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Author Topic: Tach reading about 1200 rpm high across the board?  (Read 629 times)

Offline angelo78

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Tach reading about 1200 rpm high across the board?
« on: January 09, 2017 - 08:26:22 am »
Hi guys,

Just installed a msd tach adaptor to get my factory ralley tach to work with my msd 6a .  Only problem is that it reads about 1200 rpm high across the entire rev range.  Could a faulty resister cause this and could I ad an inline resister?  Anyone got any Other ideas?

Cheers




Offline HP_Cuda

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Re: Tach reading about 1200 rpm high across the board?
« Reply #1 on: January 09, 2017 - 07:45:02 pm »

Are you attaching it to the grey wire?
1970 Cuda Clone 440 4 speed - sublime green
1970 Cuda 383 4 speed - yellow - SOLD

Offline angelo78

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Re: Tach reading about 1200 rpm high across the board?
« Reply #2 on: January 10, 2017 - 09:33:05 pm »
Yes Mate, Grey wire.


Offline dodj

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Re: Tach reading about 1200 rpm high across the board?
« Reply #3 on: January 10, 2017 - 09:41:06 pm »
Did you install the 8290 adapter? Was the tach accurate before the MSD ign? Factory tachs are not noted for their accuracy
Scott
1973 Challenger  440 4 spd 
2007.5 3500 6.7 Cummins Diesel, Anarchy tuned.
Good friends don't let friends do stupid things. ........alone.

Offline angelo78

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Re: Tach reading about 1200 rpm high across the board?
« Reply #4 on: January 10, 2017 - 11:07:03 pm »
Hi Dodj,

Yeah sure it is the 8290 adaptor.

Since I got the car the I have not had the Tacho working until now, so don't really have a baseline to go off. 

Offline dodj

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Re: Tach reading about 1200 rpm high across the board?
« Reply #5 on: January 10, 2017 - 11:22:36 pm »
I plan on installing one of these eventually.
http://rt-eng.com/rte/index.php/RTE_67-74_Tach_kit

If you read the write-up under 'detailed information' it mentions a potentiometer on the original cct board. So it is probably adjustable.
In my mind though, if I have the tach that far apart, might as well put a new board in rather than adjusting the old.  :2cents:
Scott
1973 Challenger  440 4 spd 
2007.5 3500 6.7 Cummins Diesel, Anarchy tuned.
Good friends don't let friends do stupid things. ........alone.

Offline angelo78

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Re: Tach reading about 1200 rpm high across the board?
« Reply #6 on: January 11, 2017 - 02:18:59 am »
Wish i saw that before i bought the tach adaptor. :banghead: :banghead:

Offline dodj

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Re: Tach reading about 1200 rpm high across the board?
« Reply #7 on: January 11, 2017 - 12:49:22 pm »
You and me both. New board is not much more than the adapter.  :eek4:
Scott
1973 Challenger  440 4 spd 
2007.5 3500 6.7 Cummins Diesel, Anarchy tuned.
Good friends don't let friends do stupid things. ........alone.

Offline angelo78

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Re: Tach reading about 1200 rpm high across the board?
« Reply #8 on: January 15, 2017 - 06:57:52 pm »
Update,

Removed the Tacho,  the wave washers behind 2 of the springs had a bit of corrosion on them which effected the alighnment of the shaft to the needle and created a restriction at about the 1500 rpm indicating mark.  I cleaned them up and now have the 0 to 2000 rpm reading correct. It is now 1000 rpm out at the top scale reads 6k when its only 5k.  There seem to be the ability to adjust the return springs so i will have another go tonight.

Cheers

Offline angelo78

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Re: Tach reading about 1200 rpm high across the board?
« Reply #9 on: January 16, 2017 - 07:46:54 am »
Latest update is i adjusted the pot on the factory board and it is now spot on through the entire range.  Was a lot of trial and error but worth the effort👍

Offline dodj

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Re: Tach reading about 1200 rpm high across the board?
« Reply #10 on: January 16, 2017 - 05:05:12 pm »
 :2thumbs:
Scott
1973 Challenger  440 4 spd 
2007.5 3500 6.7 Cummins Diesel, Anarchy tuned.
Good friends don't let friends do stupid things. ........alone.