Exhaust noise. Sounds like a half backfire???

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KLP 92

MB Enthusiast
Joined
Nov 28, 2003
Messages
2,671
Location
London
Car
Mercedes S600, SL600, C250TD
My 500sl 1982 model has come back from a full service inc spark leads, distributor cap and rotor arm replacement.
I 've had a Longlife exhaust fitted 8 months ago and now i've seem to have a problem. When i start the car i get a slight popping noise from my rear box. Sounds like a half backfire. Then if i accelerate suddenly in gear and let go off the accelerator suddenly i get a popping noise the exhaust.
I'm baffled with what the problem is as its really got worse after the service.
 
screams loose exhaust to me. air gets in the zorst and causes this, irrespective of engine type or characteristics. maybe they ragged it and clipped the pipe? theres no real reason to disturb it is there? or did you have any under body work done - like petrol tank stuff, suspension etc?
 
Sounds like you havnt got enough back pressure to stop unburnt mixture getting sucked out the exhaust valve during the overlap. This unburnt fuel is then igniting in your header pipes due to the heat.

It could be that your exhaust isnt sealed correctly as Guy has mentioned or the long life aftermarket exhaust isnt designed properly for your set-up. Either way, it means your car will be running lean until you sort it out.
 
You say you have had a new distributor and rotor fitted. Has the problem arisen after this work has been done? Could be your distributor is slightly out (Not sure if this would make any difference on your engine) or is the cap seated correctly? Just a thought.
 
It had new rear springs fitted as well.
When i started the car in the morning it sounded like someone was hitting against an empty tin can!. After a few minutes its ok and only gives that sound every now and again. Its strange its only begun after the work i've had done on it.
I took the car down to the exhaust place as it has a lifetime guareentee. they thought it was a backfire at first but then admitted it maybe the exhaust. They are rebooking the car in for a new system.
When i took the car back to the garage that does the work on it they said it shouldn't be anything they done as they just replaced the parts under the engine and haven't tuned it up or done anything else. Also changing the springs wouldn't affect the exhaust. Just a coincidence??
But it only does it when its cold. Strange and it means i won't be driving it till i get it sorted as i know it will bug me.

After i had the exhaust fitted i noticed more power and better economy so no complaints in that department!
 
As already mentioned it could be valve overlap..no change here, it could be an air leak into the exhaust..but no blowing, or it could be ignition timing being retarded. This needs investigating as work has been done on this area. Check the mechanical advance at idle, vacuum disconnected and also check the vacuum advance has been connected properly.
It sounds like the timing may have been setup with vacuum connected, so is retarded.
 
Dieselman said:
As already mentioned it could be valve overlap..no change here, it could be an air leak into the exhaust..but no blowing, or it could be ignition timing being retarded. This needs investigating as work has been done on this area. Check the mechanical advance at idle, vacuum disconnected and also check the vacuum advance has been connected properly.
It sounds like the timing may have been setup with vacuum connected, so is retarded.


But would a simple change of the spark leads and distributor cap and rotor arm cause this? Or could something like a vacuum pipe have been pulled off when installing the leads??
 

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