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Old 09-03-2012, 01:28 PM
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Speedometer drop w/electrical load issue?

So, yesterday I noticed that when I step on the the brake, my speedometer needle spikes down in a low drop, then bounces back up to the speed I'm actually going. Then I tried turning on the headlights, and the speedometer did the same thing. It happened for other equipment I tried that put an electrical load on the system too. The cruise control, which I rarely use, wouldn't work either. (The night before I did drive through a soaking torrential downpour, so maybe it could be some kind of short. I'm more concerned that it could be an indicator of some larger problem.) After letting the car sit for several hours, I drove it home and didn't get any more erratic speedometer readings, but when I tried the cruise control, it still didn't work. Has anyone else had this happen? Is it likely to be a symptom of something more serious?
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Old 09-03-2012, 06:23 PM
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Re: Speedometer drop w/electrical load issue?

Battery or alternator or both are on their way out. A competent autozone or advanced will check them both for you. You should also check your crank pulley to be sure it's not separating.
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Old 09-04-2012, 05:27 PM
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Re: Speedometer drop w/electrical load issue?

Thanks Dave. I used a multimeter, and the battery output was 12.4 volts and the alternator output was 14.6. I didn't drive the car or let it run before the test though. Now I went back and tested the alternator output again, this time turning on other equipment to increase the load with the engine idling. With one or 2 on, the voltage drops down to the 13.X range. With everything possible on, it drops down to the low 12.X range.

I also tried wiggling the crank pulley perpendicular to the rotation direction, and it didn't have any play. But maybe the belts are keeping it snug?

The idle isn't constantly smooth, though. It occasionally sort of shudders (short but gradual increase and decrease in vibration and noise), and a small voltage drops seems to be associated with that.

I tried getting an ECU code reading once it started doing that. The "check engine" light did one long blink followed by 2 fast blinks, and then kept repeating that pattern. Is that supposed to be interpreted as a "3" or a "12"?
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Old 09-04-2012, 06:55 PM
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Re: Speedometer drop w/electrical load issue?

That's a "12".

For the crank pulley, use a paint pen or some white-out to make a stripe across all three layers. Occasionally check to see if the line is still in one piece. I once had one that would only slip when underhood temps got higher (hot sunny day, slow moving traffic, AC on).
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Old 09-06-2012, 09:09 AM
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Re: Speedometer drop w/electrical load issue?

Great suggestion! I really wasn't sure what you meant by "separating" - or that there were 3 layers - until this post. I put some white-out on yesterday. We'll see what happens.
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