Ferrari Bosch CIS Injection 400/412/512 Idle Adjustment (CO and Air Bypass)

I have used a gas analyzer in the past to set the CO to 1.5 - 2.0 %. That works but mostly I use ear and feel. I like the throttle blades to be about a half turn from closed. I then set the idle speed with the air bypass screws. On dual systems I also use a manometer to insure a balance left to right. I tend to like the set up slightly rich as It feels to me with the gas in my area that the throttle response is better.
If the exhaust access ports are available and you can get a 4 or 5 gas analyzer, that would make your job much easier.
FYI, on the 3*8 versions where the plate is accessible while running, then plate response is a tool as well. while at idle, touch the plate gently, and push down slowly, if the idle picks up, it is too lean. I like it to be a slight drop when the plate is touched. Unfortunately, this can not be done on 400/412/Boxer.

 

My Mondial has a somewhat similar albeit single fi system. Assuming the correct mixture setting, the car should barely idle at 600rpm with the bypass fully closed, and then open the bypass to get get the added rpm to reach the 900 or target idle outcome. If this is not the case one would adjust the throttle stop screw as the variable.

Of course the mixture setting does need the gas analyzer per my manual as well. But your approach of checking for for the fuel flow and a bit of a turn of the mixture screw would get a plausible setting in place such that the car would start. You could adjust in very small increments, like 1/16 of a turn at a time, and see where you get a decent idle and off idle response. As you note, the car runs fine off idle with a wide range of mixtures, most of the fi design is to get low emissions at idle, so a good idle the sign of a well set up system.

It is getting hard to find shps with gas analyzers. The small home mechanic units by Gunson the measure CO are better than nothing. I would tune by ear and response feel, and check with the Gunson as a practical approach to dealing with the setup.

Balancing each bank would appear the added complexity for your dual fi setup.

 

I used a vacuum gauge to balance the vacuum left to right while adjusting the throttle plates and the bypass screws. As for mixture/co/gas adjustment, I weld an extra O2 sensor bung to the exhaust where I want to measure, and use a wide band sensor to set the AFR.

 

These systems do need good air flow to work best, so set the idle at 1,000 or slightly higher, the 900rpm might be a bit low for when eg. the ac is turned on.

 

Ah yes, another consideration. I am sure the system is able to properly function at the lower rpm range recommended.

 

Your question remains though as to why the manual implies the air bypass is "normally closed".

I think that the air bypass only affects mixture at idle, off idle other processes take care of ensuring the correct air fuel mixture. Perhaps the manual is referring to balancing the sides, where the bypass might have some effect on the vacuum pull, but not the mixture? That's the only thing I can think of that would explain the manual language.

(I did alot of work on my late Mondial with KE3 injection, and eventually understood the system and got things running perfectly. But the information to get there was not as clear as I would have liked, especially with my late model Swiss market KE3 system which it turns out is similar to the Testarossa system. Hence sharing my comments even though I am missing your four extra cylinders! Indeed, the injector seals for my car actually interchange with the 400 seals, not the regular ones associated with the normal V8 cars.)

 

The highlighted section is referring to the balance of the two sides. Manometer reading at idle should be equal. Then at 2500-3000 it should be equal. If it is not, then the throttle blade is in need of adjustment not the balance screw. Once that is set and balanced, any further idle speed adjustment should be done with the balance screws and the throttle blades should be left alone. The higher RPM check is to insure the throttle blades are opening equally. This is important to off idle performance.