Re: big problem with my xfire, please help
Well, it depends.
If the engine is cranking over, but will not fire up, then it is most likely the Crankshaft Position Sensor. Possibly even the Camshaft Position sensor, but those fail on a much less frequent basis.
If the engine never cranks over at all, you just turn the key, and nothing happens, then its typically the Relay Control Module acting up. Just have your friend double check his handy work.
If the car acts weird while driving, then it might be the battery, like what was the original issue in this thread, I believe, or the one that sparked the debate.
As for the debate about alternator issues, one thing no one has mentioned as of yet:
In todays cars, there is logic in the ECM that can tell the alternator to activate an additional set of windings in order to produce more energy to recharge the battery quicker, and also to deactivate those winding, so that the car saves a bit of gasoline, since the engine doesn't have to work as hard to spin the alternator.
Its entirely possible that with a weak battery, the car doesn't have enough stable voltage, and the alternator isn't putting out enough juice to keep the car running reliably when fully warmed up when the ECM powers down the alternator.
BC.