If the CEL is due to the valve the code should be 1123.
Yep... my mistake... just rechecked my diagrams. Good point. So we need a new theory. What is the bypass system doing to the main cats which would trigger the 1211 codes?
Assuming it was generating a 1123 (bypass solenoid valve) code, you're saying you couldn't use a diode or something more sophisticated to fool the LH ECU into thinking everything was behaving normally? Maybe you could even piggyback an additional vacuum solenoid on top of the OEM one? (if you didn't have the issue of the Capristo using vacuum to close the valve)
on my 2.7 Installed a new Capristo Bypass Valve (the OEM one did not hold vacuum and looked like it stayed close) and 200 Cell Cats. After about 10 minutes of driving I get CEL on both 1-4 & 5-8 and they seem to go off and right back on. Never had a CEL with the previous setup = test pipes and OEM valve so I did buy some replacement thermoprobes but looking at this thread it seems like it is the Capristo Bypass Valve. I don't hear an audible change from low to high rpm so it may not be closing and throwing a CEL code?
Did you change the solenoid valve, too, to a Capristo solenoid valve? The Capristo works in the opposite sense to the old exhaust: Vacuum = valve closed, not valve open (OEM), so needs a different type of solenoid valve. Or you had a vacuum issue in the first place. Low vacuum? Leaking pipes. If you suspect a vacuum issue, check all your pipes and one way valves: Image Unavailable, Please Login Image Unavailable, Please Login Here's an example of someone with a vacuum issue: https://www.ferrarichat.com/forum/posts/149138257/
Original valve would not hold vacuum when tested directly (attached pic/basically it loses pressure quickly from 15 to 0 psi in about 15 seconds so I add assumed valve was failing and didn't look for other causes). Capristo solenoid valve installed and double checked. One of the hoses into the T-fitting looked loose/not a tight seal so I did put some glue for a more air tight seal. Still no difference maybe I should clamp it with a stainless fitting. I just ordered 2x of the one way check valves (the black/white one close to the engine) so hope that will help Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Check the connections to the metall pipe (part# 145155) on both sides closely. There is no need to use glue or stanless steel fittings. The nippels of this metal pipe can break... mine did that ( a workshop messed this up on an engine out a couple years ago) and visually i could'nt see the micro crack. Found the crack, or better could hear it, when i tested the pipe separatly Cheers blox
I had a similar issue which was caused by either a hairline crack in a vacuum can nipples or a leaky secondary air pump solenoid. I assume the latter was the main cause and I probably damaged the vacuum can nipples while investigating. Thread here: https://www.ferrarichat.com/forum/threads/vacuum-reservoir.684662/#post-149396033
Also, you could try to run a length of vac hose from the solenoid directly to the valve to see if the connections to the metal pipe, or the pipe itself, are leaking.
