Converted from manual to power brakes, where to put the booster vacuum line?

[demonpixel]

Ever since I had the shop convert my 72 Formula from manual to power brakes, my car stutters slightly sometimes on startup. It didn't do that before when it was a manual brakes car.

I'm thinking it might have something to do with vacuum. Because...

My throttle body EFI system comes with 3 vacuum ports. The one in the back is a larger port and the instructions say it's "used for power brakes and/or PCV."



The 2 ports in the front are 3/16 ports and are used for vacuum accessories and the MAP sensor for the EFI system.

There is 1 port on my Edelbrock intake manifold, and that goes to the MAP sensor for the MSD ignition system.

When I upgraded to power brakes, the shop that did the installation teed off the line that went between the intake manifold and the MAP sensor for the MSD ignition system. So from the intake manifold, it goes to the brake booster, AND the MAP sensor for the MSD system because of the tee.

I don't have access to the car at the moment since I'm in the middle of moving but I wanted to ask - would this, in anyone's opinion, be a cause for a MAP sensor to not read as much vacuum as it did before when it was a straight connection without the tee? Would it make any difference at all?

Should I tee it from the rear port since it specifically says that port is for power brakes AND/OR PCV (right now that line is part of my PCV system)?

Thanks again for any help guys,
Zig

[67 455 Bird ragtop]

My guess is yes. Whay might be happening is your booster is trying to recharge itself at the same time the MAP sensor is trying to start the car. So the MAP reads a lower vacuum than it should until the motor is running. Another problem that could also occur is when you use your brakes the MAP will loose some vacuum and cause fuel mixture issues. But I'm no EFI expert. This just seems logical to me.

If there is a port specified for powerr brakes your installer should have used that instead of teeing off a vacuum source used by the computer to control your EFI. Personally for an installer to disregard ther mfg instructions and select his own vacuum source for your brakes borders on incompetance. Or laziness. But that's just MHO. My suggestion is whe you get the car back connect your booster to the specified port.

[demonpixel]

Thank you for taking the time to read about my issue. I'll connect it according to the instructions tomorrow - what you said makes sense to me also.

[demonpixel]

Ok,I made the MSD map sensor directly connect to the intake manifold, and it's much better now.....but...

I notice a light shudder when lightly accelerating around 40-55 mph. If I keep the accelerator pedal steady at part throttle, cruising at 55mph, it sounds like dud-dud-dud-dud-dud-dud-dud-dud-dud-dud-dud-dud. lol It's hard to explain. When I take my foot off of it and decel, it goes away, and if I "push" through it, it goes away.

I'll stick my laptop to it and try to see what AFR I've got. Maybe I'm running too rich if it's shuddering a little like that.