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Topic: Tachometer

in Forum: C3 Electrical


Tachometer

Posted: 11/13/06 7:53pm Message 1 of 12
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Macon, GA - USA
Joined: 11/11/2006
Posts: 6
Vette(s): 1980. 330 hp 350 been sitting for 3 yrs, so everything needs to be rebuilt or replaced.

How can I tell if the printed circuit is bad on the 1980 tach and console guages or if there is a wiring problem?




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Tachometer

Posted: 11/13/06 8:22pm Message 2 of 12
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
First, Welcome to the Shark Tank!!

Do any of the gauges work? The tach board is separate from the console gauge board, so if all of them are not working, I would be looking at a wiring problem(ground), or possibly a fuse/fuse link.
I can send you a wiring diagram, if that would help. It does have the schematics for the circuit boards, I think...
It does have the console gauge board. The tach board is actually mounted on the back of the tach.
P/M me with an e-mail address, and I'll shoot ya the diagram.

A lot of times, when the tach doesn't work, it is the filter, by the dist. If you unplug it, and the tach works, the filter needs to be replaced. It is in/on the white wire, and supplies the rpm signal to the engine computer.Adams' Apple2006-11-13 20:26:46


Joel Adams
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Tachometer

Posted: 11/14/06 7:15am Message 3 of 12
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Macon, GA - USA
Joined: 11/11/2006
Posts: 6
Vette(s): 1980. 330 hp 350 been sitting for 3 yrs, so everything needs to be rebuilt or replaced.
Thanks for the offer, but I have a wiring diagram and as best I can tell there should be a white wire from the tach to the distributor. This was unplugged so after scrounging around found what could be a white wire from the harness, but it also could be brown or yellow. I plugged it in and tach is still stuck at 4k and moves very slightly when the car is turned on. The center gauges, oil stays pegged at max, temp doesn't seem to work, ampmeter works, gas works. If there is a way to test these before I spend money on printed circuits or gauge rebuilds I would prefer to do that.



Tachometer

Posted: 11/14/06 7:23am Message 4 of 12
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
This may be silly, but...have you checked the fuses? The tach normally sets at 3-4000 when the key is off, I think. When it is powered(key on) it should go down to read correct RPMs. The other gauges not reading correctly would tend to support a no power/ground issue. Then again, it could be a problem in the ign. switch.
I'd suggest a good check of all the fuses with a meter/test light, before condemning the boards. As I said, the two gauge packs use separate boards...hard to believe they would both go bad at the same time, or that one bad one would effect the other.


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Tachometer

Posted: 11/14/06 1:59pm Message 5 of 12
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Joined: 8/16/2005
Posts: 242
have you taken the console out...then you can check with a multimeter or maybe you can already see if some on the "wires" are broken on the circuit

the console with the temp, oil , clock etc gauges is quite easy to get out... one big plug on the back and don't forget the one on top ( light on console)


art-corvette





Tachometer

Posted: 11/14/06 5:43pm Message 6 of 12
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Greensburg, IN - USA
Joined: 9/24/2003
Posts: 5188
Vette(s): Previous: 1984 Silver / Charcoal Coupe, 1988 Maroon Coupe / 1989 Artic White Coupe / 2001 Speedway White Roadster / Present:1976 Stingray Black / Black, Auto, 350 slightly modified (355 hp) Luxor Wires Redline Tires. / 1989 Roadster Bright Red...
[QUOTE=Adams' Apple] First, Welcome to the Shark Tank!!

Do any of the gauges work? The tach board is separate from the console gauge board, so if all of them are not working, I would be looking at a wiring problem(ground), or possibly a fuse/fuse link.
I can send you a wiring diagram, if that would help. It does have the schematics for the circuit boards, I think...
It does have the console gauge board. The tach board is actually mounted on the back of the tach.
P/M me with an e-mail address, and I'll shoot ya the diagram.

A lot of times, when the tach doesn't work, it is the filter, by the dist. If you unplug it, and the tach works, the filter needs to be replaced. It is in/on the white wire, and supplies the rpm signal to the engine computer.[/QUOTE]

Hey bro can ya fire me that diogram? My tach haint nair worked. I'm a workin on da C5 raight now but hit haint gonna tak me all winnter.

                                    thankee! Tux...


Tachometer

Posted: 11/14/06 7:40pm Message 7 of 12
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Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
no...


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Tachometer

Posted: 11/17/06 8:17am Message 8 of 12
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Badin Lake, NC - USA
Joined: 4/21/2004
Posts: 101
Vette(s): 1979 Red L-48 Corvette with Doeskin interior, 3-speed automatic, 3.55 rear; 1986 L-98 Coupe, 4+3 Manual - Satin Black and Purple (SCCA TT/Hillclimb Car); 1993 White LT-1 Coupe, Black Interior, 6-speed
Just a quick note on the O/P reading at MAX - mine did the same thing and it was the sending unit. BTW - if you go to the stupid auto parts stores, they will often look up the Vette and give you a sending switch (for an idiot light). The sensor for the guage looks like a small beer can.  Best to take in the old one to compare. 


C3: 1979 Corvette Coupe, Auto, L-48, Red/Doeskin (my wife's fave);
C4s: 1986 C4 coupe (SCCA road race car), satin black, 4+3, Z51 package, L-98;  & 1993 C4 coupe, white, 6-speed, LT-1.

Tachometer

Posted: 11/17/06 3:18pm Message 9 of 12
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Greensburg, IN - USA
Joined: 9/24/2003
Posts: 5188
Vette(s): Previous: 1984 Silver / Charcoal Coupe, 1988 Maroon Coupe / 1989 Artic White Coupe / 2001 Speedway White Roadster / Present:1976 Stingray Black / Black, Auto, 350 slightly modified (355 hp) Luxor Wires Redline Tires. / 1989 Roadster Bright Red...
[QUOTE=sfindlan] Just a quick note on the O/P reading at MAX - mine did the same thing and it was the sending unit. BTW - if you go to the stupid auto parts stores, they will often look up the Vette and give you a sending switch (for an idiot light). The sensor for the guage looks like a small beer can.  Best to take in the old one to compare.  [/QUOTE]

Mine did OP gauge did the same thing and you are dead on about the auto parts dude. I went to a Car Quest store and that is exactly what happened. Unfortunitly I didn't take the 1st one out prior to going because I was out of town when it decided to start puking oil out of the end. So I had to drive back to the store and they were out of the right one. He was good enough to make a few calls for me and locate one for me so it worked out.



Tachometer

Posted: 11/18/06 6:58am Message 10 of 12
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HOWELL, NJ - USA
Joined: 5/18/2004
Posts: 6812
Vette(s): 1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.
The tach board (which is a pc board) is often the culprit - but not always. It was a gamble in my C3 as well as a few friends - we were 100% successful. In every case, the tach seemed to "float" around a certain RPM and bounce a litttle in reaction to RPM. Replaced the tach board and worked like new. The tach board is a $60 investment and can be replaced by taking the tach out from the front of the dash. No contortionist work under the dash for this one....Tongue
 
But, like I mentioned, definitely a bit of a gable unlesss you are very confident that your wiring is good...



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