Need help troubleshooting charging issues

[thormx11]

1995 Mercruiser 5.7l engine with serpentine belt setup

So, after replacing the engine in my boat (which took about 5 years) I am finally getting it running and breaking the new engine in. Previous to the block cracking, everything worked/functioned as it should have on the engine. Now, the solid alarm won't stop buzzing. I believe I have tracked it down to charging ( Engine & drive oils are full, and getting about 40 psi oil pressure).

The boat has 2 batteries, 1 is brand new, the other is a good used one I have in there for now until I pick up another battery. With the engine off, I am getting about 12.2 volts at the back of the alternator, but the gauge is only showing about 10-10.5 volts. With the engine running I am getting about 14.5 volts out of the alternator, but the gauge still only shows about 11 volts at best. If I unplug the 2 wire pigtail from the alternator with the engine running the gauge goes up a tad, maybe to 12 volts, but the alarm still stays on (I forgot to check voltage coming out of the alternator at this time though) With the alternator unplugged & the battery cable disconnected from the alternator, it is putting out 16.0 volts running.

I noticed, while running, if I turn on any accessories (bilge, blower, etc) the gauge drops down another volt or so.

Before hooking the alarm up, I ran the engine for about 2.5 hours on the water hose with only 1 battery in the boat to break the engine in. Everything seemed to be good, oil pressure was good, temp stayed good, voltage gauge was about where it reads now with 2 batterys, but I did not check actual voltage from the alternator then. I figured the voltage was low because it only had 1 battery, but now that I think about it, shouldn't the alternator put out the same voltage once the engine is running?

 

[Bondo]

Ayuh,..... Is this motor carbed, Efi, or Mpi,..??

If carbed, the alarm is hooked to 3 sensors,....
Low oil pressure,....
High water temp,....
Or low drive oil in the bottle,.....

Disconnect each 1,... 1 at a time til the alarm goes off,... That's the bad sensor,....

No voltage alarms,..... sounds like the gauge is pooched,....

 

[Bt Doctur]

am getting about 14.5 volts out of the alternator

Thats what your supposed to be getting, if the dash is different suspect bad grounds

With the alternator unplugged & the battery cable disconnected from the alternator, it is putting out 16.0 volts running.

You never run a alt with the battery disconnected, you will fry every piece of electronuics from over voltage

I noticed, while running, if I turn on any accessories (bilge, blower, etc) the gauge drops down another volt or so.

You have a bad ground someplace

 

[thormx11]

Thanks for the tips. It is a carbed engine. I will double check all my grounds. Hopefully I didn't fry anything!

I will try to check the sensors. I know the sensor for the drive oil, but the oil pressure & coolant temp I am not 100% of. There is 2 sensors on the thermostat housing (1 is a single single wiring bolted to the senor, and the other has a 2 wire pigtail that plugs in that I believe to be the coolant temp sensor.) Then there is also a sensor down in front of the started going into the block that I believe is also some type of coolant sensor.

If I remember right, there was a sensor going into the block in the rear top of the engine, by the distributor. Not sure if this is oil or what?

Sorry for the vague explanations, I know it is probably hard to figure out what I am talking about without any pics, but my boat is stored in a building away from my house.

 

[Scott Danforth]

yes that is oil at the top of the block. if in doubt, follow the color codes [h=2]American Boat and Yacht Council Standards[/h]

Black	Ground	Negative / Neutral Main Return
Blue-Stripe	Tilt up and or trim out	Tilt and or trim circuits
Brown	Alternator Charge Light	Generator Terminal or Alternator Auxiliary Terminal to Regulator
Generator Armature	Generator Armature to Regulator
Pumps	Circuit Breaker or Switch to Pumps
Brown w/Yellow	Bilge Blowers	Circuit Breaker or Switch to Blower
Dark Blue	Cabin & Instrument	Circuit Breaker or Switch to Lights
Green or Green w/Yellow Stripe	Bonding System	Grounding Wires (if insulated)
Green Stripe	Tilt down and/or trim in	Tilt and or trim circuits
Grey	Navigation Lights	Circuit Breaker or Switch to Lights
Tachometer	Tachometer Sender to Gauge
Lt. Blue	Oil Pressure	Oil Pressure Sender to Gauge
Orange	Accessory Feed	Ammeter to Alternator or Generator
Common Feed	Distribution Panel to Accessory Switch
Feed	Accessory Circuit Breakers or Switches
Pink	Fuel Gauge	Fuel Gauge Sender to Gauge
Purple	Ignition	Ignition Switch to Coil & Electrical Instrument
Instrument Feed	Distribution Panel Electrical Instruments
Red	Instrument Feed	Distribution Panel to Electrical Instruments
Power Feeds	Positive Main Power (particularly un-fused)
Tan	Water temperature	Water temperature sender to gauge
Yellow	Generator Field	Generator to Regulator Field Terminal
Ground	Negative / Neutral Main Return
Yellow w/Red	Starting Circuit	Starting Switch to Solenoid

COLOR ITEM USE

 

[alldodge]

other has a 2 wire pigtail

This is your temp switch

 

[thormx11]

I probably won't be able to work on the boat any until saturday, I'll report back with what I can find. Thanks for the info so far

 

[thormx11]

So I got the boat out this morning and brought it to the house to try and track the alarm problem down. I disconnected all 3 sensors as mentioned and the alarm would still sound each time. I looked up under the dash and noticed the purple wire coming out of the alarm was hooked to the purple wires (there' 2) on the ignition switch. The other tan wire coming from the alarm is grounded yo the carb on the engine. I am thinking the purple wires on the ignition switch are a constant power wire and the alarm wire does not belong there.

should the purple wire on the alarm be hooked to somewhere else?

 

[Scott Danforth]

purple wire is ignition.

 

[thormx11]

After doing some googling and reading in my 1998+ shop manual (I know, a little newer but still close) I found the purple ignition wiring is correct. But someone has ran a new tan wire from the alarm all the way to the engine, bypassing the factory wiring harness and connector on engine. I am going to try to tie the tan wire into the tan/blue wire going to the drive oil bottle sensor.

 

[alldodge]

I am going to try to tie the tan wire into the tan/blue wire going to the drive oil bottle sensor.

That's a good step

 

[thormx11]

Thanks everyone for the info & tips.

Alarm seems to be working correctly now. It sounds when the key is on/engine off and stops shortly after engine fires up.

Still have to figure out the charging gauge issue though, but I am not as worried about it. I know the alternator is charging correctly.

Only a few more little bugs to work out and itll be ready for the lake!