Engine bay pics and questions - P38 inlet manifold and LPG

Comments on breathers and relocating.

I NEVER do it for D1/RRC engines. They have a simple breather system that only loads fumes into the intake area, the fumes are less explosive than the gas/air mixture that is there too. I have no trouble this way. I have done dozens of these things.

I ALWAYS do it for P38/D2 engines as they have a positive crankcase ventilation (PCV) system. The breather connected to the throttle body MUST be reconnected to the clean side of the mixer so that gas/air (read EXPLOSIVE) mixture is not sucked into the crank case. Failure to do this can cause the sump/rocker covers to split if the gases in the sump are subject to an ignition source.

Neither breather connection is the cause of a back fire, only the consequences change. Electrics are the root cause of most backfires, leaky head gaskets and carbon deposits being the other most common causes.

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Originally Posted by bee utey

Comments on breathers and relocating.
I ALWAYS do it for P38/D2 engines as they have a positive crankcase ventilation (PCV) system. The breather connected to the throttle body MUST be reconnected to the clean side of the mixer so that gas/air (read EXPLOSIVE) mixture is not sucked into the crank case. Failure to do this can cause the sump/rocker covers to split if the gases in the sump are subject to an ignition source.

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Thanks bee utey. Great info. I cant quite work out how to plumb a new connection for the breather house into the round air inlet tubing. Is there any standard way of doing this?


Secondly, today for the first time, I could smell LPG after the engine stalled when on LPG. Normally it never stalls. Last night I did install a hot shower heat exchanger in line with the LPG heater hoses. But I did very little work indeed on or near the LPG converter unit. I would be very surprised if I have upset any connections to it. If the heat exchanger has somehow reduced coolant flow to the LPG converter, could that cause the smell? I did notice that the LPG converter unit was cold and had water condensing on it, like the metal aircon hoses do sometimes.

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Originally Posted by glenhendry

Thanks bee utey. Great info. I cant quite work out how to plumb a new connection for the breather house into the round air inlet tubing. Is there any standard way of doing this?


Secondly, today for the first time, I could smell LPG after the engine stalled when on LPG. Normally it never stalls. Last night I did install a hot shower heat exchanger in line with the LPG heater hoses. But I did very little work indeed on or near the LPG converter unit. I would be very surprised if I have upset any connections to it. If the heat exchanger has somehow reduced coolant flow to the LPG converter, could that cause the smell? I did notice that the LPG converter unit was cold and had water condensing on it, like the metal aircon hoses do sometimes.

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You may have introduced an air lock into the LPG water hoses. Then the LPG will chill the converter and you will smell the excess gas evaporating. Run the engine at about 2000rpm until the converter is warm to touch.

The normal way to connect the breather is for the mixer attatchment to have a fitting that connects through to the clean side of the mixer. Your mixer that you pictured earlier has this fitting which vents into the space in front of the gas ring restriction:

http://www.aulro.com/afvb/attachment...t-imag0423.jpg

Remember posting about the oil??? It probably comes from there.

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Originally Posted by glenhendry

Hi All
Exhibit B shows a plug in the inlet manifold which doesnt appear to be connected to anything. The plug is quite loose and I cant seem to tighten it. Anyone know what it is for?

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PhilipA is correct, this second plug (with the red trim) is for a brake booster vacuum hose, not used on our P38s. Here is the link to the part.

you mentioned in your first post that the brake booster port is loose? Maybe it's sucking in air, making it run lean thus your backfiring.