[tmoss]

Originally Posted by Unit 5302

Well you have the theory right, but your deduction isn't really accurate.. It has absolutely no idea how much fuel it's injecting. It knows how much fuel it thinks it's injecting. Most of the time it also has an idea about how much more/less fuel it needs to inject. In addition, it knows how much air it thinks it's taking in which is where the problem arises. It's really clueless on both so if you modify only one variable it quickly throws a temper tantrum because nothing adds up.

You right about not knowing how much fuel it injects when it fires the injector, but it quickly knows in closed loop if it was too much or too little

Originally Posted by Unit 5302

The 02 sensors tell it how lean/rich the engine is running in closed loop, but since closed loop goes out the window about 3 seconds (unless you're an unlucky person with a Cobra) after you put the pedal down 75% or more, it doesn't even care what the O2 sensors are reading.

It goes into open loop immediately, there is no 3 second time delay. It monitors the TPS voltage and goes open loop at about 75% throttle.

Originally Posted by Unit 5302

The SD EEC has a finite table (which is much more flexible than MAF car tables) of injection data to use. If you go outside that table, the EEC assumes a sensor is malfunctioning so it either discards data or goes into limp mode, and this is when the drivability issues surface.

Are you aware of the Adpative Control feature of the EEC IV and how it uses KAM and under what circumstances it writes corrections to cam? When the EEC monitors out of specification air fuel ratios and it sees a "persistant" rich or lean condition it writes permament correction factors to Keep Alive Memory (KAM) for the table load cells that are out of spec which that are then used to change the permanent table "target" in that cell. This is how any EEC, even SD, can adapt to changes in air flow and fuel requirements. It's not an MAF function but it does adapt and does not throw a "fit" until you get about 20% on either side of the stock target ratio as it can't correct any further. The difference in the 87-93 and the 94-95 adaptive control features are the 87-93 does not use KAM in wide open throttle whereas the 94-95 EEC uses the last KAM written for WOT operation.

Originally Posted by Unit 5302

The idea is to keep the ratio of air and fuel coming into the engine close enough to stock so the EEC can compensate.

I have written articles on the EEC function that have been critiqued by more than a few people. They are posted at www.veryuseful.com/mustang/tech/engine and if I have an incorrect working knowledge of the EEC IV I'd be glad to listen to your critique. You'll also find articles by other authors on that site too, like Tom Cloud and Mike Wesley.