Motor runs rough with tach wire hooked up
 

This problem popped up after a trip to the mechanic and he suggested
that it might take some time $$ to diagnose. Hopefully someone has
seen this before. I've got a 1982 Mercruiser 140 (181) that developed
a rough disposition after a few minutes on the water recently. It
started 'coughing' at planing speed and then idled bad to the point of
stalling, even back on the trailer. While the engine would be
sputtering, the tach would show the opposite of what was going on, ie:
when the engine would nearly stall the tach would jump up erratically
and alternately nearly bottom out when the rpm's rose. I found that if
I disconnected the tach connection on the coil, the engine idled and
cruised normally. The wire goes from the coil, through the
throttle/shifter and then to the tach. To eliminate (or verify) that
the tach itself might be the problem, I disconnected it at it's end
and reconnected the coil end. The rough engine returned immediately.
Without tearing out the wiring, I'm guessing a short or disconnection
in the throttle area but don't really know what to expect once I'm in
there. Has anybody any suggestions or experience with such a problem?

Thanks,
Ed

Motor runs rough with tach wire hooked up
 

On 17 Feb 2004 02:40:53 -0800, (Ed
Barchetta) wrote:

This problem popped up after a trip to the mechanic and he suggested
that it might take some time $$ to diagnose. Hopefully someone has
seen this before. I've got a 1982 Mercruiser 140 (181) that developed
a rough disposition after a few minutes on the water recently. It
started 'coughing' at planing speed and then idled bad to the point of
stalling, even back on the trailer. While the engine would be
sputtering, the tach would show the opposite of what was going on, ie:
when the engine would nearly stall the tach would jump up erratically
and alternately nearly bottom out when the rpm's rose. I found that if
I disconnected the tach connection on the coil, the engine idled and
cruised normally. The wire goes from the coil, through the
throttle/shifter and then to the tach. To eliminate (or verify) that
the tach itself might be the problem, I disconnected it at it's end
and reconnected the coil end. The rough engine returned immediately.
Without tearing out the wiring, I'm guessing a short or disconnection
in the throttle area but don't really know what to expect once I'm in
there. Has anybody any suggestions or experience with such a problem?

Here's a couple of suggestions, although these might not be the
answer.

Check the wire along it's route for abrasion, cracked insulation, etc.
You might also want your mechanic to test the coil. Pull the tach and
try it on another engine. I would suspect either the tach itself or a
short somewhere along the wiring route.

I'm not familiar with the throttle system you use, but I have worked
on a similar age Merc throttle control and I believe the tach wire,
along with temp sensor, oil pressure etc., went to a connector block
and then to the instruments. Pull the connector apart and check for
corrosion, shorts, etc.

Common sense when looking and if necessary, making a drawing of what
you take apart if you take something apart, is a good idea.

Good luck.

Later,

Tom
S. Woodstock, CT
----------

"Fisherman are born honest, but they get
over it." - Ed Zern

Motor runs rough with tach wire hooked up
 

Or, you could run a new wire, bypassing the throttle, straight to tach.
You really need the manual with wiring diagram to sort it out the right way.

-W

"Short Wave Sportfishing" wrote in message
...
On 17 Feb 2004 02:40:53 -0800, (Ed
Barchetta) wrote:

This problem popped up after a trip to the mechanic and he suggested
that it might take some time $$ to diagnose. Hopefully someone has
seen this before. I've got a 1982 Mercruiser 140 (181) that developed
a rough disposition after a few minutes on the water recently. It
started 'coughing' at planing speed and then idled bad to the point of
stalling, even back on the trailer. While the engine would be
sputtering, the tach would show the opposite of what was going on, ie:
when the engine would nearly stall the tach would jump up erratically
and alternately nearly bottom out when the rpm's rose. I found that if
I disconnected the tach connection on the coil, the engine idled and
cruised normally. The wire goes from the coil, through the
throttle/shifter and then to the tach. To eliminate (or verify) that
the tach itself might be the problem, I disconnected it at it's end
and reconnected the coil end. The rough engine returned immediately.
Without tearing out the wiring, I'm guessing a short or disconnection
in the throttle area but don't really know what to expect once I'm in
there. Has anybody any suggestions or experience with such a problem?

Here's a couple of suggestions, although these might not be the
answer.

Check the wire along it's route for abrasion, cracked insulation, etc.
You might also want your mechanic to test the coil. Pull the tach and
try it on another engine. I would suspect either the tach itself or a
short somewhere along the wiring route.

I'm not familiar with the throttle system you use, but I have worked
on a similar age Merc throttle control and I believe the tach wire,
along with temp sensor, oil pressure etc., went to a connector block
and then to the instruments. Pull the connector apart and check for
corrosion, shorts, etc.

