What a bad alternator can do to you S197! - MustangForums.com

Florida Regional Chapter Chapter President: ShakenRoush05

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Old 02-28-2012, 08:34 PM   #1
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Default What a bad alternator can do to you S197!

About 8 months ago I started to notice a drop in performance in my 05 Roush. I use my car as a daily driver and at the time had about 103,000 miles. The first sign was coding on post O2 sensors. So I changed them all, with the problem subsiding for a short period of time and resurfacing again. Then without warning my gauges started doing some weird things. For example, the temperature gauge would signal a low temperature reading followed by my tach being stuck at 2000 RPM at idle. The engine was idling properly but the tach was out of sync and starting out at 2000 RPM.

Finally, the defining moment; Cam sensor fault. So I started doing some research and found out that a diode in the alternator (when failing) allows for ripple currents (electronic garbage to migrate throughout the system and cause a cam sensor fault. It is almost unheard of that the cam or cam sensor is at fault. So I changed out the alternator,re-flashed my car, assuming that there would be remnant garbage in the system memory.
Immediately it felt like I had 50 more HP and all of my issues are a distant memory, power, performance and fuel economy are way up. I am lov'in my car again.
Who woulda thunk it...

Last edited by ShakenRoush05; 02-28-2012 at 08:36 PM.
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Old 02-28-2012, 10:17 PM   #2
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Hey glad you found out what it was!
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Old 03-07-2012, 06:27 AM   #3
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I actually posted this story for everyone that might be having some weird things going on with their cars and might just be the same problem!
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Old 03-17-2012, 08:21 PM   #4
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I'm considering changing mine out just because of the known failures. My car only has 40k miles too.
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Old 05-20-2012, 09:13 AM   #5
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Interesting posts. "Ripple" basically is a remnant of the rectifying process... i.e., when you convert A/C (as output by the alternator) to D/C, the type of electricity our cars live on. Absolutely caused by a faulty diode.... diodes being the "Check Valve" in the electonics world. So ripple is a fluctuation in the current. Ironically, if we had actual GENERATORS as apposed to ALTERNATORS, it would not be an issue.

LOL... last car I owned that actually had a "Gennie" was a 1960 Oldsmobile back in 1979.
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Old 11-23-2014, 08:31 PM   #6
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Interesting! I have that issue w/my '05, Cam Position Switch & CPS intermittent circuit. I have replaced that same unit (bank 1 - passenger side) 3 times and the problem goes away for about 2-3 months, then comes back again. And when it does come back I get a bunch of dead spots during acceleration or at a constant speed. I also not a decrease in mileage. The only thing that I've done to 'cure' it is to delete the codes and it runs fine for about 3-4 weeks. This has been going on for almost 4 years now and I have taken her into a few Ford dealers for diagnostics. They just tell me that the CPS is bad and can't find any other issues. My '05 is also a daily w/~86K on her.

Thanks for this heads up on a possible fix!
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Old 06-08-2015, 04:37 PM   #7
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I wonder if this is what is causing my hard start issue on my InTech swap. It NEVER starts on the first crank but on the 2nd or 3rd crank it will start.

I know my alternator is weak so I'm wondering if that is sending these ripple currents / garbage signals to my cam or crank sensor.
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