Popping in exhaust

[what hasnt been]

Greetings,

Every now and again I get a popping in the exhaust of my TVR Chimaera 40HC 1996. It is less than a back fire but loud enogh for me to indulge in a worryette. I do know that the exhaust note is reminicant of a Hawker Hurricane but it does seem to be a new sound and quite randon abou when it manfests itself.

1. Any ideas?
2. If you aim me at ignition timing, which is wher eI think the answer lies, please advise as I do not have what I am used to or what the "books" (whether books or internet) suggest and I seem to have an obvious mark on th pulley and a single pointer sticking out with no graduation for BTDC degtrees and such .... so how do I do it?

Regards to all my readership

[ralphy12345]

what hasnt been said:

Every now and again I get a popping in the exhaust of my TVR Chimaera 40HC 1996.

So do I: fantastic, isn't it?

I wish it did it more often, tbh.

R

[blueg33]

I think it cam also be caused by a leak in the exhaust manifold. Air gets in and fools the lambda so the ecu compensates.

I could be wrong but exhaust manifold gasgets would be my first port of call

[.Mark]

Does the pop come from the front of the car? I get the same, from the left bank as far as I can tell, and it's after I've been driving on a flat throttle.

Manifold gaskets are ok though, pretty sure I'd hear the familiar ticking if they were shot?

[anonymous-user]

Mine does pop a bit. The manifold gaskets were done yesterday (only had a couple of very tiny leaks anyway, but had it done for peace of mind) and it still does seem to pop/burble feathering the throttle on overrun

Mine has the full original unmodified system though, pre-cats, main cat and silencers are all in place, so I don't expect any big pops or bangs.

My Focus ST also pops aswell, especially when cold. Not as easy to provoke and a bit more random when it does, however it can give a louder pop than the Chim sometimes, and that has the original system aswell.

[J400GED]

It is possible to invoke popping whilst slowing down by applying very slight pressure on the throttle pedal, so that the car is still "on the over-run" but with very light pressure on the throttle you are introducing excess fuel into the cylinders which isn't burning correctly and igniting later than it should thus causing the popping.

It could therefore be that the OP is leaving a slight pressure on the throttle whilst slowing down, causing the popping at what seems to be random times.

Personally I think it's great fun seeing for how long on the over-run you can keep the popping and farting (oo-er missus) going....

Maybe we should start a competition to see who can do the longest "over-run burble" I was going to say fart but everyone would just take the pss

ETA: Having read through, even "over-run burble" could have different conotations...



Ged

[.Mark]

I think the OP was suggesting a pop inside the exhaust system, pre-CAT's rather than over run. That's why I mentioned my oddity.

J400GED said:

Maybe we should start a competition to see who can do the longest "over-run burble"

In the Cerb I managed this for about 1/2 mile recently, long hard acceleration off a slip road then back off the gas to allow me to come off at the next slip road - with the system I have on that it was amazing and made more so because of the reverbs off the concrete central reservation

[Pondered Scrotum]

J400GED said:

It is possible to invoke popping whilst slowing down by applying very slight pressure on the throttle pedal, so that the car is still "on the over-run" but with very light pressure on the throttle you are introducing excess fuel into the cylinders which isn't burning correctly and igniting later than it should thus causing the popping.

Does this work on all engines...or just big loud ones in TVRs..?

[anonymous-user]

It worked in my Triumph Spitfire and my current Focus ST, so yes.

[Simple]

It works nicely on my chim, even more so since the exhaust was sleeved. Also works on the daily snottier (cooper s).

Simple

[Pondered Scrotum]

Cool...I'll give it a go in the '5 tonight

Cheers!