I've had my 2003 XJR for over 15 years and made several performance mods. About 80k miles ago I had a very skilled machinest make a much larger crankshaft pulley to drive the supercharger over 14 psi. What a kick! But as of late, I've been plagued with excessive oil spray coming through the full load breather and fowling the mass airflow sensor. I first checked the part load breather for blockage or vacuum leakage. The orifice was clean and open and the hose in perfect condition to the throttle elbow. I put the scanner on it and drove it. I observed 14.1 psi on WOT and 4 psi at an idle. I would think the manifold absolute pressure should be in the vacuum range at an idle. Does this sound like a sc bypass valve sticking or leaking? Motor runs extremely strong but slightly imperfect idle. With the oil fill cap off for observation, raising the idle to 2000 rpm produces no crankcase bypass whatsoever. I'm a retired automotive electronics diagnostician so I have sufficient test equipment if anyone has any suggestions. Thanks in advance for any input.

 

The bypass valve does not completely remove the boost from the inlet manifolds but only provides certain relief to the boost pressure by providing a path for the air flow (back into the supercharger) in parallel to the flow to the manifolds. At idle, there is probably a very small boost with the original pulleys but, in your case, is higher because of the much larger crankshaft pulley.

Excessive oil through the breather, if everything else is good in the breathing system, could be due to overboost and some wear of the piston rings and/or cylinders?

 

catch can. problem solved


your intercoolers are due for a cleaning from all the oil mist the FLB kicks out

 

Definitely a catch can as suggested.

You could also clean out the intercoolers with a methanol injection kit. No disassembly necessary.

 

First thing that came to mind was a catch can.

 

Thanks for all your inputs and I also considered a catch can on the full load breather. But only as a last resort if reason isn't economically resolved. I considered ring wear blowby and observed no evidence of that with the oil fill cap removed. Today I tested the bypass valve function. At an idle the valve is fully actuated from vacuum solenoid. With a quick snap on the throttle, vacuum drops and valve deactuates. However at an idle I manually deactuated the bypass valve with a screwdriver and there was no change in the idle. Next chance I get I'm removing the bypass valve and checking the valve plate. Yeah, after resolving the oil contamination I'll need to fog some methanol thru the entire induction system to clean it before it gums up.

 

Bit off topic. But I love when people mod these cars. But yes, I also thought of a catch can.