Help with tach repair

[law086]

Hey all,

Hoping you might be able to help me get my tach working on my boat. It's an '03 350 MAG MPI.

Tach currently moves to zero when it's powered up, but doesn't read RPMs when engine is running.
The tach was working earlier this season. According to my captain (my kid), he said it was working, then stopped, then started again in a later outing, then stopped again. I can't confirm that since I didn't see it myself, but I do know it was working earlier this season and now it's not working.

I went ahead and ordered a new tach, hooked it up, still doesn't work.

Checked continuity of the ground from the wire at the tach to the negative side of the battery and got 2 ohms, which seems fine. Just to be sure we put a wire directly from the negative on the battery to the tach. Still nothing.

The ignition power (the purple wire) at the gauge is also fine. The gauge does show the hour reading and reads the expected volts (almost 12v with the engine off). Just to verify a jumped a 12v from the battery directly to the ignition lead of the tach since it seems like a have a bit of voltage drop on the main wire, but that didn't change anything.

Finally, with a multimeter, we measured AC volts between the tach signal and the ground at the gauge and got constant 2.3v that went up with more RPMs and back down with less RPMs. My understanding is that's the expected result if the signal wire is working correctly.

At this point I'm stumped since it seems as if the signal wire and ground wires are good, and the new tach didn't fix it. Oh, and it's set to 4 pulse, which is the same pulse setting it had when working.

Any advice or thoughts would be awesome.
Thanks!!!

 

[Bondo]

Ayuh,..... Welcome Aboard,...... What motor,..?? What vintage,..??

Got a serial number for it,..??

 

[Scott06]

Hey all,

Hoping you might be able to help me get my tach working on my boat. It's an '03 350 MAG MPI.

Tach currently moves to zero when it's powered up, but doesn't read RPMs when engine is running.
The tach was working earlier this season. According to my captain (my kid), he said it was working, then stopped, then started again in a later outing, then stopped again. I can't confirm that since I didn't see it myself, but I do know it was working earlier this season and now it's not working.

I went ahead and ordered a new tach, hooked it up, still doesn't work.

Checked continuity of the ground from the wire at the tach to the negative side of the battery and got 2 ohms, which seems fine. Just to be sure we put a wire directly from the negative on the battery to the tach. Still nothing.

The ignition power (the purple wire) at the gauge is also fine. The gauge does show the hour reading and reads the expected volts (almost 12v with the engine off). Just to verify a jumped a 12v from the battery directly to the ignition lead of the tach since it seems like a have a bit of voltage drop on the main wire, but that didn't change anything.

Finally, with a multimeter, we measured AC volts between the tach signal and the ground at the gauge and got constant 2.3v that went up with more RPMs and back down with less RPMs. My understanding is that's the expected result if the signal wire is working correctly.

At this point I'm stumped since it seems as if the signal wire and ground wires are good, and the new tach didn't fix it. Oh, and it's set to 4 pulse, which is the same pulse setting it had when working.

Any advice or thoughts would be awesome.
Thanks!!!

did you try cycling it between the cylinder settings. occasionally that can fix a wonky tach

 

[nola mike]

Ayuh,..... Welcome Aboard,...... What motor,..?? What vintage,..??

Got a serial number for it,..??

It's an '03 350 MAG MPI.

 

[law086]

Ayuh,..... Welcome Aboard,...... What motor,..?? What vintage,..??

Got a serial number for it,..??

Thanks. '03 350 MAG MPI. It's on an 03 Chaparral 230SSI with a Bravo 3. I don't have a serial number handy unfortunately as the number is rubbed off on the spark arrester cover

 

[law086]

did you try cycling it between the cylinder settings. occasionally that can fix a wonky tach

Thanks for the thought. We did not, but can try that. Given I have two tachs (the one that was in the boat and one new) that don't work I doubt that'll do it, but it's worth a shot!

 

[Scott06]

Thanks for the thought. We did not, but can try that. Given I have two tachs (the one that was in the boat and one new) that don't work I doubt that'll do it, but it's worth a shot!

probably not with two tachs although you may want to clean the tach signal connections back to the engine including the cannon plug pins and at coil

 

[Scott Danforth]

check continuity on the grey wire

 

[law086]

check continuity on the grey wire

Given that I had voltage on that wire I know it has continuity to somewhere
Where should I grab the other end from? I'm not sure where it goes and it's super hard to tell with all the harnesses.

Thanks!

 

[Scott06]

Given that I had voltage on that wire I know it has continuity to somewhere
Where should I grab the other end from? I'm not sure where it goes and it's super hard to tell with all the harnesses.

Thanks!

it ends up from the dash harness through the cannon plug back ultimately to the coil, not sure if it goes through the ECU on an MPI might need to google a wiring diagram

 

[Scott Danforth]

Given that I had voltage on that wire I know it has continuity to somewhere

there should never be voltage on the grey tach wire. that is the pulsed to ground side of the coil

 

[law086]

there should never be voltage on the grey tach wire. that is the pulsed to ground side of the coil

My understanding is a multi-meter reading AC will read *something* when it's receiving pulses. You can't use DC however since most meters aren't fast enough to register the tach pulses. Is that not correct?

 

[dingbat]

My understanding is a multi-meter reading AC will read *something* when it's receiving pulses.

You are correct....

tach signal characteristics

Can anyone offer me a definitive answer on the nature of the tachometer signal for most outboards?? Take an Evinrude for example, wherein the regulator rectifier supplies the gray wire (tach signal). I'm asking because I don't have an o-scope nor a running engine to test this myself at the...

forums.iboats.com

 

[Scott Danforth]

My understanding is a multi-meter reading AC will read *something* when it's receiving pulses. You can't use DC however since most meters aren't fast enough to register the tach pulses. Is that not correct?

there are a few. Fluke 88 is one but requires an inductive pickup.

you can also wrap a wire around a single sparkplug wire as an inductive pickup, read frequency in HZ, and multiply by 60 to get RPM