FiTech EFI system
If the mechanical is locked either on a regular or a lean burn distributor, can vacuum advance still be used?
NO. Zero advance of any kind. needs to be 100% locked.
I"m seeing some confusion on if/why a distributor needs locked, and if/why any type of external control box (mopar or non) needs to be present.
let me clarify.
All the fitech units (with the exception of the incoming go-street 400 system) Have the ability to FULLY control timing. SO..if you utilize the fitech to control your timing... you can eliminate any form of external control/ignition box, and furthermore the ballast resistor.
This Means: your timing is now completely controlled by the unit. NO mopar box, no MSD box, nothing more than a fully locked distributor...and the fitech electronically advancing and retarding timing.
The distributor needs fully locked so the fitech knows where the rotor is physically (mechanically) at. This is so it can throw big amounts of timing at the engine while at low load, and cruise (sounds similar to a vac advance doesn't it??) and also control timing for acceleration and load (exactly like a mechanical advance would do :) ) it does all this electronically, on its own.
NOW..can the unit run in "fuel only" mode, where another means of ignition control is used?
YES....now having a mopar..not sure why anyone eyeing this unit wouldn't jump at the opportunity to toss the ballast resistor in the trash...BUT if you just shelled out some cash for a fancy MSD box, or DUI distributor, and you like the fact that timing is mechanically and/or vac controlled...then so be it. GM guys COMMONLY leave their HEI distributors, and run the fitech in fuel only....but again I've never had luck with mopar ignition, so it's extremely attractive (to me) to eliminate the factory box, lock the distributor, and let the fitech do it's EFI thing!
Lastly, As i am politely reminded below (thanks!), you CAN retain and run an MSD box for things like multi-spark, while wiring the fitech for the timing control, but it's not at all required. I'm going to attach the instructions in this edit, which will also help with explanation. Not too many guys go this route, but the option is out there. I didn't cite it originally as it's the least common of the three, and it's a little double redundant. especially if you don't already have a box in the car.
hope this helps you guys...again please message me for contact info if you need further clarification.