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Topic Review (Newest First)
04-02-2015 08:04 AM
zuma6195 I've been following your post because my 3.0L ford is doing the same thing. So, did replacing the alternator and coil pack solved the rough idling problem ?
12-28-2014 09:12 PM
amc49 FYI to all as Milton seems to say...................if the battery is KNOWN GOOD (loadtest!!) and FULLY CHARGED (your charging of it and professing it to be full without measurement is worthless) the car will run PERFECTLY with a bad alt unless alt has faulted in such a way to provide some kind of direct power bleed down like a short. You'll know if that by itself and the sparks. Other than that scenario the car should run fine with just a good well charged battery.....idle issues at that time point to other things.

I call a good battery one that after sitting overnight after charging still shows 12.5-12.8 volts.
12-28-2014 01:32 PM
Mandroid I think you need to seriously look into the alien space ship theory...

But really, what Milton said is correct. However, the alternator is a common failure part on these cars. But don't go replacing things without testing first. Do you have a multimeter?
12-28-2014 12:54 PM
bad alternator causing rough idle ?

Alternator, or battery or wiring or connections or any combination. Go over all wiring and connections. Then have the battery charged and then load tested. Then have the alternator tested.
12-28-2014 02:47 AM
MarkTheShark My vehicle runs fine until I turn on the headlights or flash high beams which both cause engine to shake, cut out, and cause gauges to go crazy like an alien space ship is nearby. Could my issue be an alternator?
02-14-2013 03:39 PM
SVTF 03 I did a test with 3 local well known auto part store chains with my alternator. Had it tested at the first store and it was good, then took it to another store of the same name and it failed. Then took it to the other 2 different chains and said it was good. Watched these noobs try and hook it up and I had to tell them how to do so and how to even mount it in the machine they had. I hate taking my stuff to people that are ignorant. Ended up doing my own test with a voltmeter and determined it was bad after all. The power post was shorted to the case. So the positive cable post on the alternator was acting as a ground. I actually ended up finding all of this out after overnighting a 230amp alt to go in my SVTF (I always am looking for the best bang for my buck). It worked for 2 minutes and died (covered under warranty). That is when I did all the testing. Now I'm not sure why the 230amp alt died. But I did notice on the all-in-one harness (Negative, Positive, and Starter Cable) that it has a 175amp inline fuse in the factory wiring. I have a brand new harness with the same rated fuse. My guess is the factory wiring can't handle the 230amp alternator or vise-versa. But that's just a guess. But the original bad alternator was definitely the culprit of my engine running issues.

I have yet to do a Big 3 upgrade. But from what I've read it would be a definite improvement. My car ended up dying on my way home from work one day with no real indication of any issues. I had replaced the coil and wires before all this happened, just as preventive maintenance and it just needed a tune-up.

You should have 13+ volts when the alternator is charging. Just put a voltmeter to the battery when the car is not running. You should see 11.5-12v depending on the battery and it's charge. Start the car. The voltmeter should show 13+ - 14.5v. If it's not charging, check the 3 prong connector. It's been said these go bad. Mine was in great shape. I remember talking with Tom (Focus-Power)(Turbo Tom) and he had mentioned the RPM in which the alternator can start charging can be changed IIRC.
02-13-2013 05:02 PM
beatmaniac1 So we changed the alternator today but we also found that the problem was a bad coilpack ( seems like they happened to both fail at the same time ), it's gonna get repaired tomorow so i'll finally have my car back and runing again ...But its going to cost a small fortune it sucks that I had to go to a garage ...
02-12-2013 12:54 PM
beatmaniac1 I checked the voltage with the in-dash test mode, which I believe is pretty reliable (is it ? ) . The lcd wouldnt display 12 v till I hit 3000 rpm and the battery is less than 6 months old so I figured the problem had to be the alt. I havent run the car since the problem appeared. Its gonna get repaired tomorrow morning probably so i'll know for sure. But thanks for the answers, i'll let you know if the alternator was guilty of the bad running of the car

thanks !
02-11-2013 11:43 PM
bd8134 If you think you have a bad alternator you should either get it checked out for sure or replace it. Autozone or Advance Automotive do this for free. It is a more comprehensive test with it removed.
Yes low voltage can cause a bad idle and you may end up breaking other parts if you drive it like that.
02-11-2013 12:41 PM
LittleRedSVT My alternator failed a diagnostic test and I also have rough idle... I cleaned by IAC valve, didn't do anything.

Help would be appreciated.
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