Hello everyone

I just bought a new engine 350/290 HP for my 1977 C3

I had a MSD kit

MSD Ignition 85551
MSD Digital 6AL Ignition 6425

My Tachometer is not working

I had 3 suggestions and I am lost I dont wanna buy something that will not work.

*1 The firs suggestion was told to buy
MSD Magnetic Pickup Tach Adapters 8920

*2 other person told me to buy
ELECTRONIC TACHOMETER / TACH CONVERSION

so I can convert my old Tach



*3 and summit told me to change the Distributor
Summit Racing® Blueprinted HEI Distributors SUM-850001-T


Just to make Sure My vette is 1977 L48 and the new engine is 350/290 Hp

and I prefer to dont change my new MSD Ignition 85551



I did find ELECTRONIC TACHOMETER / TACH CONVERSION but its for 1973 dos that one work on any suggestions

http://www.parts123.com/corvettecent...50g&ukey=27606

Thanks

 

Did you bypass the tach filter? Does that model MSD have a tach port on the box or do the instructions say to hook it to the coil?
I'd bet that electronic tach conversion is for mechanical to electronic.

 

The 6AL dilemma... I'll tell you that I'm removing this kit from my 72 because in my opinion the failure rate is too high. MSD won't tell you this but if you jump start the car (if your battery dies) with the battery terminals connected, you can short out the 6AL box. They know this issue exist and if you call their tech line they will fess up..... but they make no mention of it in their installation instructions. One of my techs jumped my 72 two weeks ago..... and for the second time the box is dead. So for me, I'm going to switch over to my original distributor and run the pertronix ignition kit.

So.. back to your issue.

Like Tim said, bypass the filter and see if you the tach works... Unplug A and plug it into the tach port or the distributor.



My 72 is a mechanical drive tach so I've never explored the MSD set up. But if you call them, find out if the box has a signal terminal and what the square output is... I dn't have a clue what the output is of the MSD box, but I do know what is required to drive the original electronic tachometer. I'm pretty sure there is a terminal on the 6AL box on the side and maybe someone that has done this in the past will chime in and possibly post the output of the box.

The other issue... you don't need to convert your tach, your tach is already an electronic tachometer so it's possible you have an issue with the board in the tach.

So with this in mind, I'd pull the plug from the back of the tachometer and see if with the key on, you have power and ground at the tach connector. Use a known ground to test for power... if you have power, then use the ground in the connector to test again. This will verify the ground if you do it this way.



If you have power and ground, then verify continuity from the connector input wire to the connector that plugs into the tach filter. A to B in the picture above.

If you need to remove the tachometer, use these instructions.... it's the easiest way to get the tach out of the car. http://repairs.willcoxcorvette.com/w...ad-removal.pdf

Willcox

 

TimAT & Willcox Corvette
Thank You both of you I really appreciate it. I will check the car the car today it's at a god shop in MD I will follow up.
Thanks

 

I've had an msd-6a box in my 68 for 20+ years (on and off) and haven't had a problem with it. I've run it with multiple different ignition systems-mallory distributor, ramjet gm distributor, MSD 8572 corvette tach drive distributor(required for that guy), and now with the locked out MSD (tach drive removed & dist locked out) and EZ-EFI 2.0. I am not questioning anybody's experience--- just sharing mine.

I have a Corvette electric tach (don't remember if 75, 76, or 77) in it that I installed about 14 years ago. I ended up removing the tach filter and running the output from the msd box directly to the tach. I did this because with the tach filter in place, and when revving the engine above ~3500, then the tach would bounce. I removed tach filter and now the tach is steady at all times from the msd box output.

 

I have the same issue with my 81. Crate motor and MSD distributor. No signal. Tested the board and it works fine.

 

Too many words by me.
1. The tach output of my MSD box is wired directly to my (1976) electric tachometer.
2. No tach filter. (works better when removed)
3. If it doesn't work, then test with an aftermarket tach. Worked on mine. So I then installed the real tach.

 

The tach signal input for the stock board should be a square signal, 16 pulse's per RPM.. The stock board can read a curve to, but the curve signal should also be 16 per RPM.

If the MSD box can do this for output then there is no reason the factory tach would not work with or without the filter. If the MSD box can put this signal out (and I have no idea if it can, only they will know this), then the box will drive the stock tach.

Willcox

 

I want to thank you all. It worked
The gray msd signal hooked to the brown tach wire.