ProDiag and 200TQ questions

I have a few questions that hopefully, someone here can answer. A little while back, I posted about some hesitation problems I was having in my 91
200TQ. Got quite a few responses about what to check and all that. Decided that what I was going to do is put it up for the winter and try to get it done and ready by the time summer rolls around again. To do the checks, my Bentley books say to use the VAG 1551. I don't have that, and really can't justify the cost. So, I've been looking at the ProDiag through SJM Autotechnik. I don't have a lap top, and would need around a 50' wire to get to my desktop, so the Palm Pilot option is what works best for me.
I know with my car the ProDiag can only communicate with the engine control unit, and the airbag control unit. I know the problem with the car is in the fuel delivery system. The question is, by conecting to the engine control unit, will the ProDiag be able to figure out what the problem in the fuel system is? Or will it just tell me that there is a problem with the engine receiving fuel?
TIA and Enjoy Bill
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