blown3rdgen

My friend just got his car back together, including dyno tune. It is a fully built 388 with D1SC @ 12psi. He had been having some problem starting it-etc, so we were looking around and I noticed the vacuum line going from the throttle body to the vacuum canister was not hook up (like a 5/16" line). We plugged it in, and seems to be fixed.

Vacuum unplugged = 15" @ idle
vacuum plugged = 20" @ idle

We are unsure if the dyno tune was with it plugged in and maybe blew out under boost. If it was tuned with it unplugged, and is now plugged what will it effect. How will this effect idle/cruise air fuel ratio? Fuel pressure? Also would he gain any boost?

This is what I think- I would think he would make more boost without the leak, minimal I'm sure. I also am afraid the added vacuum could cause him to lean out a bit at idle/cruise, but should not effect wot air fuel. Is this correct?

Thanks
Matt

1racerdude

Vacuum leak will make it run lean across the board on motor. Under boost it would probably richen it b'cause it's loosing boost and if ya are using an FMU it will change the setting.
Hope ya got check valves on everything.

blown3rdgen

I'm thinking leaner as well. However the car is not a mass air car (which would definitely be a problem) so maybe the map and O2 could help correct it some. No FMU all controlled by FAST stand alone system.

Either way, I know the only way to be 100% is to get it back on the dyno

1racerdude

On the blown Fords I have built I have put a check valve in the PCV line to keep boost out of the pan and blowing oil out everywhere. You could do the same and make it run better and cleaner.
Yea dyno it again and see.