Tachometer showing high rpm


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rogerg1955
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Tachometer showing high rpm

Postby rogerg1955 » Mon Feb 03, 2014 11:24 pm



I have 88 gl1500 I bought three months ago.
Rode it home 50 mi tach worked fine.did routine
Winter maintence filters,fluids,etc. new battery
Started up often tach showed perfect.
Rode first time today 55mph in 5 th gear it would red line
I've read the other post. Clutch is not slipping,
Radiator full,ground terminals tight.
PS at normal idle the tach shows 2000 rpm
"Help please"



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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Tue Feb 04, 2014 9:05 am

I drive a 88 also...my tach works but it would be nice to find out what yours does not...

A brief description...the tach display converts ignition pulses sent to it from the ignition module into a proportional dc voltage that moves the tach needle.....

It's displaying 2 times what it's suppose to....so I can only think of 2 possibilities..
Either the ignition module is sending 2X the pulses ot the tach is converting them wrong...

The last idea is a bad ground that operates the meter....

Testing....This will be experimental,but I'll look into it....I'll try various meters on the pulse line from the ECM to see what kind of readings I get..
Do you have any test equipment..eg volt meter(what kind),tach/dwell meter..etc.??

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Tue Feb 04, 2014 3:12 pm

I change filters and some bulbs. I also put a trinkle charger on the right rear pocket.put the ground wire under passenger seat on a ground bolt.
Installing that an the hood is the only thing I've done. Put the seat back on and rode that's when it started. I only have a volt meter but willing to purchase something of it might help.
Thanks for the info and concern virgilmobile

All help is appreciated

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Tue Feb 04, 2014 4:46 pm

Your volt meter...can you post a picture of it that shows the selector switch so I can see the ability of the meter.
Is it analog or digital.?

I'll try to match your meter(I have many) and locate the test points.
I also have a old hand held dwell/tach (never needed) that might be able to "read" the pulses going to the tach and give some display.(Yours if needed).
Something we can come up with should be able to narrow down where the problem might be.
Having the same bike working is handy so we can compare voltages,etc.

Also,the things you've done should not in any way affect the tach.

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Wed Feb 05, 2014 10:30 am

I' m new at this but this is the specs on my voltmete.

Digital voltmeter
Ac/dc 200m-600
Ohm 20m-200
Amp 20-10

Thanks for your interest

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Wed Feb 05, 2014 10:47 am

That's enough to start with.Ill grab my DVM and start.Ill post the results ASAP.

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Wed Feb 05, 2014 2:47 pm

Ok..It's gonna be a day or two before I can do the test I'm thinking of....
It seems that the tach is disconnected(after removing the entire cluster from the dash) then tested by just applying 12 volts DC voltage to its terminals..(see picture)

Here's my idea...To make this easy to test the meter,I'll unplug my ECM...not hard....Use a couple of different batteries..eg 9volt,1.5volt and the bikes battery (12.8volt).
Each voltage should deflect the meter to a different reading...
I'll record each voltage to the meter and it's display then post it.
The book says that battery volts should move the needle "fully"...whatever that means...I assume to the max reading....I'll check this out...
Just to be certain that it is just a DC voltage,I'll look at the signal with a scope for erroneous pulses.
I'll also use the DVM at a idle,about 850 rpm,and measure the voltage on that line....

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Wed Feb 05, 2014 6:23 pm

I read the indication came off the coil on 88 the ecu module later yrs.
I have ordered a tach. Thought it might help. Virgilmobile i need to ride to clean the carbs will i hurt the tach. I would say at 3000 rpm the tach is redlined.

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Wed Feb 05, 2014 9:20 pm

Ill double check the schematics.the one I have shows ECM connection.I can believe it can also come from one coil too.I can't positively confirm either one yet.
Will it damage the tach?Doubtful.its designed to be able to show full scale anyways.
I think mine runs about 3k in OD at 65 mph or so.
I'm sure you can "feel" the engine if its really winding up too high.
It's less than the 1200 and certainly not like a weed whacker engine.
More like a truck engine.You can lug it pretty low.
Your ordered tach...a test tach or replacement?

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landisr
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Re: Tachometer showing high rpm

Postby landisr » Wed Feb 05, 2014 11:07 pm

rogerg1955: While you/we wait for further input from VM, why don't you go back to basics and remove the seat, un-do whatever hookups you installed, leave the seat off and start the bike to see how the tach reads. Like VM says, it doesn't seem logical that your changes should affect the tach, but things went bad right around the time you made your modifications, and good ol' Murphy is always looking for opportunities.... Just sayin'...

