Depth finder loses bottom with engine running?

[alvargo]

I have a Humminbird Wide 100 that loses bottom as soon as I start my engine (even idling in neutral). The Engine is a 1986 Johnson 70 HP. As soon as the engine shuts down the bottom displays correctly. The depth finder is wired directly to the battery and all connections are good. Wires are run opposite side of boat to other wiring. Any clue as to what to look for in the engine that could cause this problem? Plugs are new,wires look OK and the engine runs great?<br /><br />Transducer is transom mounted to fiberglass boat according to depth finder instructions. <br /><br />Thanks for any suggestions...

 

[Backlash]

Re: Depth finder loses bottom with engine running?

If you're not using resistor type spark plugs, that might be the problem. It sounds like you've done everything right in your installation of the unit.<br />Backlash

 

[alvargo]

Re: Depth finder loses bottom with engine running?

I'll double check to see if I indeed installed suppression type spark plugs when I get back to the boat on Monday. I may also try a separate battery to rule out interference from the charging circuit as well.<br /><br />Thanks for the advice,<br /><br />Al

 

[swist]

Re: Depth finder loses bottom with engine running?

A key quesion is whether this was ever working right or is this a recent problem. <br /><br />Assuming the former, the prop wash and flow patterns at the transom of a boat are highly variable. Is it possible you have it mounted in just the wrong place to be seeing only turbulence when the boat it moving? The mounting locations are only a guide. Any chance of trying it in a different lcoation?

 

[murphini]

Re: Depth finder loses bottom with engine running?

I have the exact same problem with the exact same Humminbird unit and replied to a similar post about 3 weeks ago. All answers seem to be...um...rewire. Although I do like a post someone had about putting ferrite beads around the power source to hopefully kill the interference.

 

[alvargo]

Re: Depth finder loses bottom with engine running?

Here's an update and a little more info about the unit and installation. The unit was installed on the boat when I received it last season. It worked better then... it would read bottom when cruising slowly, but would lose it when getting up to plane. The transducer height likely needed adjustment but I didn't mess with it. The problem gradually got worse to the point it would only read when moving very slowly. Now it won't read at all with the engine running even with the boat standing still at anchor. Engine off... reads bottom...engine started in neutral... no bottom reading. It will read bottom while coasting with the engine off or drifting. I didn't try to fix anything until this new problem with not reading the bottom with the engine running.<br /><br />It was then that I re-wired directly to the battery and checked and cleaned the transducer connections with no change.<br /><br />The only change to the engine was replacing the plugs last season. I checked today and verified I installed the QL77JC4 Radio Suppression plugs. I saved the old plugs... they were L77JC4 non suppression plugs. I'm guessing then that the plugs weren't the problem. <br /><br />I brought down a second battery that I will use just for the Humminbird and will try that the next time I take the boat out. If it works with the isolated battery I will try to find some sort of filter. I never heard of the ferrite beads?<br /><br />Thanks for all your suggestions,<br /><br />Al

 

[alvargo]

Re: Depth finder loses bottom with engine running?

I took the boat out with a separate battery for the humminbird wide 100. There was no change to the problem. The bottom reading still disappeared when the engine was running like before. However, I ran the boat in a different location and discovered I would get a reading when deeper than 20 feet of water? It read fairly consistent until the depth dropped below that. With the engine off and drifting it would read bottom at all depths most of the time. <br /><br />I think I just need to get a better unit... I don't know what else to try.

 

[rickdb1boat]

Re: Depth finder loses bottom with engine running?

Is your transducer wire anywhere near another wire going to the engine? This will cause the symptoms you describe. Especially if it's a high voltage wire... Could also be the transducer is just shot...

 

[alvargo]

Re: Depth finder loses bottom with engine running?

Rick,<br />The transducer wire runs along the opposite side of the boat than the engine wiring. I'm not sure how old this unit is but it could be the transducer is getting tired. I don't think I have another one around to try though.. The transucer is much smaller than the humminbird unit on my other small boat.<br /><br />Thanks,<br /><br />Al