tach jumping, timing irradic - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 6 Old 09-18-2016, 08:21 AM Thread Starter
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tach jumping, timing irradic

Hi, the other night I had my car out and it started revving high. I looked down and the tach needle was jumping, i put timing light on and timing is jumping all over the place. It's 347/msd 6al/msd blaster coil/msd pro billet dist/autogage tach/summit one wire alt...any input would be greatly appreciated...thanks!


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post #2 of 6 Old 09-18-2016, 10:32 AM
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timing will move all the time, the is what electronic engine management does.

first thing, would be to remove all that msd stuff, return to a quality ford dist, with ford electronics.

the msd and others are known to have junk stator/rotor setups inside.

you could take it to a shop that can scope the primary and secondary wave forms, and it will be clear to the eye.


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post #3 of 6 Old 09-18-2016, 10:41 AM
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The tach jumping around and the engine spark timing acting up points to an ignition pickup problem or a loose connection or bad ground in the system.

It could be anything from the distributor to the MSD 6AL. It is NOT beyond the 6AL, since the tach signal comes from the 6AL internal trigger signal. So it is power, ground, the distributor, the 6AL, or a wire between the 6AL and the distributor.

If you have something less than 7000-7500 RPM and 700 HP, the OEM ignition is actually a much more reliable and better choice. The 6AL is too big for anything driven on the street regularly. It will erode the plug tips, the distributor cap contacts, and the rotor. It is bigger than needed for almost all race applications. I'm at 1200 HP and 8K RPM and only use a small CD ignition box. I used OEM parts (with a MSD coil) up to 1000 HP and 25 psi boost.


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post #4 of 6 Old 09-18-2016, 12:52 PM
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yea TomR, I forgot to mention the dist housing

if you painted the block, you could have a poor dist ground, and/or improper block to body ground.

voltage drop test with the block loaded with current should reveal that.

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #5 of 6 Old 09-21-2016, 08:12 PM Thread Starter
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Thanks guys, I haven't had a chance to work on it yet. Gonna try to get on it tomorrow night, I'll report back on it!

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post #6 of 6 Old 09-24-2016, 10:09 AM Thread Starter
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Turns out it was the MSD 6AL box...

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