Slight backfire on downshift

[lesworth]

Hi all,

I'm getting a slight backfire when changing down from 4th to 3rd and 3rd to 2nd. A friend who was following me recently also remarked on this. I've had a read through Bentley and wonder if this is related to either the deceleration fuel shut off (one function of the idle control switch I believe) or maybe the volume air flow meter.

I dont regularly calculate my MPG but I'm sure this must be affecting fuel efficiency. Has anyone had this issue and been able to resolve it?

Thanks,

Les.

 

[Geoff_Fields]

If you get backfire on overrun then likely causes are throttle valve syncronisation and adjustment of micro switch. Needs to be checked by someone with the knowledge.

 

[Dave Wilkinson]

ORIGINAL: lesworth

I'm getting a slight backfire when changing down from 4th to 3rd and 3rd to 2nd.

Les.

Les,

A backfire on overrun is caused by excessive unburnt fuel in the exhaust system. Often caused by reduced backpressure or a leak in the exhaust system. Once you find out what it is make sure you post the details here 'coz most of the Porsche drivers will want to know how they can get it on their car!!!

Since you have a 3.2 I assume you don't have a catalytic converter. Backfires, or, to be more precise, the unburnt fuel, is not good for the cat.


Regards

Dave

 

[Matt P]

I get a back fire from mine when i just rev it when stationary. When i lift off it burbles and pops ,i don`t think its ment to be!
My fuel economy doesn`t seem to good either last weekend i used £50 petrol to get to Mallory Park and back from Chelmsford ( not sure on miles but last year we done it in Transit van towing car and trailer and used about £40 ) so i think i also need to look into things !

 

[lesworth]

I havent changed a thing and this has started happening over the last couple of months..

 

[Beaky]

I have a twin outlet exhaust and mine occasionally does it on downshifts and on very slow/lasy upshifts.

It has done so from the day I purchased it, 3 years and four services, all seems fine and the specialists haven't spoted anything that needs to be fixed

 

[Guest]

Mine has always done it since I bought it but it was very hard to hear with the std exhaust. Now its much easier to hear.

They shouldn't pop if you completely lift off as the fuel is totally shut off, but between gears or on light decelleration they will. Its nothing like a 930 though.

 

[wormand]

I used to get a backfire just after lifting off the throttle in 3rd or 4th during normal driving. I have since replaced the cross-over pipe due to a leak near the joint with the pre-silencer. The backfire has gone and the car seems to drive much better. Can't believe what a slight leak in the system can do to the driveability.