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loud Popping Sound - Please Help !!

  #1  
Old 07-03-2007, 12:58 AM
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Default loud Popping Sound - Please Help !!

Hi, am new to this trend and wondering if i can get some help. I have a 83 930 Turbo that runs on a bigger turbo and intercooler and a Autronic SMC stand alone computer. All this done by the previous owner. Most recently, i retuned the car as it was running too rich and was really happy with the power delivery until i started to downshift, the exhaust explodes witha very loud popping noise (somewhat like backfire). Any idea how to get rid of the noise??These are some feedback that igot..

1)could it be that the exhaust is straight through and rather short cos the engine is at the rear??
2) The injectors are too large (previous owner changed it)

Appreciate your comments.. Thanks
 
  #2  
Old 07-03-2007, 07:16 AM
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Default RE: loud Popping Sound - Please Help !!

Where are your AFR's at. I am guessing you are leaving some unburnt fuel in the exhaust on the downshift, then it ignites in the hot exhaust. Probably shoots a bit of a flame too
 
  #3  
Old 07-03-2007, 08:38 AM
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Default RE: loud Popping Sound - Please Help !!

Hi Doc !!!

ARF's at -13.1 at 2000 rpm and drops to -11.1 at around 4000rpm and -11.4 at 5500rpm at dips back down to -11 at 6000rpm ... is there anyway to make the car burnt those drips of fuel before getting into the exhaust? Man.. its really rude when it pops.. its like a loud fart!!! and porsches dont fart!!! they roar !!!! .... in anycase, any idea doc??? can the car run any leaner??? and yes, it throws out flames ... :-)

ninty
 
  #4  
Old 07-04-2007, 04:45 PM
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Default RE: loud Popping Sound - Please Help !!

hey doc, what does AFR stand for?
 
  #5  
Old 07-04-2007, 07:37 PM
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Default RE: loud Popping Sound - Please Help !!

Hi Panzer,

AFR - Air Fuel Ratio ..
 
  #6  
Old 07-05-2007, 06:13 AM
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Default RE: loud Popping Sound - Please Help !!

Don't know your particular engine management system but you needto tune it to lean it out under decel.
The numbers you gave above are steady state or accel, right? The condition you're describing is at high RPMs with the throttle closed, or decel. Another possibility is a wastegate (or boost controller) that's not bleeding off boost under decel. By keeping up boost pressure under decel, it can be tricking the computer into taking its fuel numbers from a cell in the load (high manifold pressure) region, rather than the decel (low manifold pressure) region of the fuel map.
 
  #7  
Old 07-05-2007, 07:55 AM
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Default RE: loud Popping Sound - Please Help !!

hi wdonovan,

thanks for the advice, will be seeing the tuner this sat and will share with him what you told me. keep you posted.

ninty
 
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