Common sense when looking and if necessary, making a drawing of what
you take apart if you take something apart, is a good idea.

Good luck.

Later,

Tom
S. Woodstock, CT
----------

"Fisherman are born honest, but they get
over it." - Ed Zern

Motor runs rough with tach wire hooked up
 

"Clams Canino" wrote in message news:WTmYb.204648$U%5.1126945@attbi_s03...
: Or, you could run a new wire, bypassing the throttle, straight to tach.
: You really need the manual with wiring diagram to sort it out the right way.
:
:
That's what I'd do...
You already isolated the problem to the wiring - so the next step would be
to inspect the loom and see if there's an abrasion problem and how many
other wires will be affected sooner or later - then go enjoy the water.

Dave

Motor runs rough with tach wire hooked up
 

You might want to chech the shift interupter switch to see if it might be
defective or stuck if your setup has one.

Motor runs rough with tach wire hooked up
 

"Kenneth670" wrote in message
...
You might want to chech the shift interupter switch to see if it might be
defective or stuck if your setup has one.

I wonder if that's the part that my mechanic was referring to. Is this what
prevents you from going into gear with the rpm's too high and located in the
throttle area? If so, that should be easily replaceable and not too
expensive, eh?

Ed

Motor runs rough with tach wire hooked up
 

Good suggestions from all, thank you. This gives me something to get going
on and hopefully diagnose.

Ed

"Ed Barchetta" wrote in message
om...
This problem popped up after a trip to the mechanic and he suggested
that it might take some time $$ to diagnose. Hopefully someone has
seen this before. I've got a 1982 Mercruiser 140 (181) that developed
a rough disposition after a few minutes on the water recently. It
started 'coughing' at planing speed and then idled bad to the point of
stalling, even back on the trailer. While the engine would be
sputtering, the tach would show the opposite of what was going on, ie:
when the engine would nearly stall the tach would jump up erratically
and alternately nearly bottom out when the rpm's rose. I found that if
I disconnected the tach connection on the coil, the engine idled and
cruised normally. The wire goes from the coil, through the
throttle/shifter and then to the tach. To eliminate (or verify) that
the tach itself might be the problem, I disconnected it at it's end
and reconnected the coil end. The rough engine returned immediately.
Without tearing out the wiring, I'm guessing a short or disconnection
in the throttle area but don't really know what to expect once I'm in
there. Has anybody any suggestions or experience with such a problem?

Thanks,
Ed

Motor runs rough with tach wire hooked up
 

"Clams Canino" wrote in message
news:WTmYb.204648$U%5.1126945@attbi_s03...
Or, you could run a new wire, bypassing the throttle, straight to tach.
You really need the manual with wiring diagram to sort it out the right
way.

-W

That's basically what I'm doing now as far as bypassing the throttle. This
works except for the problem of not being able to get out of gear quickly if
necessary and of course the lack of a tach. I'll see if I can find a wiring
diagram online.

Thanks,
Ed

Motor runs rough with tach wire hooked up
 

"Short Wave Sportfishing" wrote in message
...

Here's a couple of suggestions, although these might not be the
answer.

Check the wire along it's route for abrasion, cracked insulation, etc.
You might also want your mechanic to test the coil. Pull the tach and
try it on another engine. I would suspect either the tach itself or a
short somewhere along the wiring route.

I've already eliminated the coil from the equation so it's between the coil
and the throttle. The visible wiring looks good with no cracks. I'll have to
get into the throttle area to examine the connections/wire.

I'm not familiar with the throttle system you use, but I have worked
on a similar age Merc throttle control and I believe the tach wire,
along with temp sensor, oil pressure etc., went to a connector block
and then to the instruments. Pull the connector apart and check for
corrosion, shorts, etc.

I can't remember what my guy called it but the 'switch' inside the throttle
area that stops you from being able to go into gear while the rpm's are too
high may be related. By disconnecting that system at the coil, we run ok,
although after any length of high speed run (25 mph and 3500 rpm), I have to
slow to trolling speed for about a minute before I can get it back into
neutral or manuever into a dock.

Common sense when looking and if necessary, making a drawing of what
you take apart if you take something apart, is a good idea.

Good luck.

Later,

Tom
S. Woodstock, CT
----------

"Fisherman are born honest, but they get
over it." - Ed Zern


Thanks for the reply. We're supposed to get a break in the rain by midweek
so I'll hopefully get to work on it in a day or two.

Ed

Motor runs rough with tach wire hooked up
 

"David Ward" wrote in message
ink.net...
snip
You already isolated the problem to the wiring - so the next step would be
to inspect the loom and see if there's an abrasion problem and how many
other wires will be affected sooner or later - then go enjoy the water.

Dave

Sorry for my ignorance, but what's the 'loom'?

Ed