225 Optimax Pro XS fuel pumps

[ctucker]

Has anybody ever ran across a high pressure fuel or booster pump that draws high amperage but still works?
I am trying to diagnose a excessive voltage drop that occurs when running. Alternator cannot keep up with the electrical load that the motor is pulling.

2005 - 225 Optimax Pro XS - s#1B150400

[swolt45]

YES!!! I HAVE!!! I'm not saying this is your problem but the connectors in the wiring harness were kind of corroded and one of the pins had pulled out a bit creating resistance. Let your motor run for a bit and feel that plug. Also could be a bad connection inside the vst. Zip tie the plugs inside the vst too. My plug was so hot that you couldn't touch it

[EuropeanAM]

+1

There are numerous other potential causes, including poor (or no) charging occurring, bad or inadequate battery, etc.

Suggested steps to start (after checking for a hot connector as described above):

-Note capacity PRINTED on battery ______________

-LOAD Test Battery. Actual test rating: ______________

-Voltage at battery BEFORE Starting: _______________

-Voltage at battery 5 minutes after starting: ____________

-Voltage at LARGE RED output lead on Alternator: ___________

[ctucker]

Don,
Here are the answers based on what I have been experiencing. Note - This is with a brand new OEM alternator

Capacity of the battery - 1150 CCA - Diehard Platinum PM1
Load test - tested OK - had it done at Interstate so that Sears could not BS me
Voltage at battery before starting – 12.0 after fishing half a day
Voltage at battery 5 minutes after starting – 13.2 at idle
Voltage at Large red lead -13.2 at idle

Here is what happens starting with all of the readings above - I get the boat on plane and start down the lake. Running at 1/2 trim and do not trim up or down. As the RPMs increase the voltage decreases, until it is down to 11.4 volts and the alarm sounds. I can reduce RPMs and the voltage comes backup until the alarm stops. Increase the RPMs again and the voltage will drop again. Shutdown to idle and the voltage goes back up to over 13 volts.

What I have done so far:
1. Replaced the alternator
2. Cleaned every ground I could find
3. Replaced the ignition coils and drivers
4. Replaced the spark plugs.
5. Ohmed out the fuseable link (it had continuity but I ordered another one in case the wire is corroded internally)
6. I am replacing the battery cables as soon as the new ones arrive
7. I am replacing the alternator harness as soon as it arrives

The reason I asked about the fuel pumps is because the problem really appears to be related to a high power draw from something in the outboard. The voltage drops as the RPMs increase. Also I can see burn marks at the VSR fuse where it has blown at some time in the past before I owned it (however it has never blown on me). I have discussed it with two different Mercury master certified mechanics but both are stumped. They both just keep saying that I must have a bad alternator.

[Savage]

Aftermarket alternator, or Genuine Mercury Marine?

[ctucker]

Genuine OEM

[ctucker]

Would it be a good idea to go ahead and replace the main power relay while I am at it?

[EuropeanAM]

I doubt the problem is there.

Look for signs of oil or water leakage inside the cowling (often leaves behind telltale hard-water spots).

If none are noted- shove a rag firmly up under the alternator, and go run it for 10 minutes down the river.

Pull the rag and see if it is completely dry...

[ctucker]

Thanks Don, I will try that Saturday