1998 Merc 115 Humminbird Interference

[RayJackson]

I have a 1998 Mercury 115 2+2 Serial # OG738893 on a 1998 Nitro that I've had since new. At some point over the years, the humminbird depth finder, also original, began losing depth reading while traveling at speed. The depth reading would NOT return until the outboard was powered off. I routed a dedicated power wire to my isolated trolling motor battery with no change. I lived with it until the transducer wire gave up the ghost.

Recently, I installed a new Humminbird PiranhaMAX 4 DI and am experiencing similar issues. The unit will stop displaying depth, switch to the max depth range, and continue to draw the bottom when at speed in deeper water. It seems to operate normally in shallower water and when slowing back down to idle speed. This unit does NOT require me to power the outboard down for it to return to normal functionality. Now that I described it, it sounds more like poor transducer placement, but it's located 12" from the rear and 2" off center of the pad, so I don't think that's the problem, especially given the issues I had with the original depth finder.


Any troubleshooting advice you can give will be greatly appreciated.


Thanks,
Ray.

[JOE54]

would be a very good topic in the HUMMINGBIRD forum , when you connected it to trolling mtr batt you eliminated mtr as source of problem , good luck JOE

[RayJackson]

JOE,

Thanks for taking time to respond. It just seems odd that I've experienced problems with 2 different units that were 20+ years different. The only thing that really ties it to the outboard is that the original depth finder would return to normal operation as soon as, and only when, the outboard was powered down. Any chance of interference through the transducer cable? I have not tried rerouting it away from the main wiring harness.

[EuropeanAM]

Transducer needs to be at least 12" off center of engine (not 2" as stated in first post).

It's not uncommon to lose sonar at higher speeds, as by the time the signal bounces back to the surface your boat is no longer there. A tiny bit of improvement can be found in "tweaking" the position, but that also skews the readings (and reduces accuracy at lower speeds as well).

More help can be found in the Humminbird Forum (as Joe suggested).

[RayJackson]

EuropeanAM,

Thank you for your response as well. I should have noted that both transducers were mounted inside the hull.

On a potentially related note, is 15.58 volts at the battery at idle too high? I found some yellow wires beginning to melt together coming out of the voltage regulator which led me to do a little testing. I'm reading 12.77 volts 30 minutes after powering off the engine.

[JOE54]

yes thats too high shouldnt exceed 14.5 underway , you have a regulator problem sir

[RayJackson]

JOE,
Thanks again for your response. I'm assuming it's only the regulator that needs to be replaced. Is there a recommended replacement to purchase? I'm seeing options from $25-200

[JOE54]

absolutely OEM only replacement

[EuropeanAM]

+1... OEM Mercury/Quicksilver ONLY. Also need to replace any of the bullet connectors that are discolored, browned, blackened or Burnt with OEM connectors.

[RayJackson]

I'm back and was hoping to report success. I replaced the regulator with an OEM. First trip to the lake everything worked perfectly for the first time in years. I thought the problem was fixed. Second trip, my problem was back. I just ran a test in the driveway and am experiencing 15+ volts again at idle at the battery. Here's something even more odd. With the motor running, I'm seeing .3 - .4 volts on my meter without the leads being attached to anything. When I turn the motor off, it drops to 0 as expected. When I crank it back up, it goes to .3-.4 volts just sitting there not attached to anything. Any advise you can give would be appreciated.

[EuropeanAM]

Clean and properly connect battery cables at BOTH ends (Stainless NUTS or LOCKNUTS, do NOT use wing nuts).

Engine cables should be installed first, remaining lugs largest to smallest.

Make sure your battery is a traditional WET CELL cranking battery (ie: caps can be removed and electrolyte level adjusted).

Verify ALL bullet connectors (especially the ones on the YELLOW and BLACK wires) are in pristine condition, and properly connected (as suggested earlier, any browned, blackened, discolored or burnt connectors had to be replaced).

More than 90% of regulator failures can be traced to some type of poor connection at the battery (or regulator).

[RayJackson]

a little update... because of the ghost readings I was getting with my digital volt meter, I decided to check voltage with an old analog meter. Actual voltage was right at 14 at idle. After a little research, I ordered a set of resistor spark plugs for the motor and now the digital meter is reading 13.8 at idle. I'm hopeful that the interference I was seeing on my meter is the same thing that was causing my depth finder to act strangely. I'll update again after I've made a couple trips to the lake.

[RayJackson]

After 2 days on the lake, I believe it's safe to say the resistor spark plugs have solved the interference problem I was experiencing.

[EuropeanAM]

So precisely what spark plug are you now running?

[RayJackson]

Sorry for the late reply...
The sticker on the side plate of my motor says it requires a bp8hn10 and that's what I had been running in the past. I have replace it with a bpZ8hn10 which seems to have corrected the problems I was experiencing.

[EuropeanAM]