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Join Date: Sep 2012
Posts: 106
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Why My Engine Backfires?
Why my engine backfires occasionally when going slowly with no throttle, for instance driving downhill?
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07-13-2021, 08:33 PM
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Crotchety Old Bastard
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Are you sure this is a backfire and not the typical burble of off throttle engine braking? Is this 930 new to you or have you recently changed the muffler to something less restrictive than OE? CIS continues to pump fuel when off throttle, that excess fuel can ignite in the hot muffler. Quiet mufflers silence this.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds '78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8 |
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07-14-2021, 06:03 AM
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Join Date: Oct 2006
Location: MYR S.C.
Posts: 17,321
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also check for exhaust leaks at the heads.
make sure intake bolts are tight.
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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07-14-2021, 07:13 AM
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Join Date: Sep 2012
Posts: 106
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Thank you for explanation - makes sense.
No, it was always like this for 8 years since I got the car. I just was not sure what it was. How backfiring would be different? OFF TOPIC, CAUTION: I have similar sound on my Yamaha cruiser (V-twin) which obviously is not CIS. It was not there till now. What could that be? |
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07-14-2021, 07:22 AM
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Registered
Join Date: Oct 2006
Location: MYR S.C.
Posts: 17,321
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air leaks in exhaust most likely
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86 930 94kmiles [_ _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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07-15-2021, 09:38 AM
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78 Porsche 911SC 3.0L, 3.3Turbo soon. 
