Hello all!

Been lovin' the '04 Excursion 6.0L since I got my engine issues worked out. Pulls like a dream.

I have a question about a charging 'issue'.

Background:
Replaced both batteries when the truck wouldn't start. A couple days later my ABS light came on and the dash lights went dim. Truck wouldn't start. Replaced the alternator which was confirmed bad by Autozone. A couple of days later my battery light faintly flickered for under 20sec and went out...never to happen again. All was OK...I thought.

'Problem':
Truck was in for general maintenance at Ford today (about 3 months after charging system problem). They called to say the alternator was only putting out 11.8V. No way I thought because I've been driving it problem free for a few months.

Took it to Autozone and they showed about 14v and 44amps (110amp alt) at idle. Battery was 12.5 engine off. They questioned whether the amps were low but thought OK since the batteries were near full.

At home I confirmed their voltage readings with my voltmeter (all testing done from battery terminals and reading consistant at each battery), but decided to test under load (lights on, A/C blasting, radio on, etc...). At idle the voltage dropped to about 12.2V. At about 1500RPM the voltage only climbed to 12.4V.

Question:
Is this a possible indicator of an alternator not putting out good voltage/amps under load, or are the readings OK? They seem low under load with engine at 1500RPM, but I might not now any better...

Thanks!
Paul

 

Those readings sound ok. At 12.4v it's still keeping up with the loads you presented, though it's not charging the battery very much. The readings may go higher if the rpms are increased a little bit more.

 

Thank you for the reply.

Any chance that the alternator volts could be OK but the amps not? Alternator amp output is low when battery is full...alternator amp output is high when battery volts drop, right?

Any easy way to check alternator amp output?

Thanks again.

 

Alternator output is directly related to the voltage of the system. The regulator uses the voltage level of the elec system to judge how much output the alternator should have. You are correct, when the voltage of the system drops, the regulator kicks the alternator in more to try to keep the voltage level up.

Cruising along with not much load, the voltage will be around 14.5v. With your load test, I would bet the alternator was near capacity for that rpm, since it was barely able to keep the voltage at battery level.

The only easy way I know to check alt output is to put the alt on a test machine.