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86-C10-V6 · 10-08-2007, 02:46 PM

I think mcpaul is mostly correct however I believe the EFE valve is located on the drivers side and when the engine is cold the valve is activated by vacuum which causes the exhaust gases to pass through the intake manifold and exit through the opposite exhaust manifold.
If you plug the vacuum line, the performance will degrade slightly during cold engine running and you will have higher emissions during that time.
Hope this helps

10-08-2007, 02:46 PM	#5
86-C10-V6 Shadetree Mechanic Join Date: Oct 2002 Location: Youngsville, NC Posts: 100	Re: Help! broke vacuum tree on thermostat housing! I think mcpaul is mostly correct however I believe the EFE valve is located on the drivers side and when the engine is cold the valve is activated by vacuum which causes the exhaust gases to pass through the intake manifold and exit through the opposite exhaust manifold. If you plug the vacuum line, the performance will degrade slightly during cold engine running and you will have higher emissions during that time. Hope this helps __________________ Dave M. (Hacksaw) 86 C10 Scottsdale LWB, 4.3L, Edelbrock 1904, K&N, 700R4, 3.08 Auburn Performance 89 GMC S-15 Extended Cab 4x4, 4.3L, FI 98 K1500 Xcab, 5.7L, 3.43 Gov-Lok