Mercury/Mariner Tacho Rev Counter dead?

[Daibheid]

I went and got the Mercury workshop manual for the 2002 90HP 3 cylinder 2 stroke and it has nothing on Diagnostics for the Analog guages. So if anyone could tell me what the resistance/voltage readings or inputs to the tacho should be I'd be grateful as my mates analog rev counter appears to be dead.

I'd rather check it and the engine wiring to find out what exactly's wrong rather than simply tell a friend to go buy a new guage and hope that'll sort it!

[Nos4r2]

Originally Posted by Daibheid

I went and got the Mercury workshop manual for the 2002 90HP 3 cylinder 2 stroke and it has nothing on Diagnostics for the Analog guages. So if anyone could tell me what the resistance/voltage readings or inputs to the tacho should be I'd be grateful as my mates analog rev counter appears to be dead.

I'd rather check it and the engine wiring to find out what exactly's wrong rather than simply tell a friend to go buy a new guage and hope that'll sort it!

Is it the Teleflex or Ultraflex unit (they are the same)?

[Daibheid]

Originally Posted by Nos4r2

Is it the Teleflex or Ultraflex unit (they are the same)?

Not sure Nos - I don't have it anywhere near me but from memory it looks like this one
http://www.gulfstreamshop.com/Images...s/150/2901.jpg
if that makes it any clearer.
The engine wiring diagram shows a gray wire is the sense wire so it'd be good to know what that should show ignition on and then engine running just in case it's a rectifier or charging issue. Apparently the battery doesn't go flat but I have to qualify that with it never went flat when the rev counter was known to be working before the boat went into hibernation and I only ran it briefly on muffs.
TIA for any suggestions

[9D280]

Tacho inputs are usually +, -(or 0V) & Signal.

meter on DCV - Ign off = 0V or thereabouts, on = 12-ish. (Once the engone is running, the usual array of charging voltages should be seen.)

then put meter to ACV, engine off = 0V, engine on will give a variable reading which will bear absolutely no relation to anything of use, but will, if it changes as you rev up & down, at least prove your alternator is throwing something out. (I say no relation as some DVMs get confused a bit if you show them AC that isn't 50Hz).

[uncle al]

purple =ign live
black= earth
grey =tacho signal from rect/regulater

[jyasaki]

Originally Posted by 9D280

(I say no relation as some DVMs get confused a bit if you show them AC that isn't 50Hz).

And sinewave.

jky

[Nos4r2]

It's the teleflex/ultraflex unit if it looks like that.

From memory if you give it a + and - straight from the battery, the needle should move to 0 rpm. If it doesn't, it's gubbed. No point in stripping it, just replace.

[Daibheid]

Thanks 9D280, uncle al, jyasaki and Nos that's all good solid info.
It's all pointing toward my initial conclusion that to use Nos's technical term it's gubbed. Purple black and grey were all wired correctly I metered it DC at 0 ignition off and about 11V ignition on. The fact the needle doesn't budge at ignition on had me thinking it's dead. I should of course have metered it running and as has been pointed out for AC but it's in Winter storage -the kind that has the windscreen off and A-frame unbolted and laid on the console to get it in a shed plus kayaks, grannies, etc stashed in it so getting it out to run it on muffs is a problem hence the enthusiasm for a diag check on the guage itself.

I'll get it run and checked when it comes out of the shed and meanwhile issue the "start saving for a new meter" caution in suitably sympathetic tones. I'll report back when/if I get it sorted.

[Daibheid]

Useful one stop shop detail here on debugging various types of tachometers /rev counter

Troubleshooting Teleflex Tachometer Gauges

[9D280]

Other option - do you know anyone with an engine that is near water? Probably easier to tremove the gauge, test it on another boat, and if it is gubbed, you don't need to take it out the console twice!

[uncle al]

if its any help, with the merc/mar/quicksilver anologue tacho when you switch off the obm, say it was running at a thousand rpm the needle will stay at a thousand untill you switch the ign back on then the needle will drop to zero

[Daibheid]

Thanks 9D280 and uncleal. There are no other Merc engines available to compare with.

After poring over the wiring diag and noting the tach signal comes from the regulator/rectifier this was bugging me enough to do the 130 mile round trip to take another look at it. I had that nagging doubt I was going to find a charging problem if I could run it in the shed.

Here's the actual tacho and the needle looks like this ignition off and on. It did give a tiny shiver to the needle on ignition on/off hinting the tacho may not be dead. Three buckets and a hose followed by a lot of mopping but got it running in the shed.

First attempt to turn it over suggested a low battery and then it wouldn't spin. Ominous sign of a dud battery or one that hadn't been getting charged when the engine was running. Jumped it with a fresh battery and metered no voltage rise with the engine revs. With the booster attached it just sat at 12.6, without the booster battery 11.6. In both cases same as battery voltage with ignition off.


Further inspection found the battery positive lug crimp defective - the wire simply pulled out of the lug. I reckon the positive could easily have disconnected the battery with the engine running. In my experience that's instant death for the reg/rectifier and worst case also the lighting coil side of the Stator.

Forgot to meter for AC on the sense wire but was fading fast due to exhaust fumes and pretty sure I wouldn't find any signal.

Next step is to test the reg/rectifier and the stator but pretty sure I'll be at least ordering Mercury 892115-001 or equivalent.

[uncle al]

team tip Mercury/Marina products never use any p/n that you see on a componant because nine times out of ten that is just a production p/n sometimes they are the same, not very often though always use the OBM serial number to be on the safe side

[Daibheid]

Latest on this I had a Mercury expert come run the proper diagnostics. The stator AC section is shorted to ground. He could test that statically but will need a good stator to test the rectifier/regulator but reckons it's likely gone too. Stator on the way so this rev counter issue is going to be a very expensive fix.

Interestingly he did find what probably caused the carnage - the postive battery terminal crimp had never crimped the conductor and the heavy cable could just pop clean out. It's certain death for the charging electronics of any modern engine in any vehicle if the battery disconnects while the engine is running.

It all took him about 15minutes so good value there except for a few hours travel time

Another interesting nugget/question. The engine had recently had a full service and checkover by a main dealer. IMHO he really should have spotted a basic issue like a poor battery connection. Thoughts?

So two lessons for us here:
1) when routinely checking battery terminals for security,corrosion etc, loss of contact can be very, very expensive and way beyond a failure to start at the quayside.

2) a dead tachometer on at least a Mercury/Mariner is a a real danger sign that you may not be charging your battery and may be unable to key start your engine after shutting down or accidentally kill-cording it

That said, many of us have fishfinders or GPSs at least some of which allow you set minimum voltage alarms. You should set them!
Also as a last resort many outboards have a manual pull-cord start facility. Make sure you know your's and have the cord and the tools to get at the flywheel.

[Daibheid]

Here's a picture of the offending terminal showing how the crimped cable had never been sound. When visually inspected it looked fine but a simple tug on the cable revealed the likely culprit for what will be a hefty repair bill.

The fact the red ancillary power leads shown to the left of the heavy lug ran direct from the battery clamp to the lights/instruments/radio etc meant there would be no indication when the engine was running that the engine battery feed had disconnected briefly/partially/etc.