Stalling, Alarm sounding every 60 seconds

[sunblind]

I have a 2001 Deck boat powered by a Fuel injected 5.0L Mercruiser and Alpha drive. Two weekends ago we were about 2 hours into a lot of tubing and skiing when it lost power. It never quit running but would not accelerate over 900 rpm. When i asked it for more power it would pop through the intake so i figured it was running lean. On the 2 hour trip back to harbor at 900 rpm, an alarm would sound every 60 seconds and beep two times. I got it back to my shop and found only 20 lbs of fuel pressure so replaced the fuel pump, fuel filter and water/fuel seperator. The next trip out we experienced the same exact problems after about a 2 hour hard use run. Hoping someone can steer me in the right direction and also tell me what kind of scan tool i need to properly diagnose this type of system. TIA for any help you can give me

 

[alldodge]

What is the motor serial number?

 

[sunblind]

Engine Serial # 1A614666

 

[alldodge]

Thanks, you have a motor with CAT's and its had signaled guardian strategy
For 90% power reduction I would look at Engine Coolant Temp (ECT) overheat or Sea water pressure low.

Being a CAT motor you really need to have the motor scanned for codes. This can be done by a dealer or by buying the Rinda Techmate pro or Diacom software

https://www.rinda.com/marine/marinemenu.htm

 

[sunblind]

Finally got it to reproduce the problem today. Bought a scanner. It set a code for "sea pump pressure low".

 

[alldodge]

That is the number one failure of the Merc motors. They fail often and there is no pressure issue. Dang things are expensive for what they are

Could test with a mechanical gauge (0-30 psi) Tee'd in same location