Hi all,
Wondering if I can please pick your brains.

I've just put a new engine including intake manifold into my EL ghia dual fuel.

Since then the car seems to be sucking air from the PCV valve to the LPG adaptor that sits under the ICS. (see photo).



There is no blowback from the engine at all as it's practically new, so this air from the crankcase is being drawn in from the rear rocker cover hose which runs from the back of the rocker cover into the intake piping between the air box and the throttle body.


The other inlet under the throttle body is blocked as it was on the old setup. I tried to copy it exactly but appear to have missed something as now the air seens to be getting drawn in though the rear rocker cover hose by the PCV hose into the throttle body via the adaptor under the ICS. So much air is being sucked in, that I Can sometimes here the pcv valve opening and closing so fast it's like someone is shaking it. (incidently the PCV valve is only 6 months old and metal based one.)

My question is, what is to stop the low pressure in the intake manifold from sucking air though the engine via the rear hose like this? what have I done wrong that would cause this ? or am I missing the point and this is how it's supposed to be?

many thanks

regards

Frank

Any luck Frank?

I have an issue, does the rear rocker cover hose need to be connected to the intake pipe?
I have changed my EL standard piping to metal and of course, there is no outlet for the hose to connect to

Ya kind of missing the point. Air is meant to be drawn through the PCV (positive crankcase ventilation)
It works by manifold vacuum vs: spring pressure, (the spring inside the valve). If there isn't enough blow-by gas it will draw air from the least restrictive place.
At full throttle ei: low intake vacuum the PCV will close and blow-by gases will be drawn out of the rocker cover breather into the intake piping.

On a non LPG setup, I think the rear rocker hose connects to an inlet on the very bottom of the throtle body.

My setup is different because of the LPG, which must mix with air consistently so pipes that can bypass the mixer are rerouted elsewhere. (Or in the case of the rear rocker hose, you wouldn't want it drawing LPG into the engine from under the throttle body so they move the air pickup to somewhere before the LPG mixer.)

cheers

Frank

I have seen whats left of a rocker cover after a backfire when it wasnt done right....

Woohoo was not a pretty sight.....

Thats exactly why the hose has been moved on your car, It doesn't effect the operation.

That adaptor under the ISC is a factory addon IIRC - it was meant to lubricate the ISC plunger with fumes, but looking at the plunger, I don't know if it enhances anything TBH. I wonder if the varying airflow due to the ISC is making the PCV do what you've described, which is normal as Tickford_6 has said.
You can take that adaptor off, and just run the PCV hose back to the tree under the TPS. Main thing is you maintain clean air flow through the rocker cover.

The adapter under the ICS was a restrictor for the PCV - They try and restrict how much air comes into the manifold not via the Mixer ring - it affects mixtures greatly and makes them hard to tune.

Other LPG Mechanics will drill/tap a barb there with a 2mm or so orifice to act as the restrictor instead