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exhaust rattle
i have a 87 951 and at about 2900-3200 rpm there is a very significant rattle/buzz from the middle of the exhaust. could this be a broken cat? let me know what you guys think
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12-23-2010, 03:10 PM
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Bet it's the heat shield on the cat!
When cats fail, they spit out chunks of charcoal which rattle around in the muffler/exhaust. It sounds like rocks in the muffler... The heat shield is more of a buzzing noise...
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83 944 NA - Black on black 86 951 - Red - SOLD 7/21 16 Ford Expedition He who hesitates is lost. |
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12-23-2010, 04:18 PM
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your average wrencher...
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x2 on the heatshield theory...
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1982 931 *project* 1986 951 Garrett turbo, Rogue Tuned (sold  )1987 944S chipped, konis, rollbar (traded) 1979 924 total rebuild and blueprinted (sold) |
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12-23-2010, 06:00 PM
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Another theory is:
It could be the gasket is loose between the cat and the muffler connection right about middle of the car. Check the three (3) bolts/nuts holding this together. Sometimes they come loose and cause this rattle. Ask me how I know this fact? Ha. Good luck. 
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Ed Paquette 1983 911SC 1987 944S 1987 944 Manual (Donated to the Nat. Kidney Foundation) 1987 944 Automatic (Recently sold to another Pelican) Last edited by TibetanT; 12-23-2010 at 08:45 PM.. Reason: three bolts not two |
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12-23-2010, 08:41 PM
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Forgot to mention this earlier:
This gasket...some call it the donut gasket since it looks like a donut when removed. Really cheap fix too and should be changed every 50-60 thousand miles anyway.
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Ed Paquette 1983 911SC 1987 944S 1987 944 Manual (Donated to the Nat. Kidney Foundation) 1987 944 Automatic (Recently sold to another Pelican) |
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12-23-2010, 08:42 PM
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Join Date: Apr 2010
Posts: 3,003
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If you are pulling it apart make sure to really get the cap end bolts and the accompanying 12mm nuts cleaned and really soaked in penetrating fluid of your favorite type. I can't tell you enough how annoying it would be to have one of the upper ones strip. when you get them off throw them away and get new ones. M8.
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12-23-2010, 09:11 PM
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Join Date: Jun 2003
Location: Fresno, CA
Posts: 7,779
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I had a very annoying exhaust rattle that only showed up at around 25oo rpm and only when the engine was under load (ie., driving). I could not make it happen in the garage.
I searched and searched but could not find any leaks and everything was tight. Eventually, I had a flex damper (automatic) repair which required removing the exhaust. At this time I replaced all gaskets (including the doughnut). all gaskets looked ok but replacing them cured the rattle. It never did sound like a leak but more like a rattle. Just my $0.02 |
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12-23-2010, 09:29 PM
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Join Date: Oct 2009
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Chiming in a little late here, but you're describing the exact same symptoms I had. Very "tinny" rattle in a very narrow RPM window. Mine rattled regardless of in motion, static, under load... Easy replicated in the garage with my wife at the controls and me poking around trying to narrow down the source.
Mine (89 N/A 944, btw) was the CAT rattling a piece of dislodged "honeycomb" inside. Took it to a reputable exhaust shop in town, and $250 later she was all fixed up. Runs and sounds like a completely different car. Disintegrating CAT must have been pretty restrictive as she now pulls consistently stronger through all revs and all gears. Rumbles a bit louder now that she can actually breathe too. Good luck in your gremlin hunt!
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'89 944 N/A |
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12-27-2010, 03:03 PM
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My 951
My 83 NA
1986 Porsche 944 turbo
1983 Porsche 911SC Targa
Eggplant
