TACH reading 3 times higher - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dano69c10 · 05-18-2005, 12:11 PM

The tach on my '79 c30 454 is reading 2100 at idle and maxes out when I'm driving around. I thought this only hooked up to the HEI distributor. The wire looks fine, any help on this? Are there any other wires to look at?
Thanx in advance
Dano

82c10 · 05-18-2005, 12:21 PM

check the ground, make sure it is grounded good , we undid the screw that held my ground on and the tach maxed out.

ocbaud · 05-18-2005, 12:30 PM

what kinda tach is it? if its an aftermarket tach it possibly could have a setting for 4, 6, and 8 cylinders. it its set to a lower setting, it will do what you're saying.

but being as you have a c30, i'm guessing it has a stock tach in it?

Dano69c10 · 05-18-2005, 12:48 PM

Stock TACH, where's the ground?
Dano

ocbaud · 05-18-2005, 01:05 PM

i'm not sure about the ground problem or if its something else. i dont know where the ground wire leads to on the stock tach, i do know that most of the stock tachs are not very accurate and need to be rebuilt. how long has it been reading off? has it ever read correctly?

Russell · 05-18-2005, 02:09 PM

That is one of the signs of a tach headed south -- Reading too high... You can check out www.73-78.com for more information.

I hate to leave a plug, but I do have a spare one that'd look real nice in there for sale on the parts board, lol

82c10 · 05-18-2005, 05:33 PM

i believe he meant, www.73-87.com, i asked my auto service teacher, he said it's either a ground, which your going to have to look at wiring schematics to find out where it should be, or like Russell said it's about to quit

Russell · 05-18-2005, 06:56 PM

thanks for the correction 82c10 -- I just type too fast for my own good, lol

f.monroe · 05-18-2005, 09:15 PM

Look above the left (drivers) kick panel .There should be a gang connector and the tach ground hooks to the top of it . It is just a female blade connector . The wire comes off of the instrument panel on the back side of the tach . There are only three wires , 12 v , Ground , and ignition which goes to the distributor . If you look under the dash you will see the wires . You might also want to check all of the under hood frame and body grounds . Frank

Dano69c10 · 05-19-2005, 01:19 PM

Thanx everyone! I'll look at it this weekend.
Dano

Hoods69BadBowTie · 05-19-2005, 02:48 PM

My buddy had a stock tach doing the same thing for a little while, ground did not fix it and then it was shot. Got a nice aftermarket one and no problems since then.
-Later

77gmcjoe · 05-19-2005, 09:32 PM

Quote:

Originally Posted by Hoods69BadBowTie

Got a nice aftermarket one and no problems since then.
-Later

Ya gotta love them factory tachs, though.
It's usually the first thing I look for when I see an interior pic.

And yeah, I've seen them reading high when they're going bad.

05-18-2005, 12:11 PM	#1
Dano69c10 Senior Member Join Date: Jan 2005 Location: Ontario, Kali Posts: 2,427	TACH reading 3 times higher The tach on my '79 c30 454 is reading 2100 at idle and maxes out when I'm driving around. I thought this only hooked up to the HEI distributor. The wire looks fine, any help on this? Are there any other wires to look at? Thanx in advance Dano __________________ '69 Fleet It ain't yours, if you didn't build it!

05-18-2005, 12:48 PM	#4
Dano69c10 Senior Member Join Date: Jan 2005 Location: Ontario, Kali Posts: 2,427	Stock TACH, where's the ground? Dano __________________ '69 Fleet It ain't yours, if you didn't build it!

05-18-2005, 02:09 PM	#6
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	That is one of the signs of a tach headed south -- Reading too high... You can check out www.73-78.com for more information. I hate to leave a plug, but I do have a spare one that'd look real nice in there for sale on the parts board, lol __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

05-18-2005, 06:56 PM	#8
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	thanks for the correction 82c10 -- I just type too fast for my own good, lol __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

05-19-2005, 01:19 PM	#10
Dano69c10 Senior Member Join Date: Jan 2005 Location: Ontario, Kali Posts: 2,427	Thanx everyone! I'll look at it this weekend. Dano __________________ '69 Fleet It ain't yours, if you didn't build it!

05-18-2005, 12:21 PM	#2
82c10 needin' money Join Date: May 2005 Location: Chickasha, Oklahoma Posts: 1,106	check the ground, make sure it is grounded good , we undid the screw that held my ground on and the tach maxed out.

05-18-2005, 12:30 PM	#3
ocbaud Garage Queen Material Join Date: Oct 2002 Location: USA Posts: 4,129	what kinda tach is it? if its an aftermarket tach it possibly could have a setting for 4, 6, and 8 cylinders. it its set to a lower setting, it will do what you're saying. but being as you have a c30, i'm guessing it has a stock tach in it?

05-18-2005, 01:05 PM	#5
ocbaud Garage Queen Material Join Date: Oct 2002 Location: USA Posts: 4,129	i'm not sure about the ground problem or if its something else. i dont know where the ground wire leads to on the stock tach, i do know that most of the stock tachs are not very accurate and need to be rebuilt. how long has it been reading off? has it ever read correctly?

05-18-2005, 05:33 PM	#7
82c10 needin' money Join Date: May 2005 Location: Chickasha, Oklahoma Posts: 1,106	i believe he meant, www.73-87.com, i asked my auto service teacher, he said it's either a ground, which your going to have to look at wiring schematics to find out where it should be, or like Russell said it's about to quit

05-18-2005, 09:15 PM	#9
f.monroe Senior Member Join Date: May 2004 Location: Caldwell,Tx. Posts: 3,648	Look above the left (drivers) kick panel .There should be a gang connector and the tach ground hooks to the top of it . It is just a female blade connector . The wire comes off of the instrument panel on the back side of the tach . There are only three wires , 12 v , Ground , and ignition which goes to the distributor . If you look under the dash you will see the wires . You might also want to check all of the under hood frame and body grounds . Frank

05-19-2005, 02:48 PM	#11
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	My buddy had a stock tach doing the same thing for a little while, ground did not fix it and then it was shot. Got a nice aftermarket one and no problems since then. -Later __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!!



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