1998 mercury 200hp efi starts and dies

by Rock
(South Haven, MI, USA)

I have a 1998 200hp mercury efi. Owned it for five years. Two years ago I began to get an extended crank but it always started. Last year it started getting worse but it still always started, just a 30 second or more crank time. Today it seemed to give up the ghost. I do a pretty good job maintaining it but I'm no pro. List of service: new BU8H plugs twice a year (maintenance only very rarely foul a plug), new fuel filters (engine mounted with water separator and hull mounted) each year. Early this season I replaced the impeller and it started and ran fine when I tested for water flow. It has sat for a month since waiting for good weather when I'm not working. Now it won't start. After very extended cranking it will start for a moment and immediately die. Like I turned off the key. Throttle makes no difference. Sometimes when it starts it races up to almost 3,000 rpm's before it dies.

Fuel pressure: 40psi koeo, 38psi cranking, after long cranking begins to drop to 25 psi and holds there. I kill the key and it jumps back to 40psi. Seems to have good flow out of the pulsator.

Compression: CYL 1. 98 psi
CYL 2. 100 psi
CYL 3. 105 psi
CYL 4. 118 psi
CYL 5. 115 psi
CYL 6. 118 psi

Spark seems good: spark to all cylinders

Once the batteries get low it has no chance of firing.
When they ( 2 red tops and one yellow top ) are charged it will fire and die.

I think that's about the end of my list.

Please help!