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Tach acting erratic. 69 dodge #2765544
04/18/20 04:07 PM
04/18/20 04:07 PM
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Detroit
Kidsixpack Offline OP
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I have a monster tach in my 69 bee. The original tach was 900rpm off so I updated it some time ago. The car starts and runs fine. After warming up the tach is jumping around. I haven’t driven it during the erratic behavior yet.
Do you guys think it may be the tach or some sort of electrical gremlin effecting the tach. Where would you look first?
Thanks!
KID

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2765549
04/18/20 04:11 PM
04/18/20 04:11 PM
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Grand Prairie,Texas
stumpy Online content
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Have you changed anything in the ignition since installing the tach?

Re: Tach acting erratic. 69 dodge [Re: stumpy] #2765563
04/18/20 04:52 PM
04/18/20 04:52 PM
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Eagle, Idaho
Neil Online content
The Doctor is in.
Neil  Online Content
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If the tach wire is too close to a spark plug wire it will do what you described. Been there done that....

Re: Tach acting erratic. 69 dodge [Re: Neil] #2765623
04/18/20 07:31 PM
04/18/20 07:31 PM
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Kidsixpack Offline OP
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Nothing new in the ignition system. The tach is wired to the hidden MSD. It’s all been on the car for around ten years.
KID

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2765923
04/19/20 12:55 PM
04/19/20 12:55 PM
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north of coder
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MSD box overheating because it's hidden ? loose/corroded tach connection on box ?
beer

Re: Tach acting erratic. 69 dodge [Re: moparx] #2765961
04/19/20 01:57 PM
04/19/20 01:57 PM
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Detroit
Kidsixpack Offline OP
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Originally Posted by moparx
MSD box overheating because it's hidden ? loose/corroded tach connection on box ?
beer


I will check this.
Thanks
KID

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2781484
06/04/20 07:19 PM
06/04/20 07:19 PM
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Kidsixpack Offline OP
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Still dealing with this issue. Runs well until it gets up to operating temp. Turns out that my cap and rotor both burned up. Swapped them out. still jumping tach. Swapped out the coil. Still jumping tach.
Replaced the distributor, cap and rotor again. Still not fixed. I've suspected the MSD from the very beginning. Swapped in my original Duel Point. Haven't gotten the car started yet so I don't know if removing the MSD from the equation is the fix or not. I'm going to tinker with this for now, but I did pick up another MSD to swap in.
KID

Re: Tach acting erratic. 69 dodge [Re: moparx] #2781500
06/04/20 07:46 PM
06/04/20 07:46 PM
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Originally Posted by moparx
MSD box overheating because it's hidden ? loose/corroded tach connection on box ?
beer


Mine was a loose/high resistance connector right on the negative side of the coil

Obviously looking at it , you sure in the hell couldnt tell when it had full insulation/rubber over terminal end

Didn’t figure it out until I took an ohm meter on the wire itself and had the wife wiggle and bend and move the wire around

And then when I finally took/peeled the insulation off you could see the dark area

Was a bad connection I would assume since new , as it progressively got worse over the years


1E46F73E-52B9-4F82-BF24-EB8CB3F17326.jpeg
Last edited by bee1971; 06/04/20 07:50 PM.

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Re: Tach acting erratic. 69 dodge [Re: bee1971] #2781695
06/05/20 12:28 PM
06/05/20 12:28 PM
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north of coder
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over the years, connections like that have driven me nutz !
glad you found that. up
hopefully, the OP can find his problem and report back.
beer

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2781712
06/05/20 12:43 PM
06/05/20 12:43 PM
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Downtown Roebuck Ont
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Originally Posted by Kidsixpack
Nothing new in the ignition system. The tach is wired to the hidden MSD. It’s all been on the car for around ten years.
KID


Including the Monster Tach?

Kevin

Re: Tach acting erratic. 69 dodge [Re: Twostick] #2781751
06/05/20 02:02 PM
06/05/20 02:02 PM
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Is it possible you're not getting enough juice?

I had this issue a number of years ago.

I had a stock alternator. The issue just kind of crept up on me. Add the msd, add an electric fuel pump, add some more gauges and then, the alternator just could not keep up. Most of the time, mine would do what you're describing. It would not happen until the car was warmed up. The gauge would show that the system was charging good but, the battery was getting low.

Other than the tach, the car never did anything stupid and ran fine. After I would drive it for the day, back on the trickle charger it went; rinse and repeat and the same thing happened for years. The tach was old so; I thought it was just a little finicky.

I can't even remember what finally clued me in to the issue but, I installed a new, higher rated alternator and the issue never happened again.

Maybe check the volts on the battery after driving it? It doesn't take much for electronics to act funny.

Re: Tach acting erratic. 69 dodge [Re: Twostick] #2787269
06/19/20 10:11 PM
06/19/20 10:11 PM
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Kidsixpack Offline OP
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Originally Posted by Twostick
Originally Posted by Kidsixpack
Nothing new in the ignition system. The tach is wired to the hidden MSD. It’s all been on the car for around ten years.
KID


Including the Monster Tach?

Kevin


Yes the tach has been on the car at least as long as the MSD. Planning to try to work on it this weekend, Will update this post.
Thanks
KID

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2787270
06/19/20 10:12 PM
06/19/20 10:12 PM
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Detroit
Kidsixpack Offline OP
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I did find a couple of questionable connections. Repaired them. No change so far. I did this when I replace the Distributor.
KID

Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2787333
06/20/20 09:26 AM
06/20/20 09:26 AM
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God's Country Maryland
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Your tach could be bad. I had an Auto Meter tach go bad years back, the 340 developed a mis and a jumping tach needle that I couldn't track down to any certain cylinder. I replaced all the electrical components in the ignition system, no fix. I disconnected the tach wire and the mis went away. Hooked it back up and the mis came back. It was the tach all along.


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Re: Tach acting erratic. 69 dodge [Re: Kidsixpack] #2787337
06/20/20 09:35 AM
06/20/20 09:35 AM
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Indiana
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Idk about MSD part but my tach has a good ground on the engine instead of the dash frame. Maybe try switching it if its not there already.







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