If they made a troubleshooting PCM? It could have a lot more horsepower than the factory PCMs -- which are limited by cost. Here are some of the things that I think might be possible

1. Robust connection to a laptop to display engine parameters
-- Now you could see how all of the sensors are acting
2. Modification of the rules for runnung the engine
-- substutute generic numbers for a suspect sensor
-- force the engine to operate in a certain manner under specified
conditions. Suppose you think that it's running too lean at some
operating range -- you could change that part of the system
operation to see if you were right.
3. Provide a 'known good' PCM -- goes without saying that this unit would be
'hardened', so that if you put it in an engine with defective electricals, it
would survive
4. Be adapatable to a large number of vehicles. This probably wouldn't be a cheap unit, so you'd want it to be compatible with a lot of vehicles.

I don't know if I'm explaining this well, but it seems to me that you could do a lot of good troubleshooting with something like this. Normal obdii troubleshooting depends on a PCM that is pretty limited from a troubleshooting perspective -- it's designed to run the vehicle -- not to
really isolate problem areas. With a gimmick like this, you could modify the MAF input if you suspected a leak. You could disable the O2 sensor input to see if a bad O2 sensor was hosing your system. The list goes on. I don't know enough about the seemingly problematic egr system, but I'd bet that you could find out things about that as well.

Just a thought from someone far too lazy to pursue the idea,

ford2go

 

The already have these that do most of what you want, and they are expensive. Snap On's starts at $3,500, and you add on from there. There are other mfgr's also, and also very expensive. Ford's is something like 5 grand if you can get one. jd