Merc 150 Tach Acting Weird???

Hey guys I'm new to the forums, but I've been browsing around and I really like the site. It seems like there is a ton of info on this site.

Anyways I've got a 2001 Mako 232 with twin 2001 Mercury 150's (Carberated) with approx 600hrs on them.

A couple months ago the starboard engine's tach started acting really weird. At first it would only go up to about 3000RPM while the engine was definitely reving higher than that b/c I could tell from the port engines tach and having both engines in sync by sound. What was really weird was that if I trimmed the motor up or down then the Tach would show the correct RPM reading.

Now the Tach doesn't work at all. We figured there was a short or a bad tach so we swapped tachs between the port and starboard engines and the port engine's tach still worked while the starboard engine's tach still didn't work so we were able to rule out a bad tach.

I've been told that the voltage regulator might have gone bad, but the Voltage meter is reading a postive charge when the starboard engine is running.

I really don't know what else to do besides double check the connections again. I'm more of a do it yourself kind of person so I don't really want to pay someone to fix it for me, but I really don't know too much about the electrical systems on these outboards.

Any help would be greatly appreciated!

Thanks,
Dan

Re: Merc 150 Tach Acting Weird???

If your 150's are like a pair of '95's I had, you have two voltage regulators per motor and the tach is connected to pulses from only one. The flakely or failed one may be connected to the tach and the other may be OK, hence the normal voltage reading. You need to check both, if your motors have two. The shop manual should be a help. I assume you have one.

Re: Merc 150 Tach Acting Weird???

wilde1j said:

If your 150's are like a pair of '95's I had, you have two voltage regulators per motor and the tach is connected to pulses from only one. The flakely or failed one may be connected to the tach and the other may be OK, hence the normal voltage reading. You need to check both, if your motors have two. The shop manual should be a help. I assume you have one.

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Rojer that. When a voltage regulator fails does it usually fail slowly? If so would that explain the low RPM reading followed later by no RPM reading?

Thanks

Re: Merc 150 Tach Acting Weird???

The part of your story I thought was odd, is that when you trimmed the motor up or down the tach would work again. Maybe you have a loose wire, or one that the outside insulation seems fine but the inner wire is broken. Just a though to check the wires.

Re: Merc 150 Tach Acting Weird???

Raysoncraft16 said:

The part of your story I thought was odd, is that when you trimmed the motor up or down the tach would work again. Maybe you have a loose wire, or one that the outside insulation seems fine but the inner wire is broken. Just a though to check the wires.

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Yeah that's what is really confusing me. We've checked all of the connections and everything looks good.

Re: Merc 150 Tach Acting Weird???

Like Wilde said, son's 150 has 2 regulators located in the center rear of the engine under the plate that the trim relays mount to. The tach is plugged into a gray wire from one of them. Swapping to the gray wire on the other will answer your question. You may need to get some slack from the wiring harness if it's currently plugged into the top one.

If that solves your problem and you still have good charge on your batteries then I would leave it at that.

But each of those rect/regul modules is responsible for 20A max of battery charging (40A total). So even though it may seem that your are charging ok, you may only be charging from one. If you don't run a lot of accessories no biggie. If you do, you might disconnect the one that's GOOD (both yellow wires from stator and tape up to protect) and recheck battery voltage while running, checking for a charge condition. Then you will know. Obviously you'll want to reconnect after your testing.

Mark

Re: Merc 150 Tach Acting Weird???

Texasmark said:

has 2 regulators located in the center rear of the engine under the plate that the trim relays mount to.

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Do you think this could have anything to do with why operating the trim on the motor initially corrected the Tach problem?

Re: Merc 150 Tach Acting Weird???

any other ideas?

thanks

Re: Merc 150 Tach Acting Weird???

I suggest doing some basic troubleshooting using a multimeter (test volts/ohms). Here is a link to a Teleflex web page that provides some guidance on how to troubleshoot tachometer problems. While your tach is probably not a Teleflex brand, the troubleshooting steps and volt/ohm specs should still apply.

Further, I suggest hooking up a voltmeter to the appropriate posts on the back of the tach gauge while operating the boat and seeing what the voltmeter shows when the tach is "acting weird." This should help you narrow down the possible causes.

I hope this helps you.


http://www.teleflexmorse-eu.com/gaugessearch/tech.html

Re: Merc 150 Tach Acting Weird???

Update: Some time ago I addressed this issue on the son's '95 150 in addition to my comments above. Yesterday it finally got a trip to the lake after installing a new tach. Problem solved.

Tach was a Quicksilver from the local Merc dealer......$88. Looks like the old one and blends right in with the other Quicksilver instruments.

Mark

Re: Merc 150 Tach Acting Weird???

Texasmark said:

Update: Some time ago I addressed this issue on the son's '95 150 in addition to my comments above. Yesterday it finally got a trip to the lake after installing a new tach. Problem solved.

Tach was a Quicksilver from the local Merc dealer......$88. Looks like the old one and blends right in with the other Quicksilver instruments.

Mark

Click to expand...

I wish it was the tach, but we tried switching tachs between the starboard and port engine and the port engine's tach still didn't work while the starboard engines tach still did work.

Oh well I'm gonna try some of that troubleshooting tips ya'll offered and go from there.

Thanks

Re: Merc 150 Tach Acting Weird???

Since the trim relays mount on a plate directly over your regulators, there may be some interconnections there. Possibly in the wiring harness where the wires may run adjacent to each other. Don't have it in front of me so I don't know where the trim relay wires are routed.

Mark