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diagnosis please (long sorry)
I have an 85 euro carrera with 75k on the clock. A few weeks back it started slightly dropping off on power beyond 5500 rpm. It was due for a major service so I did a valve adjust, plugs, plug wires, fuel filter, oil change. When I was rotating the crank for the #4 cylinder it felt fairly light on compression, so I did a compression test. #4 was at 110 psi. Then I did a leak down. 50%
 I wanted to see if I could hear where the leak was so I put some air directly into the cylinder using the compression test hose. Here's the kicker. I could HEAR the air escaping though the fan shroud. Not though the intake or the exhaust. So I'm guessing it's coming from the top(intake side) of the head where it meets the cylinder. I then retorqued the head studs (none of them took tourque) and retested, same result. The motor has an intermitint(sp) mis at idle, but the power seems fine on thottle up to 5500 rpm. I haven't done any money shifts but have dipped a little into the redline at the track to make a pass every once in a while. Before I start tearing the motor down for some exploration, does anybody have any clues? I'm at a loss. Thanks in advance for any advice. Last edited by mackpipes; 12-23-2003 at 01:50 PM.. |
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12-23-2003, 01:48 PM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,050
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Sounds like broken headstuds, but I would have thought you'd have realized that when you retorqued. Hopefully it's not as bad as it sounds.
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa  SOLD 2004 - gone but not forgotten
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12-23-2003, 01:54 PM
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masraum,
All the head studs were in tact and tourqued to spec. |
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12-23-2003, 01:58 PM
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Registered
Join Date: Jun 2001
Location: Sweden
Posts: 5,911
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Cracked intake valve? You can hear hissing sound trough fan even if air is just escaping into intake...
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Thank you for your time, |
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12-23-2003, 02:04 PM
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Back in the saddle again
Join Date: Oct 2001
Location: Central TX west of Houston
Posts: 56,050
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could you hear the noise behind the flapper after taking out the air filter, or did you try that?
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Steve '08 Boxster RS60 Spyder #0099/1960 - never named a car before, but this is Charlotte. '88 targa SOLD 2004 - gone but not forgotten
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12-23-2003, 02:07 PM
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I'm using a cone filter in place of the airbox. I didn't take the filter off to listen because the sound was so prevalent though the fan. I'll give that a try.
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12-23-2003, 04:22 PM
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Sounds like it could be a valve. (Cracked, bent, or just too tight.) I would also check your intake valve clearance on #4. If the recent valve adjust got it too tight, the valve would leak. THis could also burn the valve, causing larger issues!
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Chris ---------------------------------------------- 1996 993 RS Replica 2023 KTM 890 Adventure R 1971 Norton 750 Commando Alcon Brake Kits |
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12-23-2003, 06:18 PM
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Now in 993 land ...
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Did you adjust the valves with the plugs out of the heads? I know, gravity goes the other way, but may there have been carbon buildup caught in the valve, leading to a bad adjustment?
Just a (much cheaper) thought. George |
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12-23-2003, 06:30 PM
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I had thought about the carbon in the valve seat. After I tried retorquing the head studs I ran a tank of techron thought it in hopes of an easy fix. But it still leaked. I'm going to go back and check the valve clearance. I hope it's as simple as me screwing up a simple valve adjust.
 Thanks for all the input. Happy holidays.
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12-23-2003, 06:57 PM
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Now in 993 land ...
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Ted:
Always try to find the easy and cheap solution first.  Good Luck!George |
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12-23-2003, 08:16 PM
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1970 Porsche 911 S 
