Uneven Running on a V8i

[Wireless]

Uneven running, as the thing ages you put up with a lot.

Today a backfire while on LPG, and would then only run on petrol, but tickover surging and a loud sucking noise, oops!

Found a split vacuum hose, completely disconnected, a large one attached near to vacuum throttle cruise control/on the inlet airpipe just after the gas ring.

So, I think the split hose caused a lean mixture, which backfired on LPG, which blew off the already split vacuum hose AND bent the metal frame K&N Air Filter insert (big bang then), causing it to drop down inside the Airbox.

Straightened out the K&N, refitted it, and wrapped the Vacuum Hose with Self-amalgamating tape to seal, then refitted.

Runs sweet now, no uneven running either.

Anybody with an uneven tickover, even a slight one, and may have suffered for years with it, check the big vacuum hose that pushes onto the inlet airpipe near the vacuum operated throttle - cruise control.  The underside of the pipe might be split, don't know how I missed it!

[andygod]

Sounds like your lucky that your airflow metre is still intact. Haven’t you got an anti backfire flap fitted to your LPG system?

[Wireless]

Anti-backfire flap?

No, it would appear I do not, although I suspect I'd prolly have parts of the engine pass through the bonnet if it was fitted.

Where would such a device fit, and is there a universal one I could retrofit?

[Ogbyte]

ooh! you were lucky there, backfire through airfilter on LPG usually results in either annihilation of the airfilter box and/or killing the MAF meter.

unfortunately i've had the latter on our vectra, but the Disco's have survived except for the pipe from the MAF to plenum chamber splitting from a blowback

the blowback can also happen if you let the LPG run out (again, from experience)  :D  :shock:

Gary

[Range Rover Blues]

You need an anti backfire on a flapper system, many people don't fit them on Hot Wire as they think it doesn't need one.  Many times it doens't.

When blue starts backfiring, it's going through an exhaust valve :roll:

[MartinV8]

I managed to destroy my hot wire MAF due to a backfire, I would say fit a flap to both types, just to be safe!

Martin