Ron in AZ
Beam me up, Scotty. There's no intelligent life down here.

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Wed Feb 05, 2014 11:08 pm

A plug wire induction tach

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landisr
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Re: Tachometer showing high rpm

Postby landisr » Wed Feb 05, 2014 11:11 pm

rogerg: you might have missed my post just above your last reply... Ron
Beam me up, Scotty. There's no intelligent life down here.

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Wed Feb 05, 2014 11:21 pm

I think I'll do that tomorrow
Thanks Ron can't hurt

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Thu Feb 06, 2014 1:54 pm

I still can't get to my bike...It's covered outside while I relocate a new washer and dryer from my shop...AND we have sleet and snow,34* in the sub-tropics no less...I'm so over this cold. :shock:

I have seen diagrams showing the tach getting pulses from a ignition coil pulse line on one schematic...I can't confirm it's for the 88 tho...Perhaps someone has a "real"schematic for the 88..

Another thought...While you look at your bike...can you verify that the tach has a back light(dash light) working.?
It appears that the tach has 3 wires to it...12 volts from relay 3 and fuse 11...It's the black/brown wire..
There's a green ground(suspect) and a pulse wire from one coil...I assume this one is OK because the tach does move with the rpm change...Its possible that the backlight circuit also powers a electronic part in the tach.Check for the backlight....As always a bad ground at the meter can cause weird problems...Usually a bad ground is indicated by multiple anomalies..eg dim lights,flasher problems,gauges don't show right etc....so check all your lights,gauges switch function...see if anything will affect the tach....

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Thu Feb 06, 2014 4:20 pm

Started engine, turned lights out tach iluminated.
Turned off took off seat,remIves wire from fuse panel
I had installed for cell charger,removed wire from top of buse bar
I installed for trinkle charger. No change in rpm.
Tach I ordered is for testing goes around spark plug
Wire

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Thu Feb 06, 2014 4:45 pm

So far you confirmed that the tach has a good ground and 12 volts (backlight working) there nothing else but the pulse wire.

If it comes from a coil the tach is bad,if it comes from the ECM either could be bad.
This is why I need to confirm the wiring first.

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Thu Feb 06, 2014 5:51 pm

34 deg. Fingers getting cold. I' ll
Put it on hold til tomorrow
Thanks millions men

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Thu Feb 06, 2014 8:51 pm

The needle moves with engine rpm just 1000 or so higher.
#8 fuse looks ok tried testing relay seemed good going tO double check tomorrow

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Fri Feb 07, 2014 12:14 pm

GOOD NEWS I HOPE
First I removed # 3 relay check it last night.
Forgot it was out turn switch on hit starter notice no instrument lights
Turned key off inserted relay. Tach works as normal.
I was about to take the dash out. I still have no idea what happened.

I want to thank "virgilmobile and landisr"

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virgilmobile
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Re: Tachometer showing high rpm

Postby virgilmobile » Fri Feb 07, 2014 12:32 pm

Glad to hear.
I can guess what happened.
The relay contacts are corroded.
It supplies enough power to light the backlight(which probably powers the tach electronics) but at a slightly reduced voltage.
If I'm right,your backlight might be just a bit brighter and (I'll have to verify this) if you remove the relay the tach may completely go dead along with the backlight.
Just to be safe,pull the relay and look for signs of corrosion.If none are found,get a spare relay to replace it with.

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Fri Feb 07, 2014 12:54 pm

Sounds logical. I will order a relay.
You have walked me thru this step by step
maybe one day I'll be able to help another

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virgilmobile
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83 GL1100 I
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84 GL 1200 I

Re: Tachometer showing high rpm

Postby virgilmobile » Fri Feb 07, 2014 1:51 pm

Don't special order a relay....OEM can be expensive.
The relay can be replaced with a generic auto relay..take it to NAPA or some such real parts place..
You might find the big box auto store people have no idea what you have.
Expect to pay no more than 5-7 bucks for it too.

Persistence and accurate measurements pays off....good job. :D :D

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rogerg1955
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Re: Tachometer showing high rpm

Postby rogerg1955 » Fri Feb 07, 2014 8:10 pm

Thanks again virgilmobile




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