'98 Mercruiser 5.7 EFI Electrical Puzzle

[84LiIrish]

I appreciate any advice on how to diagnose and fix this issue.

My boat is a '98 Sea Ray 290 Sundancer with twin 5.7 EFIs with about 600 hours. This issue popped up during the return leg of a quick trip to a dock & dine.

After cruising for about 15 minutes, the alarm on the port engine began to go off intermittently. After a minute or so, it came on steady. At this point, the voltage guage for the port engine dropped to less than 10 volts and became unsteady. We slowed to idle within a few seconds of the alarm going off. The alarm stopped the steady warning but you could hear it clicking (like it wanted to alarm again but couldn't). The engine did not loose power or run rough. IT felt perfectly normal.

We shut down the port engine, then started back up after a couple of minutes. The engine ran normal for 2-3 minutes and then the alarm started again and the guage showed low voltage again. We left the port engine off and cruised home on the starboard.

Back at the slip I checked the voltages across both guages. The starboard engine showed 16V, the port was just below 14.

I'm at a loss for possible causes: coile? voltage regulator? something else?

Any ideas are much appreciated.

 

[wingless]

Use a good volt meter, not the dash gauges and check the alternator output w/ the engine running.

It should be about 14 VDC.

Back at the slip after plugging into the charger?

Both engines sound bad. At 16 VDC the batteries are being damaged, unless part of a smart charge cycle.

At 10 VDC w/ the engines running the alternator is hosed. It may be an internal replaceable regulator.

The alternator on my engine doesn't have a replaceable regulator and had to be swapped as a unit.

 

[Stromeister]

Have you checked the water level in your batteries?

 

[Mike-n-Jolie]

Use a good volt meter, not the dash gauges and check the alternator output w/ the engine running.

It should be about 14 VDC.

Back at the slip after plugging into the charger?

Both engines sound bad. At 16 VDC the batteries are being damaged, unless part of a smart charge cycle.

At 10 VDC w/ the engines running the alternator is hosed. It may be an internal replaceable regulator.

The alternator on my engine doesn't have a replaceable regulator and had to be swapped as a unit.

I concur. Although,it could be a voltage drop somewhere(loose/corroded ground,power distribution etc.) So yeah,check the charging system(preferably while the problem is happening) and if it is ok-start looking elsewhere. Good luck with that.

 

[84LiIrish]

Thanks for the feedback. The batteries are OK, so far. I'm pretty sure they are doing OK because I've had no problem starting both engines repeatedly.

I will check voltage with a voltmeter across the alternators and across the guages. Someone on another board also suggested that I clean the main harness connection.

I'll let you know what I find in a couple of hours.

 

[84LiIrish]

On further inspection, I found that the connection to the positive side of the alternator was completely loose. It looks like there may have been some arching at some point. I cleaned up and tightened both terminals. The boat started fine, the voltmeter needle was steady, but low 10v. No alarm. I'm hoping that replacing the regulator will fix this.

The starboard engine is still a mystery. Voltage reads 15-16. Perhaps a new regulator here also.

Thanks to all for your help.