TACH Problems help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

lamar · 10-06-2004, 07:40 PM

OK I wired up the tach, one wire to dist. - one wire to the fuse panel( marked ing. unfused. When I crank it up the tach will move with the engine rpms but at I think much lower value, also at idle the tach read o. Do I just need to adjust it with the screw in the back?

1-PU70 · 10-06-2004, 07:47 PM

Did you conect a ground wire?

lamar · 10-06-2004, 07:50 PM

I was thinking it was grounded by the ground wire in the harness. But I did try to ground the thrid prong on the back to a good chasis ground.,

**68 Stepside** · 10-06-2004, 08:26 PM

Need a little more info. Is it an aftermarket tach or a stock tach? V8 or 6 cyl? I'm not saying I can answer all your questions, but I may be able to help.

Brainchild · 10-06-2004, 08:28 PM

If it's an aftermarket,check to see that it is set to the proper cylinder setting.4,6,8 cyl.I bet that's the problem.Some stock tachs have this setting too.
Prolly on the back,may have to remove the cover to get to it

lamar · 10-06-2004, 09:26 PM

Stock tach, new goodwrench performance deluxe 350. It came with dist. wires and plugs. HEI dist,

**68 Stepside** · 10-06-2004, 09:35 PM

If the tach is an original 6 cyl tach, it'll read odd, but I think it should read high

From what I've gathered, there's an adjustment screw on the back of a stock tach that you can mess around with. Use a known good tach of some sort, designed for a V8, and adjust your stock tach accordingly. Best of luck.

Longhorn Man · 10-06-2004, 09:39 PM

I've seen a stock one act like this. I'd rev the sucker to about 3500 RPM and hold it, and the needle would slowly rise to about 1000 RPM.
We chucked it and slapped in an aftermarket one.

lamar · 10-06-2004, 10:08 PM

Thanks guys for the help. Iguess I'll play with the adjustments and see what happens. Just made the normal nightly run to the gro. store and the tach would move a little at normal rpm and speeds around 0-500 but when I hammer it the tach seems to read closer to what it should, but as soon as I let off the gas the tach returns quickly to 0-500 range. Maybe it needs adjusting. Thanks

10-06-2004, 07:40 PM	#1
lamar Registered User Join Date: Apr 2004 Location: Covington,Ga Posts: 453	TACH Problems help OK I wired up the tach, one wire to dist. - one wire to the fuse panel( marked ing. unfused. When I crank it up the tach will move with the engine rpms but at I think much lower value, also at idle the tach read o. Do I just need to adjust it with the screw in the back?

10-06-2004, 07:47 PM	#2
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	Did you conect a ground wire? __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

10-06-2004, 08:26 PM	#4
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,692	Need a little more info. Is it an aftermarket tach or a stock tach? V8 or 6 cyl? I'm not saying I can answer all your questions, but I may be able to help. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

10-06-2004, 08:28 PM	#5
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	If it's an aftermarket,check to see that it is set to the proper cylinder setting.4,6,8 cyl.I bet that's the problem.Some stock tachs have this setting too. Prolly on the back,may have to remove the cover to get to it __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

10-06-2004, 09:35 PM	#7
68 Stepside huh? Join Date: May 2000 Location: Washington, Illinois Posts: 5,692	If the tach is an original 6 cyl tach, it'll read odd, but I think it should read high From what I've gathered, there's an adjustment screw on the back of a stock tach that you can mess around with. Use a known good tach of some sort, designed for a V8, and adjust your stock tach accordingly. Best of luck. __________________ Someday when I'm lonely, Wishing you weren't so far away, Then I will remember Things we said today. RIP El Jay

10-06-2004, 07:50 PM	#3
lamar Registered User Join Date: Apr 2004 Location: Covington,Ga Posts: 453	I was thinking it was grounded by the ground wire in the harness. But I did try to ground the thrid prong on the back to a good chasis ground.,

10-06-2004, 09:26 PM	#6
lamar Registered User Join Date: Apr 2004 Location: Covington,Ga Posts: 453	Stock tach, new goodwrench performance deluxe 350. It came with dist. wires and plugs. HEI dist,

10-06-2004, 09:39 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	I've seen a stock one act like this. I'd rev the sucker to about 3500 RPM and hold it, and the needle would slowly rise to about 1000 RPM. We chucked it and slapped in an aftermarket one.

10-06-2004, 10:08 PM	#9
lamar Registered User Join Date: Apr 2004 Location: Covington,Ga Posts: 453	Thanks guys for the help. Iguess I'll play with the adjustments and see what happens. Just made the normal nightly run to the gro. store and the tach would move a little at normal rpm and speeds around 0-500 but when I hammer it the tach seems to read closer to what it should, but as soon as I let off the gas the tach returns quickly to 0-500 range. Maybe it needs adjusting. Thanks



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