Felix.

The rocker cover breather hose (not on a scoob). Does this need to operate under a vacuum or is it just simply allowing air to circulate?

The reason being is on a Seat Alhambra converted to run on LPG. I’m experiencing occasionally backfires which blows the pipe work and air box off. I’m thinking of putting an open T piece in the breather hose to allow the increase pressure to escape.

Jolly Green Monster

iTrader: (4)

the backfire or misfire you mention will be coming back through the inlet manifold and throttle body not the rocker cover breather so you will not solve your problem.

You can vent breathers to atmosphere but you couldn't do that with a T as then the air would be sucked through it unfiltered and unmetered into the throttlebody. The ecu is mostlikely maf based and needs to meter the air coming in to know how much fuel to inject.

but regardless it should not be misfiring like that.. get it set up properly..

Simon

Felix.

It has been running fine with the only problem being it’s a bit juddery when it travels with out accelerating. I put this down to possible ram air into the air box. I therefore took the inlet pipe off the air box which made the running a lot smoother. Only problem now is I’m experiencing the backfires.

I am just wondering if this would this be rectified by a blow back valve or placing an open pipe in the breather system to allow the pressure to escape – or am I curing the symptoms rather than the cause.

Jolly Green Monster

iTrader: (4)

imho yes..

please expand on juddery when not accellerating - do you mean when cruising or when decellerating?

Simon

Felix.

Cruising. And not really juddery – just enough to be noticeable and a bit annoying. It does become more affected in high wind which is why I believe it is the ram which is causing it.

The set up is that the air goes into the air box. From here there is a pipe which first allows the air to pass through the mass flow meter. There is then about 2” of pipe before a connection to the rocker cover breather hose. About another 4” and the LPG gas mixer valve is situated. Another 2” and it connects to the inlet manifold. The LPG is therefore sucked straight into the manifold from the valve. The back fire occurs when from some reason the LPG tracks back into the air box, the pressure builds and goes bang. I just thought a release pipe/vale etc somewhere near to the air box or on the rocker breather hose will allow the pressure to escape.

Of course the nightmare scenario would be if the gas pressure built up in the rocker cover itself, bit it seems to prefer the air box at the moment.

Jolly Green Monster

iTrader: (4)

have you not considered that the air filter works in both directions and is doing exactly what you are wanting to do..

when was the fuelling last checked on the lpg?

Simon

Felix.

Good point about the air filter. In that case though, why does the backfire blow this box up?

Its a closed loop system so it monitors itself. i.e it only takes what gas it needs

silent running

I've not read the whole detailed thing on your intake plumbing but to me it sounds like you've got LPG where it shouldn't be. There shouldn't be LPG fumes or whatever they are, in the airbox or anywhere near it. Backfires are one thing. Small explosions in your inlet tract, blowing your airbox off, are another thing entirely LOL

It reminds me of when I was running nitrous a long time ago on my Clio 16v and it blew up the engine on a rolling road. The suspicion was that a lot of nitrous was sitting in the inlet manifold and just at the wrong time a valve opened and revealed some burning charge, which then spread up into the manifold.

Your first problem which you must solve is why is the LPG in the wrong place.