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Join Date: Feb 2006
Location: Montreal, Canada
Posts: 229
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1981 SC Tachometer going wild ???
Started yesterday , Was running smoothly on the highway when
I saw the tach starting acting funny going to 7000 rpm`s and back down to 0, It did this intermitently until I got home and shut the engine off. I also noticed that when applying the trottle it would jump back & forth ??? I also could ear the gears in the tach spinning like crazy ? Anyone knows what is going on .......... Is My tach going south ? Francois |
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05-05-2009, 08:12 AM
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Join Date: Oct 2006
Location: MYR S.C.
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put a multimeter on the battery with the car running and check the volts. should be around 14v
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86 930 94kmiles [_  _] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD88 BMW 325is 200K+ SOLD 03 BMW 330CI 220K:: [_ _] RUNNING: [__] NOT RUNNING:01 suburban 330K:: [_ _] RUNNING: [__] NOT RUNNING:RACE CAR:: sold |
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05-05-2009, 08:22 AM
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Location: Montreal, Canada
Posts: 229
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tach
Would that have something to do with the charging system ?
Francois |
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05-05-2009, 08:26 AM
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Join Date: Mar 2001
Location: Marysville Wa.
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Quote:
usually does. there are exceptions. when you're almost out of battery voltage to run the car (fuel pump), the radio quits and the tach floats, you better start looking for a place to land.
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https://www.instagram.com/johnwalker8704 8009 103rd pl ne Marysville Wa 98270 206 637 4071 Last edited by john walker's workshop; 05-05-2009 at 05:18 PM.. |
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05-05-2009, 08:33 AM
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Free minder
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This happens when the voltage in the system becomes too low. I used to have this issue and solved it by cleaning my battery posts.
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1978 SC Targa, DC15 cams, 9.3:1 cr, backdated heat, sport exhaust https://1978sctarga.car.blog/ 2014 Cayenne platinum edition 2008 Benz C300 (wife’s) 2010 Honda Civic LX (daughter’s) |
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05-05-2009, 08:41 AM
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I had the exact same issue and I replaced the alternator and that solved it. If I remember right, if you have the alternator with teh separate voltage regulator you ban start there, otherwise try the alternator. In my case I ran it until the battery died, this gave me another sympton it was the alternator. Good luck!
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Vance '83 SC Cabriolet - The "Matrix" '73 914 - "Spicy Mustard" - SOLD |
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05-05-2009, 08:49 AM
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Wildman Emeritus
Join Date: Feb 2003
Location: Chitown Burbs
Posts: 1,875
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Could be as simple as a loose battery cable clamp. Don't ask me how I know.
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Mike Andrew 1980 SCWDP 2024 Suby Forester 2018 BMW X1- Wife's 2000 Boxter - Sold |
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05-05-2009, 08:56 AM
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azporsche911.com
Join Date: Nov 2005
Location: Goodyear, Arizona
Posts: 284
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My car did this same problem of the tack needle bouncing along with my head lights dimming intermittently at night. Turned out to be the voltage regulator had gone bad.
But find out if you have an internal or external regulator, my car at one point had been converted to an internal but the external reg was left in place. i bought the external reg and it didnt fix the problem, so i removed the alternator and discovered it was converted. after i took it to a place here in town to get rebuilt (paid about $40), all was good. -Jeff
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Jeff Hoffman (Son) Tom Hoffman (Father) 79 911sc ROW guards red coupe father son project. Last edited by Hoffmanmotors; 05-05-2009 at 09:10 AM.. |
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05-05-2009, 09:08 AM
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Join Date: Nov 2003
Location: BABYLON,N.Y.
Posts: 1,048
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Tach
2nd the bad voltage regulator
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05-05-2009, 09:36 AM
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RETIRED
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Mine was the precursor to the alternator goes tits up....
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1983/3.6, backdate to long hood 2012 ML350 3.0 Turbo Diesel |
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05-05-2009, 12:41 PM
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Just happened to me last week too. It then led to a dead battery. Turns out it was the alternator.
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05-05-2009, 12:59 PM
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Happend to me too. Mine was an alarm wire (siren) that had slipped out of the harness, rubbed off the insulation, and was intermittely grounding out against the frame. A small bit of electrical tape and re-routing of the wire fixed the problem.
Check for loose connections or rubbed wires. Past that its either the alternator or the regulator.
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Don't Lift... Don't Lift... Don't Lift  '75 Targa in "Arrest Me" Red, 3.0SC ('79) engine, Bilsteins, Turbo Tie-rods, SSIs into 2-1 M&K muffler... and looking for my next upgrade. |
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05-05-2009, 01:23 PM
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Join Date: May 2009
Location: Cedar Hill, TX
Posts: 16
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Check the plug connection on the bottom of your CD (ignition) unit, sometimes get knocked a bit when changing your fuel filter
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1981 SC Targa Euro - Minerva Blue 2003 Audi A4 1.4T 1999 Audi A4 1.4T - Hers |
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05-05-2009, 04:01 PM
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Quote:
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Aaron '81 911SC RoW Targa |
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05-05-2009, 05:50 PM
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Location: Montreal, Canada
Posts: 229
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wild tach
gees , thanks for all the inputs guys. I will have a look asap and try to
pin the problem. Great forum Will keep you posted Francois |
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05-06-2009, 08:11 AM
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Join Date: Dec 2006
Posts: 356
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A whole collection of electrical gremlins were eliminated when my faulty alternator was relpaced..... including the bouncing tach.
Good luck.
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______________________________ 1989 Carrera Coupe (Black / Linen) 1981 911SC Targa (Black / Chocolate) |
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05-06-2009, 04:25 PM
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Join Date: Mar 2008
Location: Thousand Oaks, California
Posts: 367
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Alternator/voltage regulator/battery/cables. One or all going Tango Uniform.
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05-07-2009, 09:04 PM
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Hi
Ive got the same issue and .... Would this wire have anything to do with it. It is hanging down from under the dash. It must be live because I tucked it under the dash and then the lights, wipers and other electrical stuff quit working. Any idea what it is. I 
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05-08-2009, 09:20 PM
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Join Date: Feb 2007
Location: Tustin. CA
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BROWN is GROUND. General rule with Porsche. Check your voltage output from your alternator. check battery voltage with car off first...say 12.8 V. Then check it with car idling...should be 13.8-14.2 V. If it is higher your regulator may be bad.
The wire in your pic looks like it has a resistor in line. That may be the wire for the instrument with your alternator warning light in it. Some require the resistor to excite the alternator. Does your alternator light work when you turn your key to accesory position? Cooper
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Cooper's Classy Car Care Providing Clear Bra installation, Paint touch-up, Detailing PCA/OCR since 1997 '81 911SC, '95 993 Tip. Project 'Euro spec' '70 914-4 w/2.0 & side shifter |
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05-08-2009, 09:41 PM
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Which light is the alternator light?
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1978 911sc Targa Sold 2001 996 Cab Sold 2006 Cayenne S Silver Wifes Car for sale 2011 Jeep Wrangler Silver for sale 2010 Toyota Prius Black for sale 2016 BMW 328D wagon |
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05-08-2009, 09:58 PM
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1983 Porsche 911 SC Cabriolet 3.0
Da cab
chocolatelab
