Charging Problem

[Robert Jelen]

That's peculiar. Could there be a short or something in the vehicle pulling the voltage down? Or is the belt tension perhaps cocking the pulley just enough to cause an issue?

I think the next thing I'd try is disconnecting the main charge (+) cable from the alternator to isolate it while checking output.

Hey all, I've got a problem. Recently my volt gauge would drop to 11.5 and jump up to its usual 14.4+ area. It kept doing this until finally the needle spent more time on the left side of the gauge. I finally took my alternator in and the brushes were nearly gone so they were replaced and the alternator tested fine @ 14.5+v @ 120a load. The short of the story is that this kept happening. The alt tested good on the bench but as soon as it was installed, the voltage hovers around 12v. I even took it to AutoZone and they tested it twice and it passed all three times. So for whatever reason, once it's installed in my truck, it doesn't want to charge . I even bought a new battery, but the same thing happens. I've cleaned the mounting points of the alternator and the alternator bracket and I've checked all three major grounds and they are all checking out good. The PCM has been tuned out, so the brown wire is only connected to the indicator light. I even connected the jumper cables from the alternators log directly to the battery and from the case directly to the battery and I still have the low-voltage problem. What am I missing?

I had this somewhat same issue. I found it to be the fuel pump was drawing to much amps and causing my voltage to drop. Put the fuel pump on a relay Circuit and the problem went away. I have a 94 suburban with a L96 6.0L

 

[Eveready]

I think the clue here may be in the fact that the problem started slowly and got worse over time . To me that sounds like an internal break in a wire somewhere. It would read proper voltage but if it is down to a strand or two it would be incapable of carrying the full load. I would parallel those jumpers and see if the problem goes away . The fuel pump as Robert suggested could be an issue if it is slowly going bad and drawing more current. Putting a direct line (or relay) on it would eliminate it as a suspect.

Somewhere there is a wire that has gone south over time and is almost but not quite broken. Please post when you find it. There are way too many threads that pose a problem but never finish with a solution. (and I don't mean the ones with a rag in the gas tank! )

 

[thevishnu]

Ah ironic. Mine only does this when wet out (even with a new alt i replaced last week). Going to inspect my grounds in the morning. (89 GMC k1500 with an old tbi 305).

Sent from my SM-G930V using Tapatalk

 

[Ken K]

I am missing some info on this topic. If any alternator has low output, a voltage drop test from B+ to terminal on the alt. running would be first. Also test grounds for clean, unpainted and use "Star" washers to help connections. If this is n "LS" swap, the alternator can be the 4 wire AD244. It is one of the best alternators on the market. Go the alternatorman.com to identify which alternator you have. They sell a voltage regulator for 1 wire operation. A 460 ohms resistor should be installed in series to ignition B+ pink, or in parallel with the 194 dash bulb. This is done to keep the alternator working if the bulb burn out. In parallel, the lowest resistance is the reading...both bulb & resistor are current limiting devices allowing 0.25 amps thru them. The OEM 4 wire uses 6 different regulators...GM uses 26+ regulators depending on year, make & model. That why they don't sell them.
As for slipping belt, i have a front alternator bearing lock up on a 2.8L GM V6 and engine would not crank over until belt was removed. Alternatorman.com has up-graded diodes, plate, bolt and regulator with a set point of 14.2 volt after 3 seconds of start up. LS alternators receive duty cycle signal from BCM, Charge lamp signal and 7.2 volts for supplemental brake booster vacuum pump on signal. Complicated, you bet your sweet Betty Boop! Which one do you have?

 

[JLG88]

Swap in the AD244 145amp alternator. I was running a new factory 105amp alternator and the flexalite fans along with ac lights and radio would drain the output of the alternator. Also look at adding the sensing wire in the 4 pin plug of the alternator.

I swapped in this alternator and no more problems. The ad244 fits in the 96+ brackets and the 88-98 brackets with slight modifications I can get pics of both setups if you need it.