355 Explanation of secondary air and vacuum system

The engine itself creates vacuum and stores it in the reservoir/tank (6). The Secondary Air Valve (13) is actuated (only) by the stored vacuum. The vacuum from the tank is routed to the valve via the respective engine ECU-controlled solenoid valve (8).

The pump (40) only creates a positive pressure, not a vacuum. It is not hooked up at all to the vacuum system. The positive pressure is directed to the exhaust manifolds via the Secondary Air Valve and some mechanical non-return valves (22).

The pump sucks up ambient air in the engine bay (and filters it) before sending it to the Secondary Air Valve.

 

That's a bad diagram with, basically, misleading descriptions. Pipe 35 goes to the exhaust bypass valve (from the upper port of the solenoid valve for the bypass valve).

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I think the secondary air valve is simply an on/off valve with no regulation of secondary air pressure. This setup may be capable of pressure regulation, but I think it's simply an on/off action carried out by the solenoid valve (under the command of the Motronic ECU). There are no pressure sensors to sense the pressure in the lines, so no feedback for pressure control.

 

Actually, that diagram I posted is not really a proper representation either (at least not of my '98). On my car, part of the exhaust bypass valve tubing is metal and it is welded to the side of the secondary air tubing (part 36). However, the tubes simply run in parallel and are not connected (air-wise).

 

Mine are black side closest to the throttle bodies. White side goes to the reservoir.

 

Yes, same as mine.

The tank is not the (original) source of vacuum, the throttle bodies* are. Suck on the black side. Blow on the white.

*venturi principle

 

It might be better to say "the throttle bodies and solenoids are both connected to the vacuum tank" (rather than there being different "sides" of the vacuum tank). As Ian indicated, you should be able to blow in the direction from the vacuum tank to the throttles bodies (as that's the direction that the air moves when the throttle bodies "suck" on the vacuum tank).

 

OK, Grant.

1. On your car, the engine provides the source of vacuum while it is running. That is because the piston moves down while the intake valve is open and it sucks air into the cylinder thereby providing vacuum.
2. That vacuum is maximum at idling because the throttle plate is closed. Vacuum is at its minimum when the throttle is wide open making it harder to create a vacuum against that much air.
3. The vacuum at the throttle plate drives the FPR with or without the check valve, although a failing check valve would make it harder for the regulator to run well at wide open throttle
4. There are other things in the car that needs vacuum to operate correctly, the bypass exhaust valve is one such animal. For that reason, there is a vacuum reservoir (the tomato can) and associated lines to the right of the engine compartment providing this function.
5. The two check valves (one on each bank) are there to help the reservoir system to build and maintain vacuum to drive the bypass valve.

IF that check valve has failed, it would be difficult to maintain a high level of vacuum in the reservoir at high throttle.

SO, when you smash the throttle, your engine creates the least amount of vacuum. Added to that the failing check valve and the reservoir has the least amount of vacuum available to it. The computer instructs the bypass valve to open (because you smashed the throttle) and it draws more vacuum from the whole thing which takes vacuum away from the fuel pressure regulator. That messes up the fuel delivery of that bank at wide open throttle.

Does that sound like what happens when you imitate Mario Andretti?

 

Correct. Every throttle body feeds that vacuum line at the base of the throttle body via hidden holes. The vacuum lines suck on the FPRs and vacuum tank.

Glad you found the problem.

 

There should be no check valve between the TB-s (intake manifold) and the FPR. The FPR needs to see the changing vacuum in the intake manifold so that it can adjust the fuel pressure accordingly: higher vacuum - lower pressure; lower vacuum - higher pressure. In this way, the FPR keeps the fuel pressure constant in relation to the manifold pressure which ensures a constant flow through the injectors. Without this compensation, the injector flow would, at a given fuel pressure, be higher at higher intake vacuum and lower at lower vacuum.

 

I think what Mitch meant was that the FPS will work with or without a check valve in the vacuum line between the throttle body and the vacuum canister.

 

This is a clue, if only I know what it means ... yet.

 

I know what it means.

Excess gasoline was inside a cylinder when the "wasted spark" was introduced into the cylinder. You have over injection of fuel possibly from a leaky injector, or a bad fuel regulator.

 

Is there a reason why injectors are so expensive? U$684 plus tax and shipping... each?

https://www.eurospares.co.uk/parts/ferrari/355-52-motronic/engine/throttle-holders-and-controls-41063

Grant, do you have standard FPRs and injectors? Didn't you have the gold kit fitted to your injectors?