Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2491411
05/03/18 12:24 PM
05/03/18 12:24 PM
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Joined: Dec 2005
Posts: 11,551 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,551
Fulton County, PA
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Sounds like pick up, although they usually either work or they don't. Swap in a known good box would be the second choice. Look at the wiring for damage or shorts.
If the results don't match the theory, change the theory.
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2491516
05/03/18 03:03 PM
05/03/18 03:03 PM
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Joined: Jan 2003
Posts: 13,362 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,362
Marion, South Carolina [><]
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Hopefully you aren't still running the factory ammeter/ampmeter in the car? If so, it could be going bad b/c when mine went, that's how it started...right before it burned up the wiring harness.
Also seen a bad tach cause weird misfiring issues. Unplug it and try.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Tach goes crazy and engine starts missing
[Re: MR_P_BODY]
#2491559
05/03/18 04:16 PM
05/03/18 04:16 PM
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Joined: Jan 2003
Posts: 4,717 Moved to N.E. Tennessee
GomangoCuda
master
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master
Joined: Jan 2003
Posts: 4,717
Moved to N.E. Tennessee
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When this happened to me my first thought was bad tach. Disconnected it at the coil and the ignition was back to normal. I was ready to pull the trigger on a new tach when it occurred to me that there was also a rev limiter connected to the same wire. Unhooked it and hooked The tach back up. Yeah it was the rev limiter.
Last edited by GomangoCuda; 05/03/18 04:16 PM.
In theory, there is no difference between theory and practice. In practice, there is.
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2491822
05/04/18 07:25 AM
05/04/18 07:25 AM
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Joined: Feb 2003
Posts: 2,810 Sobieski Wi
bee1971
master
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master
Joined: Feb 2003
Posts: 2,810
Sobieski Wi
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Just posted this a few days ago on this thread https://board.moparts.org/ubbthreads/ubbt...tml#Post2233534Sounds like a lot of MSD Coils are failing lately from the research I did the last few days Had my new 432 Stroker on the road the other day for the first time in over a year Cruising on the highway after about a hour the engine started missing at high rpms Turned around and headed home , where it started getting worse even at lower cruise What I first noticed was the tachometer needle was bouncing all over the place , had a mind of its own Went to touch the MSD 8202 Red Coil checking the tach wire , was super super hot Just swapped in a old Mopar Resto coil that I had laying around along with a .8 resistor Ran it for a few hours problem solved This MSD 8202 Coil I had for about 5 years , ran fine with MP Chrome ECU , MP Distributor prior First day with the new motor , had me wondering now what - The Tach issue was the only thing that pointed me directly to the coil Anyways , this MSD 8222 Epoxy Coil - Better ? Same ? Is there a better coil in factory location bracket on aluminum intake ? Or is it time for a FBO Upgrade or Rev n nator Upgrade for this new motor Street Use Thanx Scott
1971 Dodge Charger Superbee 2011 Ram Sport 1500 Quad Cab Deep Water Blue Loaded Siberian Huskies
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2492036
05/04/18 03:34 PM
05/04/18 03:34 PM
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Joined: Dec 2005
Posts: 11,551 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,551
Fulton County, PA
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I can see an internal short or failure causing that, if the tach signal is being picked up right at the coil primary terminal and not the port at an MSD box.
If the results don't match the theory, change the theory.
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2492263
05/05/18 01:20 AM
05/05/18 01:20 AM
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Joined: Jun 2005
Posts: 6,257 gulfport, ms, west mi
rowin4
master
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master
Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
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This is what I had happen back in the 80's with my Fiero GT. same symptoms . 1 spark plug wire had a crack and for some reason every once and awhile it would start throwing sparks to the block making a miss and screwing up the tach. Took a while to figure it out but a change of wires did the trick.
it's ok to butt heads, just don't do it with a butthead
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2493027
05/07/18 01:17 AM
05/07/18 01:17 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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10 years is a long time for plug wires.. since it was raining out I would look under the hood in the dark and see if the spark is jumping under there.. but I would start with wires
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Re: Tach goes crazy and engine starts missing
[Re: dirt]
#2493193
05/07/18 02:14 PM
05/07/18 02:14 PM
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Joined: Dec 2005
Posts: 11,551 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,551
Fulton County, PA
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Use a spray bottle with water in it and spray a fine mist on the wires after dark. You'll find out pretty quick what condition the wire insulation is in.
If the results don't match the theory, change the theory.
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