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2000 Kia Sephia, 2001 Kia Sephia, 2005 Kia Rio, 1994 Mercedes E320, 1997 Mercedes E320
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Discussion Starter #1
Can anyone give me insight on why my tachometer works whenever it wants? I have the Haynes manual and it doesn't cover anything about the tach. Neither does kiatechinfo.

Is it the coil or maybe a loose wire behid the dash?

Any help will be greatly appreciated.
 

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2004 Optima 2.4 EX, 2005 Yamaha R1 (street) 2001 GSXR 1000 (track)
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I think the tach gets the signal from the crank sensor, maybe the cam sensor, but I don't think the engine would run if one of these sensors was bad. Could be a loose connector, poor ground, of something wrong with the instrument cluster. Did you check the wiring diagram on Kiatech?
 

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2000 Kia Sephia, 2001 Kia Sephia, 2005 Kia Rio, 1994 Mercedes E320, 1997 Mercedes E320
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Discussion Starter #3
Thanks for the quick feedback Matty. I looked at the wiring diagram as you suggested but it's all Chinese to me! I have no clue what I'm looking at. Can you point me in the right direction?
 

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2015 Buick Verano "Leather Group", 2015 Kia Optima Hybrid
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First of all, please title your post with an appropriate title, pertaining to your issue.
You will get more replies, I wasn't even going to look at it, but had to tell you about titles.
The tach gets its signal from the ECU not behind the dash. Thats just the connection from the ECU.
It might be loose at the back of gauge or at the ecu.
 

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2000 Kia Sephia, 2001 Kia Sephia, 2005 Kia Rio, 1994 Mercedes E320, 1997 Mercedes E320
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Discussion Starter #5
Thanks for the quick reply. I will look into it tommorow. There are no engine lights on and all other gauges and meters are working correctly. So you think that the wire going into the tach behind the dash is loose?
 

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2015 Buick Verano "Leather Group", 2015 Kia Optima Hybrid
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Could be or loose at the ecu. Have you touched the coils? I think they might also play a role in the tach reading.
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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New issue

My Wife's "KiaStein" has developed the same issue this week...

Where is the Sensor that sends the RPM Readings from the Engine to the ECU / instrument cluster?

I can not access KiaTech info.

Kind Regards.
 

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2008 SpectraSX, 2014 Optima LX,2006 Jeep Liberty, Linux Mint Mate
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The Input shaft speed sensor is mounted on the transmission and sends the RPMs of the engine to the ECM/ECU.. The ECM then sends the signal to the tach and the TCM.
Dave
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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This past weekend, I did several tests with the "KiaStein" regarding that Randomly failing Tachometer.
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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Weird Tachometer Behaviour under analysis.

I drove the "KiaStein" this past weekend, for a 200 Miles round trip, I wanted to see by myself the Tachometer's Behaviour; and what I've found is:

► Sometimes when the Engine is Started, the Tachometer Works, and Sometimes when engine is Started it doesn't work. This seems to be Randomly happening.

► If the Tachometer works when the Engine is Started, it remains working Flawlessly all the Trip, untill you shut down the Engine, or:

► If the Tachometer works when the engine is Started, it stops working immediately, droppin' the needle to zero; if I switch On, a high power consumption device, such like the Headlamps and / or the Air Conditioner; and the Tachometer returns to Work normally a second after I shut those devices Off, and I accelerate the Engine.

So I bet that the "Random" fail must have something to do with the (in)famous weak wiring / weak Grounding on these Second Gen Sephias.

I'll investigate further and try to clean the Ground connections around the Fuse & Relay Box, and the ECU, to see if that solves the problem.

Beside that Tachometer needle dying and coming to life randomly, the whole car is working Flawlessly and does not developed any other problem, nor shifting related problems so far...

Kind Regards.
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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I removed all the plugs from the wiring at the engine bay, and carefully cleansed them, using electrical contacts cleaner in spray, then allowed to dry and re-plugged everything back together... Everything looked good.

Nothing Changed.
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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So, I decided to buy a new TSS from the Local Kia Dealer:





It looks a little "Different" from the older one:

 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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I installed it Yesterday, with no avail...


The issue continues being the same.
 

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1985 Subaru Loyale (wagon), 2000 Kia Sephia (sedan), and 1969 Mercury Comet (coupé)
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Long years ago, I noticed that the Second Gen Sephia, only has one thick wire coming from the Battery's Negative (Ground) Terminal, directly to the Car's Body. I thought it was weak grounding which becomes weaker as car ages, and I decided to place a second negative wire, directly from said terminal, to the engine. The car has been running Flawlessly like that.

Now, I'm thinkin' of installing a Third Negative wire, this time from said terminal, to the Automatic Transmission's body, specifically to the same bolt where an incoming ground wire comes from the Body...
 

