Root Causes of High Crankcase Pressure

Root Causes of High Crankcase Pressure

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Oil being blown out of seals, gas blowing through the oil fill cap or dipstick tube, and oil burning through the exhaust? Here's what you need to look for in the GM 1.4L Turbo.

Root Causes of High Crankcase Pressure

The 1.4L Turbo LUV/LUJ engine has a few potential root causes related to high crankcase pressure. I get phone calls for this issue every week, and I'd like to address some of those root causes in case someone comes across this article in search of a solution to their problem. To begin, I recommend reading this article to help better understand the logical flow of PCV gas through this engine: There are three basic root causes for excess crankcase pressure: PCV system obstruction,, mechanical fault, and intake manifold check valve failure.

PCV System Obstruction

This is the most common source of this issue. Usually, these engines operate normally under idle, but once the owner takes the car out for a drive, they may come back to find oil all over the engine bay, oil burning through the exhaust, and upon removing the dipstick or oil fill cap (at idle), may find gas being blown out of whichever hole was opened. Under normal driving conditions, the PCV system should have a free-flowing path from the crankcase, through the valve cover, the cylinder head PCV port, the intake manifold, the PCV pipe, and finally the check valve at the turbo inlet, before being returned to the turbo inlet. There are two common sources that can cause obstructions in this path.
  1. Use of aftermarket valve covers. I won't name brands here, but I will say that I have had reports of this come back for every aftermarket valve cover I am aware of. I've seen a high rate of failure. I'm not entirely sure why it happens, but either immediately on installation or within the first week of driving, the valve covers fail prematurely and cause an obstruction/restriction in the PCV system. This obstruction causes excess crankcase pressure to build, and when it has nowhere to go, it will find the easiest path possible; usually the valve cover gasket, the front crank/main seal, and the crankshaft position actuator solenoid valve seals. The fix for this is to replace the valve cover with an OEM unit, and I always recommend using only genine GM/ACDELCO valve covers on these engines.
  2. PCV deposits. Related to my article on the importance of oil quality in the PCV system, there are two locations on these engines where PCV solids and liquids (oil, condensation, fuel, and combustion byproducts) can accumulate and settle over time; the PCV port on the cylinder head downstream of the valve cover (toward the firewall) and the intake manifold PCV port. I've had a calls come in for help diagnosing high crankcase pressure where an OEM valve cover was used, to find that these areas were completely blocked off with hard PCV deposits. To check for this, remove the valve cover and check the PCV port toward the firewall side of the engine on the intake manifold, and ensure it is free and clear. If cleaning is required, it is recommended that the intake manifold be removed (or at least separated) and cleaned, as that will certainly also contain deposits.
  3. Stuck/frozen check valve at the turbo inlet. The PCV pipe that goes from the intake manifold to the turbo inlet has a check vlave at the turbo inlet terminal side. If this check valve freezes due to condensation in the winter, it will block all PCV gas flow.

Cracked Piston Ring Land

I know this is not what people want to hear, but it is a possible - albeit uncommon - failure point on these engines. High oil consumption, low octane fuels, and any other conditions that create knock and LSPI (usually reserved for turbo gasoline direct injected engines but also possible in the previous generation 1.4L Turbo) can cause piston ring land failure. In this failure, a chunk of the piston ring land actually separates from the side of the piston. This will cause excessive amounts of blowby gas to pass through the piston. To diagnose, a compression test is required. If one cylinder is significantly lower on compression, it is very likely you have a cracked piston. The best way to check this is with a compression test. During a compression test, actual values are not important, but rather that they are consistent across all cylinders. 

Intake Manifold Check Valve Failure

This is likely the reason you've arrived to this site. The intake manifold check valve has a 100% failure rate. Furthermore, it is being reported that the check valves crack on the back flap on aftermarket manifolds, and the check valves deteriorate on the OEM manifolds (even if the nipple is visible from the top of the PCV port). If you've exhausted all other options

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