Wacky Speedometer

[beachedredneck]

Newbie, so please forgive me if I missed an answer to this in a previous thread.

I've got a 1993 115 TLRR that has the digital pro series gauges installed. The speedometer/fuel gauge shows my fuel level (I think it's right) after repairing the ground but the speedometer is a lot less friendly.

When turning the key on, speedometer starts off at 55mph then gradually climbs until it hits about 74-75mph. It does this with the water hose attached or disconnected. Trying to find manuals or information on anything pre 1994 has been tough and I'm out of ideas.

Is it possible that a less than great ground could cause the issue?

Bad power connection?

Is the gauge just shot?

Any help is appreciated.

[throrope]

I suspect your speedometer works similar to ours and uses a water port on the leading edge of the lower unit connected to the speedometer by a small diameter hose. As speed builds, the water pressure on the port increases and the speedometer shows a higher speed.

If like ours, the port collects crap. The fix is clearing the port with thin soft wire . While a pain to access, the hose connection and hose closest to the outboard may also require clearing. Since we primarily run skinny water, this happens so often, I use the GPS and the speedo plugs the hole in the console.

Beyond that, by far the single reason for gauge problems is bad connections, typically ground and especially for the tachometer. before buying parts, I suggest sequentially checking every connection and fuse with liberal application of WD40 and cold brew. Use the WD40 on the boat.

[TownsendsFJR1300]

Looking at the lower unit parts fisch of your engine it does, as noted above, appear to be water pressure operated (part #69):

1993 115TLRR Yamaha Outboard LOWER DRIVE 1 Diagram and Parts

If you look at the back of your speedometer, you should see a rubbery/plastic line, maybe a little larger than .25" coming off it.

The system is designed for water pressure to be pushed in from the pitot hole (a very, very small hole in the lower unit), up thru a hose, then pressurize the speedometer hose eventually activating the speedometer.

As noted above, the lower unit hole tends to corrode and clog up, especially in salt water and brackish water.

IF, your boat set up is as described, couple things to do to fix it.

Coming about 2' from the engine is a plastic connector that connects the engine hose to the "hull" hose.

Simply pull that connector apart. If its clogged, the speedometer will now likely drop to 0 MPH.

Using a very small drill bit, being EXTREMLY GENTLE (its very easy to break the drill bit off), slowly work it into the pitot hole (which is right on the leading edge of the LU).

Alternatly, while doing that as well, take a small funnel, slip it over the hose at the top of the engine and squirt water from a hose nozzle down the tube.

Once its clear, water will flow easily from tha pitot tube.

Maintainance after that will require simply flushing the pitiot hole with a hose, with a a sharp cut "V" in it. The V slips over the hole, pressurize with fresh water and let it drain/squirt back out.

While the hose is off at the speedometer and at the engine end, again, squirt some water DOWNWARDS from the speeometer end to the engine to clear any debris, old water from that line.

If you have an air compressor, you can also use that (low pressure, maybe 20 PSI) to blow out that line and the engine line as well.

I have since hooked up a "T" connector and a shrader valve inside the center console of my boat. After I flush with fresh water, I hook up a small 12volt air compressor, snap it on the shrader valve, turn it on and watch ALL the excess water come out the pitiot tube. Since doing this, the speedometer has been accurate down to 4 MPH (where it won't register anymore-normal operation).

*The hose I use with the "V" cut, is simply an old washer machine hose, female end(for the garden hose nozzle) with a sharp "V" cut to fit over the leading edge. Cheap and works great...

Please post your findings / results.

[beachedredneck]

Would either of these fixes help the fact that even with the water hose disconnected the speedometer is reading between 50 and 75mph?

[TownsendsFJR1300]

Would either of these fixes help the fact that even with the water hose disconnected the speedometer is reading between 50 and 75mph?

If it is a WATER pressure speedometer and the hose is disconnected, something is wrong with the speedometer itself. There's nothing else left.

I'd pull the speedometer and peek inside where the hose would go, perhaps some slight air pressure might save it. Somethings stuck or corroded inside

If its corroded inside, I don't know if you can open it up without destroying it. A new head would be needed..

[beachedredneck]

Greatly appreciated. I know I can't take it apart, but I'll try flushing it out with fresh water and see what happens. Definitely a water pressure speedo, definitely sealed so it can't be opened.

[TownsendsFJR1300]

Greatly appreciated. I know I can't take it apart, but I'll try flushing it out with fresh water and see what happens. Definitely a water pressure speedo, definitely sealed so it can't be opened.

Yep, you really don't have much to lose at this point.

If you have access to an air compressor, I would try that first (low PSI), water never actually makes it that far up, the water in the tube, forcing the air pressure up, would be making the needle move (in short, water shouldn't be in there)

You never know, could just be a small piece of crap in an orifice inside the unit.

Good luck and please post what happens..

[theflats]

Looking at the lower unit parts fisch of your engine it does, as noted above, appear to be water pressure operated (part #69):

1993 115TLRR Yamaha Outboard LOWER DRIVE 1 Diagram and Parts

If you look at the back of your speedometer, you should see a rubbery/plastic line, maybe a little larger than .25" coming off it.

The system is designed for water pressure to be pushed in from the pitot hole (a very, very small hole in the lower unit), up thru a hose, then pressurize the speedometer hose eventually activating the speedometer.

As noted above, the lower unit hole tends to corrode and clog up, especially in salt water and brackish water.

IF, your boat set up is as described, couple things to do to fix it.

Coming about 2' from the engine is a plastic connector that connects the engine hose to the "hull" hose.

Simply pull that connector apart. If its clogged, the speedometer will now likely drop to 0 MPH.

Using a very small drill bit, being EXTREMLY GENTLE (its very easy to break the drill bit off), slowly work it into the pitot hole (which is right on the leading edge of the LU).

Alternatly, while doing that as well, take a small funnel, slip it over the hose at the top of the engine and squirt water from a hose nozzle down the tube.

Once its clear, water will flow easily from tha pitot tube.

Maintainance after that will require simply flushing the pitiot hole with a hose, with a a sharp cut "V" in it. The V slips over the hole, pressurize with fresh water and let it drain/squirt back out.

While the hose is off at the speedometer and at the engine end, again, squirt some water DOWNWARDS from the speeometer end to the engine to clear any debris, old water from that line.

If you have an air compressor, you can also use that (low pressure, maybe 20 PSI) to blow out that line and the engine line as well.

I have since hooked up a "T" connector and a shrader valve inside the center console of my boat. After I flush with fresh water, I hook up a small 12volt air compressor, snap it on the shrader valve, turn it on and watch ALL the excess water come out the pitiot tube. Since doing this, the speedometer has been accurate down to 4 MPH (where it won't register anymore-normal operation).

*The hose I use with the "V" cut, is simply an old washer machine hose, female end(for the garden hose nozzle) with a sharp "V" cut to fit over the leading edge. Cheap and works great...

Please post your findings / results.

photos please !

[TownsendsFJR1300]

photos please !

Photo's of what specifically?