SD questions

[tmoss]

The EEC does know how much fuel should be being injected as it monitors the O2 sensors in closed loop operation. It will adjust injector pulse widths if needed to richen or lean depending on whether there is too much or too little fuel. In open loop (wide open throttle - WOT) the EEC ignores the O2 sensors and goes straight to the table look ups for fuel and spark. So, you can tune your fuel needs at WOT with the fuel pressure regulator and the EEC will tune A/F ratios back into spec when running part throttle normal driving conditions. This keeps fuel consumption at or close to stock.

[88workcar]

I have had a B, an E, and a wolverine 1087 in mine. E7s, ported E7s, big valve E7s, shaved E7s, Edelbrock performers, ported perfs, and now I am tring heavly ported perfs on a 342, ported cobra, cut and extended, and a X-cam reground by cam motion. I have had NOS on this car for 10 years. 70 - 100hp shot dry. And even a supercharger. All with 19lb injectors, (sep the super crger, 30s) It all worked. My car has seen many 11 sec slips, and whipped manny-a-ass. I an now tring to run 10s on the motor and a little more 10 on the spray. Do what you want and don't worry about the SD blues, its a myth, the people selling mass air are tring to get rich

I even made a box that fit on top of the stock lower intake and had 2 stock TBs on top of it linked together, that worked too.

[Unit 5302]

Originally Posted by tmoss

The EEC does know how much fuel should be being injected as it monitors the O2 sensors in closed loop operation. It will adjust injector pulse widths if needed to richen or lean depending on whether there is too much or too little fuel. In open loop (wide open throttle - WOT) the EEC ignores the O2 sensors and goes straight to the table look ups for fuel and spark. So, you can tune your fuel needs at WOT with the fuel pressure regulator and the EEC will tune A/F ratios back into spec when running part throttle normal driving conditions. This keeps fuel consumption at or close to stock.

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.

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. Also, the O2 sensors don't know how much fuel or air is being mixed in the engine so it can only read lean/rich fuel conditions, not actual air or fuel volumes.

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.

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

An analogy is the EEC is balancing its checkbook, but it only cares to get within $200. It thinks it knows how much money there is, but its balance doesn't match the balance on the bank statement (oxygen sensor). It looks at it's tables and counts deposits for $1000 (air intake) and it counts its withdrawls for $1000 (fuel injected). The problem is mom (the E303 camshaft) made a birthday present of $500 (air) into the account that it didn't know about.

[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.