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Join Date: Nov 2007
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erratic rev counter,boost gauge/930

any ideas what could be causing my rev counter/boost gauge to give erratic readings. The car runs fine and the fault is intermittent, both needles will flick from
one side to the other, i think there is possibly some kind of voltage stabilizer on the
gauge that needs replacing. Any ideas would be helpful before i send it off for repair, cheers Matt..
Old 02-02-2008, 01:02 PM
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Hey Matt, What year is your car? Any mods to ignition system? I would pull the tach out and check the push on connectors that plug into the back of the guage. Pay particular attention to the brown wire. It sounds like hopefully it's a loose power or ground connector on the back of the tach. It may help to remove the speedometer and only push the tach about halfway out cause it's a pain otherwise. You may can get back there this way perhaps with a small mirror to help you see what your wiggling. Good luck, let us know what you see
Old 02-02-2008, 03:06 PM
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The common reason for this is that your alternator is going wrong (regulator). Try doing a voltage check at the battery to make sure you are not frying your battery. You must have under 14V at high RPM. 13.8V seems to ring a bell to me.
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Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 02-02-2008, 03:32 PM
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Good call nate-dogg, Many, many internal voltage regulators have died. Seems to be worse on 86 and later models for some reason. An easy way to tell if it's overcharging is to use your power windows, headlights, or a/c blower when the tach messes up. If the voltage is too high these will all seem to work REALLY good. Then sometimes they unstick and everything slows down, this usually gets people's attention more than anything in that case. I can't say I've seen it mess with the tach but it certainly makes sense that it could...Good luck
Old 02-02-2008, 04:57 PM
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Can't say about the boost gauage - I have a mechaniclal clock type, but another electrical fault which caused my tach to spike was the setting on the air plate at idle - if the plate is not steady, it switches the fuel relays on/off/on/off.... - this circuit is also wired to the tacho it seems - and the WUR. If you check the volts at the WUR plug and get a steady 12-13, then you have another problem.
If you gets less than 12, and erratic - this could be the problem.
Alan
Old 02-02-2008, 07:58 PM
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Voltage regulator or battery going bad. Not biggy...
Old 02-02-2008, 08:36 PM
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Macht Schnell
 
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Hello,
I've had this problem two times.

1st time, it was the alternator and pretty quickly stranded me. The battery was dead. New Alternator, issue gone.

2nd time, it was a Brown Ground wire at the shroud I had left loose.

Les
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Old 02-04-2008, 09:00 PM
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