All you V11 Sport/Lemans guys.... Why the backfiring?

[ritratto]

Hey everyone.... My '03 Lemans just recently started backfiring when I throttle down. Whether high or low rev, seems to make no difference, except how loud it is. If I pull in the clutch, it stops, but would feel better if it stayed under power instead of free-wheeling.

What happened and can it be fixed?

Stock exhaust system... nothing fancy going on here. Help!

[Vasco DG]

Air leak in the exhaust somewhere. Does it have a front crossover that loops down under the alternator cover? Is this loose?

Pete

[rocker59]

I'd check the front crossover for leaky gaskets at the joints with the headpipes.

[jomarti3]

We had a crack in the front crossover area on a 2004 LeMans.  Fixed, happened again.

[rocker59]

We had a crack in the front crossover area on a 2004 LeMans.  Fixed, happened again.

Best thing to do for that problem on the '03/'04 Sport/LeMans is replace the headers that delete the front crossover.

[ritratto]

I got some billit aluminum gaskets for the crossover pipe from MPH and fitted them about a year ago and no known leaks there any longer. Crossover is tight. Is there another culprit?

[rocker59]

I got some billit aluminum gaskets for the crossover pipe from MPH and fitted them about a year ago and no known leaks there any longer. Crossover is tight. Is there another culprit?

Check the exhaust gasket at the head, and make sure the nuts are tight on the retaining collars.

Otherwise, I'd be looking for cracks in the system.

 

[Vasco DG]

Yup, air leaks are the commonest cause. Check every joint in the system and then go hunting for cracks.

Pete

[ritratto]

Thanks guys... will have another look over it all tonight!

[pauldaytona]

That "billit aluminum gaskets for the crossover pipe" make that it is tight, but also inflexible, and since the heads dance their shaking dance, chance is that there comes a crack in the stainless pipes. Now or later

[Unkept]

Intakes rubber cracked or loose?