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If the car is running and shifting OK the old sensor sensor is probably OK...
Depending on the make/year/model of car the tachometer may be just a voltage reading device (like an analog DC volt meter) or it may be a servo motor that receives count up/down pulses... Yours is probably the first (reads/displays a DC voltage)...

Because it is a mechanical device it may become intermittent all by itself and your observations of "other things" going on may be a coincidence and not related...
It's a guess as to what is causing it to be intermittent...wiring...sensor...the tach itself.

The car uses that sensor to make other decisions on shifting... to see them... disconnect that sensor and take it for a drive... Shifting points will probably be the first thing you notice.. You should "see" that "if" the sensor was really bad these problems would also be there when the tach was acting up...

I'm tending to believe you "might" just have a bad tach display...
Dave
 

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Steps to Find the Cause

If the car is running and shifting OK the old sensor sensor is probably OK...
I Agree with You; the car is Shifting smoothly and has not developed any kind of fail, other than the Tachometer randomly working / non working.



... the tachometer may be just a voltage reading device (like an analog DC volt meter) or it may be a servo motor that receives count up/down pulses...
It is interesting, that the TSS is named: "Pulse Generator" by Kia, as you can read in its Box, pictured above, so...

... Yours is probably the first (reads/displays a DC voltage)...
...I believe it is not designed as an analog DC volt meter, I believe it reads the Pulses.



... It's a guess as to what is causing it to be intermittent...wiring...sensor...the tach itself...
Yes, you're Right. So, I am checking all the posibilities, one by One, until I find the Culprit.

I've done this so far:
.
  1. Cleansing the Wires, Plugs & electrical connections: Done!
  2. Changing the TSS with a Brand new unit: DONE!
  3. Cleansing the Ground wire connections: DONE!
 

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Electrical False Contact?

Despite that I already cleansed the Ground wire's connections, and changed the old bolt with a new one, the random fail continued; so this...

... I'm tending to believe you "might" just have a bad tach display...
...might be the problem; but the Whole instrument cluster is newer than the Car, I changed it Years ago in order to obtain a Tachometer (The original instrument cluster didn't had it) which is very important for me, Remember this thread?

~► http://www.kia-forums.com/2g-1998-2001-sephia/84797-instrument-cluster-swap-tachometer.html

The newer instrument cluster worked completely Flawlessly for Years; So I believe that the issue could be caused by Electrical False contact on the wirings related to the Tachometer.


"Electrical False Contact" = Means when a Fuse or Bridge wire is proven to be good / alright (Passing current from one of its sides to the other) but its ends / terminals are loose and \ or have enough corrosion to don't let the current to flow as it should, flowing intermittently or not flowing at all.

Kind Regards.
 

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Despite that I already Cleansed the Ground wire connections, I will add a third (extra) Ground Wire (as explained above) to the Transmission, this weekend; in order to be isolating all the possible causes, one by one, 'till I find the Culprit.

Kind Regards.
 

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The TSS does in fact output pulses that change in count with RPMs...
BUT....
The ECM reads these pulses and calculates the proper voltage to put out to the tach.

Microcomputers work in "0"s and "1"s (binary digital) and not in a continuosly variable analog world... The ECM "needs" to change the variable analog RPMs into "bits" (0+1) that it CAN process. We (humans) live in and need an analog world..

Microcomputers use devices called DACs and ADCs (digital to analog /analog to digital converters) to "listen and talk" in our analog world...

We can't easily understand "01000111001001001000011" we need to see a needle pointing at an analog number.. so the ECM "converts " the binary information to a varying analog voltage and the tach (DC meter) moves to display that voltage as a calculated number on the display...

So the tach "may" be a digital (binary) device that counts the binary pulses and displays the result by a stepped motor or it may be a volt meter that reads by magnetic replusion to an analog voltage...

Just because the sender outputs pulses does not mean the tach directly uses those pulses.. There has to be some interpretation done with sender information..
The input speed sensor signal is used for other purposes...(cruse control, ABS, tach, traction control) and that binary data is processed differently for each function..
That data is NOT sent directly to these devices but is processed first and then possibly converted from "A to D" or from "D to A"

Take for example the "output speed sensor"
The output speed sender needs to be corrected for the different size tires (via software) before that information is displayed on the speedometer otherwise larger and smaller tires would read the same but the car would be traveling at quite different speeds..

The tach IS a mechanical device that moves, has friction, and wears out (eventually failing).. Two identical devices will not fail at the same time.. Yours may fail sooner than the next guys.. I would not discount the possibility of the tach failing...

I being an electronic/computer tech (with mechanical thrown in for good measure) have to live and analize "problems" in both worlds (analog and digital). Cars and this world is no longer simply mechanical or analog. We need to understand a mechanical "flaw" OR a digital "bug" can create the same symptom.
Dave
 
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