra 1993 Cobra 2012 F150 Raptor 2020 GT500 Posts: 6523 | From: Orlando FL/Redding CA | Registered: Mar 2002  |  : LXman25thANNV. ¯ Member # 5359 posted                              yes,but it only does it right after i turn it off. could it be anything else? like maybe the pvc valve? or vavles that arent working correctly? it doesnt leak while its running-its almost like there is pressure building up in then moteor Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : BlackNGold CaliforniaFords.com Moderator Member # 655 posted                              Does this happen even when the car is warm?.... -------------------- -SLOWER TRAFFIC KEEP RIGHT- Posts: 5132 | From: Bay Area, CA | Registered: Dec 2001  |  : LXman25thANNV. ¯ Member # 5359 posted                              It only does it right after i turn the motor off. it could run for a only a sec or an hour and it will still do it. Could pressure be building up when the motor runs because of a bad pcv valve or something else??? does the manifold just run at a hegher pressure? I used the stock pcv valve even though the hole was alot bigger..good'ol duck tape Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : AJBlackGT ¯ Member # 3936 posted                              Thats how a motor makes power, it buils pressure in the cylinders. You have pressure leaking from the cylinders somewhere it sounds like -------------------- 90 Notch Posts: 1896 | From: Sacramento | Registered: Dec 2003  |  : LXman25thANNV. ¯ Member # 5359 posted                              ................its not the cylinders-im not a total morron....but thanx for the idea Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : Fostang ¯ Member # 3752 posted                              If it aint broke don't fix it. [ February 19, 2005, 11:19 AM: Message edited by: Fostang ] -------------------- 67' Fastback TT 408 67' Camaro Lsx 64' Corvette Fuelie 57' Chevy Bel Air Lsx 68’ Pony Convertible 66’ Pony Coupe Posts: 3012 | From: Stockton/Danville | Registered: Nov 2003  |  : AJBlackGT ¯ Member # 3936 posted                              Yeah but the pressure left in the cylinder will leak back past an open intake valve when you stop the motor and it will make that sound... -------------------- 90 Notch Posts: 1896 | From: Sacramento | Registered: Dec 2003  |  : LXman25thANNV. ¯ Member # 5359 posted                              "if it aint broke dont fix it"........ what would that mean?-if it is leaking back out a valve? and why only after i install the manifold? Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : CDT ¯ Member # 5004 posted                                 try disconnecting any vacuum lines going to the climate controls.. -------------------- Custom Dyno Tuning 510.331.0608 Home of Flat Fee Tuning For All Cars, Trucks and SUV's, EFI & Carb, SCT, AFR, Dynatech, STS Turbos, N2O Refills Posts: 1053 | From: Hayward | Registered: Nov 2004  |  : LXman25thANNV. ¯ Member # 5359 posted                              really? why? Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  : RedBaron ¯ Member # 4361 posted                              Could be that your new "Chicks dig me" manifold is letting you hear a sound that the O.E. setup didnt- let's take stock: 1: How is your car running after the upgrade? 2: If #1 is 'BETTER!' or equivalent, maybe you might just let it be? A car with a manifold leak will let you know without a doubt- and, as you know, the piston that is moving on a compression stroke AFTER you turn off the key still has built compression, and that pressure has to go somewhere. I think you found out just how much noise suppresion the stock intake tract has built into it. Either way, just remember that the Honda guys pay big bucks to get the 'PSHSHSHSH' sound that you got for free, so cheer up!! -------------------- 1988 4i coupe, 88 gt 85 ttop- Posts: 830 | From: S.S.F. | Registered: Apr 2004  |  : RedBaron ¯ Member # 4361 posted                              Oh, and to answer your question to CDT, he's trying to help you eliminate the vacuum bleedoff at the vacuum reservior to the A/C unit- check valves go bad, and a reservoir takes it's sweet time bleeding off 25 inches of stored vacuum!! -------------------- 1988 4i coupe, 88 gt 85 ttop- Posts: 830 | From: S.S.F. | Registered: Apr 2004  |  : sic70stang CAFords OG Member # 4347 posted                              i have a trickflow upper and lower and after installing it the car whistles and makes a air sound when u turn it off. my vac is at 22-20 and the motor runs fine. i e-mailed trick flow and bbk (i put a 70mm tb) and they both told me that its sometimes normal for this to happen. i had a friend with the same setup and his had the same sound but a lil louder. -------------------- The anti-crew 1987 rolling safety violation. Posts: 6943 | From: California | Registered: Jul 2005  |  : LXman25thANNV. ¯ Member # 5359 posted                              It probably is normal then, i was just curios if any one else had that prob. thx for all the info. Posts: 40 | From: Chico,CA | Registered: Feb 2005  |  :

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