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 Post subject: tach jumping
 Post Posted: Thu Mar 19, 2009 6:25 pm 
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changed ignition system from msd 6al to msd digital 7. i have the entire system under the dash and the coil is in the car attached to the firewall.. coil is about 10-12 inches away from the box.. problem is the tach needle jumps all over the place..when the car is first started it is fine but after about 20-30 minutes running the tach plays up.. could it be that the tach terminal is picking up interference from the coil and if so how can i shield it..


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 Post subject: Re: tach jumping
 Post Posted: Thu Mar 19, 2009 6:29 pm 
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What coil are you using??? Digital systems require a different coil...

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 Post subject: Re: tach jumping
 Post Posted: Thu Mar 19, 2009 8:15 pm 
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I had a problem with my Digital 7 also and it turned out that the coil was too close to the box!! Have you looked at the RPM graph from that MSD box? If the tach is jumping around I'll bet the graph shows the same s**t. BTW, 10 to 12 inches is too close Bubba! I moved mine and the problem was solved.

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 7:55 am 
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RFI interference does some weard stuff, i would move the coil further away and see if it goes away, do not forget that plug wires and spark plugs also cause these problems if they are not resistor or go bad.

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 8:18 am 
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zephyrc wrote:
changed ignition system from msd 6al to msd digital 7. i have the entire system under the dash and the coil is in the car attached to the firewall.. coil is about 10-12 inches away from the box.. problem is the tach needle jumps all over the place..when the car is first started it is fine but after about 20-30 minutes running the tach plays up.. could it be that the tach terminal is picking up interference from the coil and if so how can i shield it..


Interference is the main suspect here for sure, like mentioned above move it away.

Also which coil ?

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 8:58 am 
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The Digital systems are hard on plugs and wires and it has to have a resistor wires!! Anyone ever get hit with one???? It will knock you on the floor O:) O:)

Funny but my coil is right next to the box #-o

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 10:58 am 
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nlmsc33 wrote:
i get the part about "noise" doing weird stuff... it just seems odd that it would work fine for 30 minutes & THEN go nuts.


hey, I only work for about 30 min and start going nuts.. =; =; and that is one looong 1/4 mile.. =;

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 1:16 pm 
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h am using the hvc coil as required .. both the coil and box are under the dash in the car.. this is a road car and gets used a lot.. i was told to place the coil inside the car to protect it from the heat in the bay,, if i put it in the bay will it really go faulty fairly quick or have i been misinformed.. is it possible to shield it somehow


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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 20, 2009 6:43 pm 
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Get some shielded cable for the tach. use one core for the signal wire and ground the shield back to a ground on the box. although you have seperation between the coil and the box make sure the wiring is not in close proximity, make it longer if required.

if you need some good shielded cable give me a shout with how long and I'll send you some.

As a test you could try wrapping it in some silver foil that often will have the same effect.

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 Post subject: Re: tach jumping
 Post Posted: Sat Mar 21, 2009 1:42 pm 
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thanks sam,, will try the foil shield first and will let you know.. whilst on the subject of digital 7 ign,, is it possible to tune the box using the handheld programer or are there some things it cannot do.. i ask because the other day i managed to trigger my nitrous to test it with the bottle etc off and the ign on... later on i realised that it should not have worked as the rpm limit should have been working.. checked it on the handheld programer and it shows it as being off.. can i turn it on using the handheld unit or must i take the laptop to it..


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 Post subject: Re: tach jumping
 Post Posted: Sun Mar 22, 2009 1:30 pm 
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sorted out the programming on the digital 7..


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 Post subject: Re: tach jumping
 Post Posted: Mon Mar 23, 2009 2:18 am 
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zephyrc wrote:
sorted out the programming on the digital 7..


Post it on here, could help someone else out ?

I've got a 7AL but not the digital version

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 Post subject: Re: tach jumping
 Post Posted: Thu Mar 26, 2009 1:14 pm 
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if i place the coil in the engine bay will it be affected by the heat.. this is on a road car that can be running for 2-3 hours at a time.. sam all i did was read the instructions properly,, all 50 odd pages .. glad i did


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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 27, 2009 10:48 am 
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Most stuff is built to take temperature, having said that you are probably building some extra heat in there without anywhere cool to mount it. you'd be surprised at how much cooler it would run with some simple heat shields around it..

Have you got anything to measure temperatures? sticky strips would do, stick them where you would like to mount it and try it for a while and see how hot it gets, I'll take a look and see what I have in the workshop or I could lend you a hand held thermocouple reader and thermo couple and you could get an idea of how hot that location will be..

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 Post subject: Re: tach jumping
 Post Posted: Fri Mar 27, 2009 12:15 pm 
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thanks very much for the offer sam.. will see if i can get some heat sensitive strips and will let you know.. i had the coil from my 6al in the bay for 11 years with no problem at all. i was thinking of putting the hvc coil in exactly the same place, but i will check the heat first..


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