Another Tach Problem
Thread Starter
Intermediate
Joined: Aug 2009
Posts: 35
Likes: 0
Another Tach Problem
I've read through most of the threads here and can't find one that I can use to find the source of my current problem.
I've got a nice 79, L-82, had it for over 15 years. I've changed a few things in it nothing major, got rid of the emission junk, put on a holly double pumper and a new manifold ect. It usually runs very good but when I got it out this spring it had a miss. I thought it might just be moisture so I took it out to get it warmed up and blown out. The tach worked but when I got on it the tach stopped working. The needle doesn't go to zero it. I looked at smoe of the Wilcox diagrams but mine does not have a filter. The wire goes from the distributor through the firewall. I don't know where bit goes from there. I'm wondering if there is a fuse or a fusable link somewhere or if I might have damaged the innition module when I took it out. I hate to go fooling around under the dash without some very good information. I'm going on 62 years old and getting under the dash usually means a lot of pain.
Any help will be very much apreciated by my wife, myself and my doctors.
I've got a nice 79, L-82, had it for over 15 years. I've changed a few things in it nothing major, got rid of the emission junk, put on a holly double pumper and a new manifold ect. It usually runs very good but when I got it out this spring it had a miss. I thought it might just be moisture so I took it out to get it warmed up and blown out. The tach worked but when I got on it the tach stopped working. The needle doesn't go to zero it. I looked at smoe of the Wilcox diagrams but mine does not have a filter. The wire goes from the distributor through the firewall. I don't know where bit goes from there. I'm wondering if there is a fuse or a fusable link somewhere or if I might have damaged the innition module when I took it out. I hate to go fooling around under the dash without some very good information. I'm going on 62 years old and getting under the dash usually means a lot of pain.
Any help will be very much apreciated by my wife, myself and my doctors.
Former Vendor
Joined: Apr 2009
Posts: 766
Likes: 3
From: Charlotte North Carolina 704-394-5150
First off...the tach filter is mounted on the intake manifold and the wire coming out of your main wiring harness conntects to the tach filter...then the tach filter plugs into the distributor cap.
Sounds like your tach is gone. The speedo/tach cluster is easily removable...so you can check if your printed cirtcuit board on the back of the cluster has a problem in it.
Check your fuse and make sure it is good. If it is...sounds like your cluster may need to be removed...or remove the tach and check your circuits to the tach and see if they are OK.
Information about removing the tach should be on the forum....if not...call me and I can walk you through this. Takes about 10 +/- minutes.
"DUB"
Sounds like your tach is gone. The speedo/tach cluster is easily removable...so you can check if your printed cirtcuit board on the back of the cluster has a problem in it.
Check your fuse and make sure it is good. If it is...sounds like your cluster may need to be removed...or remove the tach and check your circuits to the tach and see if they are OK.
Information about removing the tach should be on the forum....if not...call me and I can walk you through this. Takes about 10 +/- minutes.
"DUB"
Le Mans Master
Joined: Mar 2001
Posts: 6,638
Likes: 287
From: Ann Arbor Michigan
I just replaced the Tach circuit board in my 78'. Here's the instructions that came with it. Note the "problems" section. On mine, I think the real problem was corrosion of the terminals that the circuit board plugs into. I installed the new board anyway since I had it and it now works great. I removed the whole cluster since I wanted to check the big connector from the back, but you don't have to.
Gary
Gary
Cruising
Joined: Oct 2009
Posts: 12
Likes: 0
tach problems.... i recently sent mine off after replacing the circuit board to only find that didnt solve the problem. the actual tach needed to be restored. during my troubles i found this out:
My coil was bad. it worked enough to start the engine but was completely bad on the Tach side.
Filter was bad. replaced that.
now i have proper voltage at the dash location. when you take you tach out. you will see three (3) prongs.
LEFT is ground.
TOP is battery (key on)
RIGHT is the feed from the Dizzy. you should have voltage when engine is running. disconnect from the Dizzy while the car is running and voltage should be zero (0). that way you can check for a cross.
i didnt have voltage on that prong which made me change the filter. still didnt have voltage so i changed the coil. have voltage now so i bought a circuit board - STILL NO TACH. thats when I realized the tach itself was bad.
in my case more than likely that coil spiked and blew it out. my circuit board was burnt.
the fuse is good and all other gauges work. when that fuse goes out, you will know it - all the gauges act funny.
ramsey
My coil was bad. it worked enough to start the engine but was completely bad on the Tach side.
