Jumpy Tach needle
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,881
Likes: 9
From: staten island ny
Jumpy Tach needle
I recently installed a flex a lite auxiliary fan on my 79. It's hooked up to a relay so it comes on when the a/c comes on to provide additional cooling. My problem is when turned on my tach needle starts bouncing around. I never had any problem with the tach before and cant figure out why now. Soon as I turn the a/c off the tach returns to normal. Any ideas?
Thx, ESU
Thx, ESU
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Originally Posted by ESU
I recently installed a flex a lite auxiliary fan on my 79. It's hooked up to a relay so it comes on when the a/c comes on to provide additional cooling. My problem is when turned on my tach needle starts bouncing around. I never had any problem with the tach before and cant figure out why now. Soon as I turn the a/c off the tach returns to normal. Any ideas?
Thx, ESU
Thx, ESU
Hey Cory,
I agree that I'd check closely where your tapping off the power for the fans. It sounds like the fan motors are feeding back an AC like signal to the tach board causing it to jump around. I wired the electric fans in my 75 right to the alternator tap to assure I was getting a good connection. I haven't had any issues with my tach FWIW.
If it does turn out to be something wrong w/the tach board, I can help you repairing it vs doing the repro board thing. Let me know if I can be of assistance.
BTW, you done w/the force now? I remeber last fall when Lars was here you didn't have long to go. I hope everything worked out.
Good Luck!
Regards................George
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,881
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From: staten island ny
George and MDJ21,
I'm gonna take a close look at how I wired it. Cant remember for the life of me where I tapped into. Soon as I get a free hour or so I just wanted to see what you guys thought, I was also leaning towrds where I tapped in.
As for the dept, I officially retired March 2006, 20 yrs and 3 months. I started working as a consultant for Lockheed Martin on a big security contract here in the city. I thank you for asking.
I'm in the process of hooking up a new Nordskog digital dash, speed, tach and center guages. Right now all I've completed is the center gauges so just in case my tach is shot I'll be replacing it soon with the digital one. So thanks again for the offer of assistance.
ESU
I'm gonna take a close look at how I wired it. Cant remember for the life of me where I tapped into. Soon as I get a free hour or so I just wanted to see what you guys thought, I was also leaning towrds where I tapped in.
As for the dept, I officially retired March 2006, 20 yrs and 3 months. I started working as a consultant for Lockheed Martin on a big security contract here in the city. I thank you for asking.
I'm in the process of hooking up a new Nordskog digital dash, speed, tach and center guages. Right now all I've completed is the center gauges so just in case my tach is shot I'll be replacing it soon with the digital one. So thanks again for the offer of assistance.
ESU
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
If you getting some sort of spikes on the line from the fans or related circuits, relays etc., you should be able to filter it out with a capacitor. Does your car have a tach filter?? If so maybe it needs replacing, it's purpose is to get rid of unwanted spikes that cause problems. Might be worth a try before resorting to a new tach board.
Thread Starter
Drifting
Joined: Jun 2004
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Likes: 9
From: staten island ny
Originally Posted by bobs77vet
you can always use a relay to get clean power if you need to
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,881
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From: staten island ny
Originally Posted by TopGunn
If you getting some sort of spikes on the line from the fans or related circuits, relays etc., you should be able to filter it out with a capacitor. Does your car have a tach filter?? If so maybe it needs replacing, it's purpose is to get rid of unwanted spikes that cause problems. Might be worth a try before resorting to a new tach board.
ESU
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Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Originally Posted by ESU
What years came with filters and where would it be located?
ESU
ESU
http://www.ecklers.com/product.asp?p...dept%5Fid=1135
I had a bouncy tach above 2k rpm, mine was old and ready to fall apart, after installing a new one the tach is smooth again.
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Originally Posted by TopGunn
75-89. It's located just to the left side of the dist., bolted to the intake manifold. Here's a link with a picture.
http://www.ecklers.com/product.asp?p...dept%5Fid=1135
I had a bouncy tach above 2k rpm, mine was old and ready to fall apart, after installing a new one the tach is smooth again.
http://www.ecklers.com/product.asp?p...dept%5Fid=1135
I had a bouncy tach above 2k rpm, mine was old and ready to fall apart, after installing a new one the tach is smooth again.
This is certainly worth checking too. If you need a filter and don't care about originality, one can be easily built for far less than buying a repro. Again let me know.Glad to hear no more NYC streets for you. And good for you on the consulting gig.
More $$$ for the vette, huh? 
Again good luck troubleshooting and let us know what you find.
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,881
Likes: 9
From: staten island ny
Originally Posted by TopGunn
75-89. It's located just to the left side of the dist., bolted to the intake manifold. Here's a link with a picture.
http://www.ecklers.com/product.asp?p...dept%5Fid=1135
I had a bouncy tach above 2k rpm, mine was old and ready to fall apart, after installing a new one the tach is smooth again.
http://www.ecklers.com/product.asp?p...dept%5Fid=1135
I had a bouncy tach above 2k rpm, mine was old and ready to fall apart, after installing a new one the tach is smooth again.
ESU
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Originally Posted by ESU
I've had my maifold off 2 or 3 times and dont recall ever seeing that part. Might have been taken off when the prior owner hooked up the MSD. Where does it wire into? 1st tho I'm going to look into where I tapped into for 12 v.
ESU
ESU
Cory,
Not sure if it's different on a MSD, but on a stock system one end of the filter goes to the tach output on the distributor. The other end goes to the tach. Also the case has to be grounded.
If you want I'll send you a homebrew filter you can use. If you use the original tach or an aftermarket digital, you likely should have a filter in line to protect the tach itself from any electrical spikes, etc.
I still have your address from the video so say the word and a filter will be on it's way.
Last edited by ACECO; Jul 7, 2006 at 12:16 PM.
Drifting
Joined: May 2005
Posts: 1,629
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From: Somers CT
Originally Posted by ESU
I've had my maifold off 2 or 3 times and dont recall ever seeing that part. Might have been taken off when the prior owner hooked up the MSD. Where does it wire into? 1st tho I'm going to look into where I tapped into for 12 v.
ESU
ESU
Bill
Thread Starter
Drifting
Joined: Jun 2004
Posts: 1,881
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From: staten island ny
Originally Posted by ACECO
Cory,
Not sure if it's different on a MSD, but on a stock system one end of the filter goes to the tach output on the distributor. The other end goes to the tach. Also the case has to be grounded.
If you want I'll send you a homebrew filter you can use. If you use the original tach or an aftermarket digital, you likely should have a filter in line to protect the tach itself from any electrical spikes, etc.
I still have your address from the video so say the word and a filter will be on it's way.
Not sure if it's different on a MSD, but on a stock system one end of the filter goes to the tach output on the distributor. The other end goes to the tach. Also the case has to be grounded.
If you want I'll send you a homebrew filter you can use. If you use the original tach or an aftermarket digital, you likely should have a filter in line to protect the tach itself from any electrical spikes, etc.
I still have your address from the video so say the word and a filter will be on it's way.
Thx ESU
Drifting
Joined: May 2005
Posts: 1,629
Likes: 4
From: Somers CT
Originally Posted by Bob Onit
$62.99 
I would love to know whats inside that little sucker
It looks like nothing more than a carbon choke
I would love to know whats inside that little sucker
It looks like nothing more than a carbon choke
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Originally Posted by Bob Onit
Can you test a cap for its value? mf,pf ect?
Not an electrolytic. Actually it's two caps and two resistors. .1uf, 100pf, 5.6K and 10K ohm. Basically a bandpass filter I believe. I have a schematic somewhere. Let me find it and I'll post it later.