murphy0409

Hi Guys, Mk1 99 GC 4.0l orvis has negative air pressure in the rocker cover. Sewems to be sucking from the inlet manifold. I've enlarged the front breather (little hole to around 1/4 inch) car is breathing fine now but want to fix it properly. If you offer up the oil cap with the small hole in the breather it actually sucks the cap down then squeeks around it.

Any ideas?

Gee oh Dee

Ok.

murphy0409

Anyone got any ideas as it's taking my 66 and 65 year old parents on a long run on Sunday

freegdr

hugh???

Nor-CalJeeper

Are you saying that the valve cover is pulling vacuum? Its normal and controlled by the PCV valve it is getting the vacuum pull from the intake manifold.

It is so the spent exhuast gasses that get passed the rings get burned in the engine instead of vented to the atmosphere worst comes to worst switch your pcv valve for a new one

murphy0409

Yep that's what I was thinking guess I did not put it over properly it aint just sucking gently if you left the oil cap off it would suck all the local strays in. It's sucking that strong that you're getting a whistling noise from the oil cap and you have to physically wrench it off when it's unscrewed - on the WJ you just lift it up. It seems to be coming from the inlet manifold as if you remove the back pipe from the inlet manifold and put your thumb over both sides there is no heavy suction in the rocker - it's almost as though the butterfly flap on the inlet mouth is blocked - checked and cleaned.

murphy0409

Anyone got any ideas they set off at midnight tonight?

Howler_GT

Check the fresh air intake into the cover, sounds like it may be blocked or restricted.
Fresh air intake should be the other connector on the cover. On our older XJ's its usually up front.