Filter was bad. replaced that.
now i have proper voltage at the dash location. when you take you tach out. you will see three (3) prongs.
LEFT is ground.
TOP is battery (key on)
RIGHT is the feed from the Dizzy. you should have voltage when engine is running. disconnect from the Dizzy while the car is running and voltage should be zero (0). that way you can check for a cross.
i didnt have voltage on that prong which made me change the filter. still didnt have voltage so i changed the coil. have voltage now so i bought a circuit board - STILL NO TACH. thats when I realized the tach itself was bad.
in my case more than likely that coil spiked and blew it out. my circuit board was burnt.
the fuse is good and all other gauges work. when that fuse goes out, you will know it - all the gauges act funny.
ramsey
Last edited by ramseygarza; Oct 30, 2009 at 12:53 PM.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
tach problems.... i recently sent mine off after replacing the circuit board to only find that didnt solve the problem. the actual tach needed to be restored. during my troubles i found this out:
My coil was bad. it worked enough to start the engine but was completely bad on the Tach side.
Filter was bad. replaced that.
now i have proper voltage at the dash location. when you take you tach out. you will see three (3) prongs.
right is ground.
top is constant battery (key on)
left is the feed from the filter. you should have voltage when engine is running. disconnect from the Dizzy while the car is running and voltage should be zero (0). that way you can check for a cross.
i didnt have voltage on that prong which made me change the filter. still didnt have voltage so i changed the coil. have voltage now so i bought a circuit board - STILL NO TACH. thats when I realized the tach itself was bad.
in my case more than likely that coil spiked and blew it out. my circuit board was burnt.
the fuse is good and all other gauges work. when that fuse goes out, you will know it - all the gauges act funny.
ramsey
My coil was bad. it worked enough to start the engine but was completely bad on the Tach side.
Filter was bad. replaced that.
now i have proper voltage at the dash location. when you take you tach out. you will see three (3) prongs.
right is ground.
top is constant battery (key on)
left is the feed from the filter. you should have voltage when engine is running. disconnect from the Dizzy while the car is running and voltage should be zero (0). that way you can check for a cross.
i didnt have voltage on that prong which made me change the filter. still didnt have voltage so i changed the coil. have voltage now so i bought a circuit board - STILL NO TACH. thats when I realized the tach itself was bad.
in my case more than likely that coil spiked and blew it out. my circuit board was burnt.
the fuse is good and all other gauges work. when that fuse goes out, you will know it - all the gauges act funny.
ramsey
Le Mans Master
Joined: Mar 2001
Posts: 6,638
Likes: 287
From: Ann Arbor Michigan
Cruising
Joined: Oct 2009
Posts: 12
Likes: 0
yeah. i dont know what you mean full of errors.
the 79 has a coil where one side of the dizzy is labeled TACH. that wire goes to the filter. from the filter to the prong behind the tach itself.
remove the Tach - you will see your circuit board and the three prongs: ground , batt, and the feed from the dizzy.
which car are you working on???? we're talking about the 79 vette.
the 79 has a coil where one side of the dizzy is labeled TACH. that wire goes to the filter. from the filter to the prong behind the tach itself.
remove the Tach - you will see your circuit board and the three prongs: ground , batt, and the feed from the dizzy.
which car are you working on???? we're talking about the 79 vette.
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Cruising
Joined: Oct 2009
Posts: 12
Likes: 0
the way to test the actual tach is to REMOVE the circuit board, ground it and place a 12 dc volt source on the prong. the needle will go to in one direction. place the 12vdc on the other prong and the needle will move in the other direction.
it should peg each side. if it moves slow or gets stuck, then that part of the tach is bad and you need to send it off. Ecklers offers the service for around $249.
it should peg each side. if it moves slow or gets stuck, then that part of the tach is bad and you need to send it off. Ecklers offers the service for around $249.
Cruising
Joined: Oct 2009
Posts: 12
Likes: 0
check out this link for the schematic of your tach
http://www.corvetteforum.net/c3/tune.../index18.shtml
very helpful
ramsey
http://www.corvetteforum.net/c3/tune.../index18.shtml
very helpful
ramsey
