LUVTruck.com

Well I recently had a problem with my 79' LUV where what would happen was the GEN light would illuminate and 10 seconds later the engine dies. I start it back up and it dies another 10 seconds later. I ended up replacing my voltage regulator and it's working fine. Just curious though when I check my voltage at the battery while running it is only reading like 12.45 volts. It should be around 13.4 volts right? I took my alternator in to get tested and they said it was fine. I'm not having a problem with the battery not charging enough now, but I'm afraid if I draw more current from the alternator for other things like my stereo or ac inverter and other things that the battery may not get a charge at all. Is this normal? Is there anything I can do? Thanks everyone.

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If your charging system is not charging it will shut down your fuel pump. I do agree that you should see more voltage then you are. Mine charges at 14.4 but it does not have a stock alt either.

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Certified pilots, looking down on people since 1903.

I do have a stock alternator. Is there an aftermarket one you suggest? And will it fit on the stock bracket?

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Is that your charging voltage at idle or with engine revved up some? Makes a difference. The mechanical voltage regulators are adjustable for output voltage.

That's at idle. It gets to 13 @ around 3500RPM.

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Adjust to 14.2V, fully charged battery, 2500 RPM, warmed up and stabalized.
If the battery is not fully charged it will read low so do this first.

How do I adjust it?

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A bit complicated but I'll take a stab at it.
Battery charged up, right?
Warm up the engine, remove the regulator cover, carefull not to short anything with the metal cover.
With the engine running about 2000rpm connect voltmeter to battery to monitor voltage. Inside there will be two coils, one is a relay for the fuel pump circuit, the other will have a small spring down the side of it. Pushing lightly against this spring (making it pull tighter) will cause the voltage to increase. Some will have a philips screw at the base of the spring mount to adjust, others just have a tab to bend down a bit and make the spring tighter. Careful, it only takes a very slight amout to adjust. Also careful not to short anything out. It takes "finese". Putting the cover back on may change the setting a bit, you may have to compensate.
All this is assuming you have a mechanical regulator. A solid state one and you are out of luck, just have to replace again.

Thanks for the information, but just curious how my regulator will put out more voltage to the battery if my alternator isn't creating that much in the first place?

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Alternator output is controlled by voltage regulator which senses voltage in field wiring. Field wiring is the main wiring harness circuit in the truck, so any load drawn from field wiring tells regulator that more voltage is needed. Alternator's output is continuous, like 15 volts, and regulator either applies that voltage to battery or shunts it.

You can 'fuul field' and alternator to cause it to put out its maximum voltage unregulated by the regulator, but I don't know how that's done on the Isuzu system.

Thank you for the information. It has greatly helped me.

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Like JimmieD said, an alternator puts out whatever voltage it is told to by it's regulator.
On a stock Luv system you "full field" it by applying 12V to the field terminal of the alternator. This will cause full output of the particular alternator, in this case 35 amp. Only used for a quick test to eliminate alternator versus regulator problem. Only for a short duration or things will fry!