Tin Indian

Every once in a while someone will post that they believe they are getting blow-by from the rings, even to the point of pressurizing the crankcase.

There is a good check that can be easily made while the engine is idling.

You will see a rubber hose attached to the upper pass. side of the throttle body. This is the fresh air inlet tube for the PCV system. Filtered air is drawn in this tube to the valvecover and crankcase area by the PCV valve (located in another tube).

Unhook this tube while the engine is warm and idling. Put your finger over the end of the hose so no air can be pulled into the hose and crankcase. Let the engine idle for about at least a minute. Keeping your finger over the hose, remove the oil fill cap. You should hear lots of air wooshing into the plastic filler neck that the fill cap screws into. This is because the PCV valve is creating a suction in the complete crankcase area. This negative pressure will continue to build in the crankcase as the PCV vacuum depressurizes the area over time.

"Blowby" due to poor ring sealing at idle will not allow a vacumm to be built up in the crankcase during this test.

NOTE: Some ring sealing problems can occur during high RPM operation. This test will only tell whether or not the rings are leaking pressure during idle, however, it seems that cars with suspected blowby problems will fail this test miserably.

NOTE: If the car fails this test, first make sure all other PCV hoses are properly connected and that the PCV is operable and drawing a vacuum in the valve covers/crankcase.

Hope this helps someone,
Ron

NOTE: This test does not replace an acurate cyl leak down test, but is a very good indicator.

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<small>[ March 15, 2003, 11:25 AM: Message edited by: Kimchee and Rice ]</small>

Tin Indian

Just for your info >

You will also see a hose that attaches to the neck of the intake manifold on the pass. side (just below and to the rear of the tube we unhooked on the test above). This tube is where the PCV valve is attached in-line. Crankcase gasses are pulled into the intake at this point by vacuum. These gasses are actully being pulled from both valve covers due to a rubber "splitter" tube that attaches just downstream of the PCV valve.

I other words, crankcase gasses are pulled under vacuum through separate tubes that attach to the rear section of each valve cover. These 2 tubes are then joined togather at the rubber splitter. The gasses then are sucked through a single tube, through the PCV valve and then into the pass side neck of the intake manifold as discribed above.

The tube we un-hooked above just provides a fresh air inlet to the crankcase. This tube again attaches to the TB and the upper front of the pass. side valve cover. There is no vacumm created by the TB at this point. This air inlet is actually in front of the throttle plate. Basically plumbed there so clean air from the engines air filter (in front of throttle plate) is sucked into the crankcase.

Really a fairly simple system that has been in use since the 60s. My old 69 Ply Road Runner also had a PCV system. Only real difference is that the Ply motor sucked air from just one valve cover and not both, as in the LS1. Accomplished the same thing though.

End of PCV 101 lecture <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

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<small>[ March 15, 2003, 11:13 AM: Message edited by: Kimchee and Rice ]</small>