When the 7730 ECM in a 91-92 F-body sees positive manifold pressure (aka. boost) how does it react?

Does it see zero vacuum and therefore assume it is at WOT and apply timing/fuel accordingly?

or

Does it see a hi-MAP pressure reading (ie. the far end of the 5v scale), throw a code and then go into limp mode to protect itself?

It seems that the popular answer in this regard is to throw fuel at the motor at a 8:1, 10:1 or 12:1 ratio via a fuel management unit (FMU) and "increase" the flow of the injectors to make up the fueling differences in boosted situations. As such, I am getting the impression that the ECM just locks out it's VE table, timing and fueling when the MAP (load) is pushed to it's limit.

Any insight would be greatly appreciated.

 

The ECM doesn't care. It's the code / tune and MAP sensor that does. You're running an 8d code and a 1bar MAP sensor which does not take into consideration anything above 100kpa. That is why FMU's are a popular band aid. I'm going to say not the best but certainly useable and probably reliable if you do not want the real fix to putting forced induction on a car using a 730ECM. The "real" solution I'd say is run a code / tune that does allow for boost, such as $59 code. (reference www.code59.org). That is what a few of us run on our cars and still keep the 730ECM. There are a few other things needed besides the code, like another MAP sensor. You need a 3bar for the $59 to work.

 

Good to know.

Essentially what one could do prior to taking the (agreed) proper route is to get a basic chip burned with their preferred injector size and work with the hi-rpm/hi-load/spark-advance table as a fixed figure and tune to that with boost and a rising rate FPR/FMU. One could possibly tune out KR with the base timing at the distributor and/or a boost referenced timing retard box; and of course octane.

In the Turbo Buick World it is not much different than this, as in a lot of cases the MAF signal is maxed out over stock boost levels and the ECM is usually rigged to continue to function and not crap all over itself. In fact in stock configuration the LC2 doesn't even know it is under boost (no MAP input), just air flow figures (MAF).

Yes, I have spent a lot of time reading the archives of Code59 and it is a great piece of work no doubt. However, on the cheap and easy it is nice to know the SD TPI system won't have kittens when it sees positive pressure in the manifold.

 

One of my friends runs a SD TPI setup on his 305 and D1SC. I saw his dyno video where he put down 385rwhp, so you're right, the SD TPI setup doesn't have kittens.