Usually when a 5th port injection is used you pull the signal for rpm from the injector. On the ecoboost this is not possible because of a strange firing sequence Ford has in the ECU. It doesn't keep a solid RPM so the coils have to be used for the RPM signal. The problem with that is when you let off the throttle the coils still send a signal and the controller doesn't stop instantly. The injector signal would instantly cut out. So for a second the fuel is still dumping. Let off the throttle and the car goes into vacuum. Fuel is not going to flow up through the manifold and be ingested. It's really simple actually. I spent a lot of time with Mark from split second working on the issue and it's fixed. I had to build a separate circuit to dissipate the signal however I will not share how its done. It's been installed on all the aux systems I've built.
Ok... It's cool that you've found a Power Puff Girls band-aid, but you didn't answer any of the questions I have... You just told how to you developed a "circuit" to prevent pooling. To be honest, now that I'm a little more awake, the question remains the same, even with whatever capacitor/resistor circuit you've concocted.
In the event of a backfire, what is preventing the plastic manifold from popping?
Let's look a what a backfire is: Briefly, it's when combustion takes place in the intake, caused by the AFR being too lean. Also, badly tuned timing.
So [MENTION=3244]STeve[/MENTION]... Consider what a backfire is and that it typically happens on acceleration. In the event of a one, if there is MORE fuel than usual at the intake (this includes port injection on DI) what is preventing the intake manifold from exploding?
Also, one more thing to consider: GDI engines tend to have plastic intake manifolds. MPFI are cast, or metal of some sort. I wonder why.