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1997 Honda BF90A Voltage Gauge Fluctuating

moctod

Member
1997 Honda BF90A. Voltmeter and Tachometer acting strange.
At idle, approximately 900 RPM, boat voltmeter and tachometer appear to give accurate readings. As RPM is increased boat voltmeter voltage drops and tachometer fluctuates. Thought voltmeter was bad so connected Fluke multimeter to boat voltmeter terminals. Fluke meter confirmed meter was relatively accurate. The following readings were taken at various RPM.
RPM
Boat Voltmeter (approximations)
Fluke on Boat Meter Terminals
Fluke on Battery Terminals
900
13.5 vdc
12.49 to 13.38 vdc
12.84 vdc
1000
4.5 to 12.5 vdc
4.9 to 11.77 vdc
12.82 vdc
1500
4.5 to 5.5 to 10 vdc
2.6 to 12.95 vdc
12.77 vdc
2000
4.5 to 10.5 vdc
6.12 to 10.5 vdc
12.75 vdc
3000
4.5 to 5.5 vdc
7.2 to 7.97 vdc
12.8 vdc
Sometimes when boat voltmeter is low in 5 vdc range hitting tilt switch will cause voltage to return to approx. 13 vdc. Tachometer does not fluctuate as much or as rapidly as boat voltmeter. Motor will run with battery disconnected but will sputter at low RPM. Tilt will not operate when boat voltmeter is reading in 5 vdc range.
Any ideas?
 
Sounds like a bad ground or a bad 12v lead somewhere.

The most common place is corrosion in the 14 pin connector on the engine, but there could also be an issue with one of the connectors at the helm end of the wiring harness.

The odd thing...I did not think that this motor would run without a battery. The ECU uses the battery voltage to multiply it to an appropriate voltage for the coils.

Run a jumper wire from the negative of the battery to a gound post on one of the gauges and see if that clears it up. If not....then run a jumper from the positive terminal on the battery to one of the positive (ignition) posts on the back of one of the gauges. Retest for proper operation.

If either of these clear up the problem, then you will know if you are looking for a ground problem or the positive voltage problem.

Of course...make sure your battery terminals are shiny clean and wrench tight.

Mike

PS. Many more questions to follow, if the two tests do not work out.
 
Thanks Hondadude! Got side tracked for a while on the honey do list. It was a bad ground. I've rebuilt the console twice and am currently using Mercury controls with a Honda harness. You can imagine what the wiring looks like or maybe you can't. Couldn't locate the bad connection it so I ran a new ground wire. Now it works like it has good sense. The engine (1997 BF90, carburetors not fuel injection) will run with the battery disconnected. I let it run for a few minutes and it ran fine. Didn't want to press my luck so I didn't run it for a long time without the battery. Thanks again for the help.
 
Glad you solved it....and yes, I can imagine what the wiring looks like.

Just a note for the future....if you have issues with shifting...that is it will go into reverse by not forward or vice versa or will not go back to neutral all the time, you may have to step up and change the shifter to a Honda shifter. The 90's of that vintage did use Mercury shifters....maybe because it used a Mercury gearcase. There is a subtle difference in the throw of the Mercury shifter compared to the Honda.

Mike
 
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Hey Mike, spoke too soon, took boat out today and everything looked good... for a while. Cruising at about 3500 RPM and volt meter and tach start bouncing again. Volt meter goes to 0 and tach fluctuating between 3000 and 4000 RPM. Slowed down to 1500 RPM everything goes back to normal. Speed up and after a minute or two voltmeter and tach start fluctuating. Weird thing happened.... when running at about 3500 RPMand voltmeter was at 0 I used the tilt and engine died when tilt switch was used, only while tilt switch was depressed, engine came right back to life when tilt switch was off. Tried this a couple of times and same thing. This only happened when voltmeter was at 0 volts. When voltmeter was fluctuating between10 and 13 volts tilt was very slow. Other strange thing is voltmeter reads about 14 volts at idle and decreases to about 12.5 volts as engine speed increases.
Had been having trouble with the voltmeter for a while, I'd sometimes have to thump it to getit to start working. Right now every thing seems to work fine while at low RPM, trouble starts as RPM is increased. I know the fuel gauge sending unit is bad but it is still connected. Doesn't seem likely but can a bad voltmeter or fuel sending unit be causing this problem?
 
Small Miracles!
Started going through the wiring harnesses and connectors looking for either a bad connection or a shorted wire. If you've ever done this you know its a tedious and frustrating process. After checking the ground connection on motor I just happened to pull the rubber boot off of the positive cable connection to starter solenoid. The threaded terminal post uses a hex nut with an attached lock washer. The hex nut, attached lock washer and cable ring connectors were loose, very loose and the lock washer was completely flat. I installed an additional lock washer, some conductive grease and tightened the nut. Started the motor and immediately noticed the voltage meter was up about 13.5 volts. Revved the motor and the voltage climbed to almost 14 volts. Took it out for a test run and everything worked fine.

I assume that at low RPM the motor was not vibrating enough to create a bad connection.At higher RPM's the vibration created a bad connection that caused the voltmeter to go to 0 volts. When the tilt switch was used the voltage drop created by the hydraulic tilt motor caused the ICM to shut the motor down. Any other ideas?
 
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Good troubleshooting. It is always an easy......once you find the problem.

Your explanation sounds consistent with your problem.

Mike
 
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