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$).
If you haven't got the 108-109-111-113 manual I strongly suggest you get one (try the parts shop first, then try 1-800-for-merc, lastly try ebay).
Send me an email and I'll reply with a zipped file that has all the relevant manual pages on the system from several sources.
PS. It doesn't hurt to have the box that Chris mentioned, he should know, he has mine.
But a mulitmeter and some patience can do the job. BTW, a working ECU just sold on ebay yesterday for 50$. A non-working one for 14$.