Vacuum Leak, but only when hot?
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Teching In
Joined: Jul 2016
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Vacuum Leak, but only when hot? I've been chasing this vacuum leak for close to a year now. It's the manifold. When I blast propane around the gaskets I can see the O2 sensors go rich, but fuel trims never really react. Anyway, I replaced the fel pro gasket with a brand new factory intake gasket. I thought I had it, short term fuel trims went negative and after a little driving the long term fuel trims was actually negative, never seen a negative fuel trims since I rebuilt this motor. Well drove some more, and the nasty +20% long term fuel trims came back.
This thing only has a vacuum leak when the engine has been at operating temp for more than 10 minutes. My only theory is that my milled heads are just enough to screw up the manifold fit when they get hot and expand. Other than, the PCV tube to the intake is pretty loud and there's a ton of oil in the intake. It's a truck LQ4 with original intake and PCV system. From what I've read, the PCV on this system is a fixed orifice in the valve cover. Has anyone ever experienced this? I know I should have had the heads intake face milled, that ship has sailed. If anything I'll mill the plastic intake to fit.
This thing only has a vacuum leak when the engine has been at operating temp for more than 10 minutes. My only theory is that my milled heads are just enough to screw up the manifold fit when they get hot and expand. Other than, the PCV tube to the intake is pretty loud and there's a ton of oil in the intake. It's a truck LQ4 with original intake and PCV system. From what I've read, the PCV on this system is a fixed orifice in the valve cover. Has anyone ever experienced this? I know I should have had the heads intake face milled, that ship has sailed. If anything I'll mill the plastic intake to fit.
The oil is soaking the gaskets on the bottom of the intake ports. Add heat and they get soft enough to let in some air it seems. Ive had a couple of oil sucker motors that gave my vacuum griefy under the intake. The solve is to get into the newer style orfice PCV valve. You can add in an orfice droppin or what works best is to get some newer valve covers from an 05+ and use those. If you can stop the oil from getting in and run the newer gaskets I think this will go away for you.
The milled heads aint helping, but ive run some that had been skimmed a few times and they still sealed
The milled heads aint helping, but ive run some that had been skimmed a few times and they still sealed
