Can you handle a wrench or two on your own under the hood?
If so, you can pinpoint diagnose the whole system with 3 basic tools...
1. A multimeter.
2. A fuel pressure guage that can accurately read 20-40 psi.
3. a fuel line clamp (pep boys for about 8$).
If you haven't got the 108-109-111-113 manual I strongly suggest you get one (try the parts shop first, then try 1-800-for-merc, lastly try ebay).
Send me an email and I'll reply with a zipped file that has all the relevant manual pages on the system from several sources.
-CTH
PS. It doesn't hurt to have the box that Chris mentioned, he should know, he has mine.

But a mulitmeter and some patience can do the job. BTW, a working ECU just sold on ebay yesterday for 50$. A non-working one for 14$.