Quote:
Originally Posted by S81
When you remove the oil cap on the engine i know my car goes of idle ,the chap i know who does a lot of engine work says its to do with it being a positive pressure engine ,i'm sure someone here will know exactly what that means
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Positive Crankcase Ventilation (PCV). It's a bit of a misnomer tbh because intake vacuum is applied to the crankcase to suck out any combustion gases which escape past the piston rings. That makes the pressure in the crankcase negative at low engine load, so I guess it really means 'we definitely are ventilating the crankcase'
The breather pod cuts off the vacuum under heavy load or wide throttle openings, since there is no vacuum to do anything, and high load on the engine seals the rings up more so there is less blow-by to recover.
When you remove the oil cap, you basically allow a load of unmetered air in to the engine via the breather pod, which upsets the combustion because the ecu doesn't know about it and so struggles to compensate.
If you remove the cap and it doesn't affect a bad idle then you have an air leak somewhere. The first place I'd look with this one is the inlet manifold gaskets, since its been off previously. Not sure how complex the vacuum system is on the V10, but thats somewhere else to look.
Also, someone please buy this because the price is verging on me buying it just for the engine and I have enough projects already!
