Please Verify This Logic Re Charging Failure

[VinDiesel]

Took '98 2500 6.5 4L80E truck out tonight to test HB. Noticed voltmeter going d-o-w-n d-o-w-n. Could not make it home as truck died - I assume from no electricity (HELP, ARNIE!). First logic question: assume bad alternator is culprit as batts are only Aug. this year => no charging. Is there anything else that could get in the way of what appears to be a no-charge scenario? Second logic question: would a failing alternator cause transmission oddities, i.e. not shifting properly (acted like it was in another gear, maybe 3rd) and no turbo? (Other problems like blinkers failing, lights dimming would indeed be from no juice.) I have to decide whether to tow home and try to fix or to *dealer* so any help will be greatly appreciated.

[charliepeterson]

These trucks NEED alot of power from the batteries/alternator. If the batts. are new and you noticed the battery or charging symble on the dashboard I'd guess the alternator quit or the serpentine belt broke.
If the belt broke take a good look at the A/C compressor for locking up.

[VinDiesel]

Thanks charliepeterson for the review. Belt looks OK so alternator seems prime suspect; I sure hope so. Have had truck for all of 2 weeks = haven't had chance to get manuals. Will check alternator setup tomorrow in daylight but in the meantime is there anything special in the way of technique or tools to be aware of when removing the alternator since I am now thinking of a tow job home rather than to dealer? (BTW, I try to find answers via Search before posting here.)

[rjschoolcraft]

The alternator is easy to change...no special tools needed.

[moondoggie]

Good Day!

Never assume anything, especially when electricity is involved. I would NOT throw an alternator at this problem until looking at the following:

</font>[list] Make sure all battery connections are perfect - anything less will give trouble.</font> Make sure battery ground connections (probably at intake manifold) are perfect. I like to purchase external tooth lockwashers & put them under any grounded wire/cable connection, between the tab on the end of the wire/cable & the engine part it's grounded to.</font> Start the truck & measure battery voltage. Then turn the HVAC blower on high & the rear window defroster or another big load. You should see &gt; 14V at the battery in either case. If it's a little lower with the loads turned on, have an assistant raise rpm to ≈ 1000 - it should go over 14V. My trucks all seem to run ≈ 14.5V at 70

[m-keith]

Changing an alternator on these trucks is WAY too easy to have someone else do it. Once you have it out, you can have an electric shop bench test it. Just make sure you note the belt's routing, & I'd go with a new belt regardless of what the current one look like.

When mine went out, the tell-tale sign (in addition to the battery light) that it had failed was that the tach stopped working. The 6.5 gets its tach signal from the alternator.

[VinDiesel]

Thanks for the help here but I think something far more serious than alternator is wrong. Charged the batteries and thought to start Burban up and move the front end back a little (the tow left it hanging out in the driveway). Symptoms: voltmeter acts like the batts. are dead (voltmeter says 13.5; instr. panel says dead), no start whatsoever, or click or anything; like there is absolutely no juice to the starter; doors lock/unlock continously; continual clicking sound from instr. panel area, no instr. panel lights at all, i.e. no batt. symbol, no SES even, no air bag, etc. etc. Suspect clicking sound is attempt by whatever electronic unit does things to "cycle" through the startup process. I really need some guidance on what I might look at.

[VinDiesel]

More clues about how wrong I was re alternator. Continual rapid tick-tick-ticking sound even w/ ignition OFF. Had to disconnect batteries to kill it. Also, when ignition in off position, oil gauge has pressure reading while all others are down.

[GMCfourX4]

Start with the electrical connections. Check the grounds on both the battery and engine or frame ends. If you have a meter, make sure each battery (when disconnected) reads at least 11-13V across the terminals. If you have corrosion on any of the connections, clean them with a wire brush and put a little dielectric grease on them. Let us know how it turns out.

-Chris

[Phil Holmen]

There should be a fusible link somewhere between the alternator and the battery, check it befroe suspecting the alternator. I have also seen where the alternator was actually drawing power.

[tom.mcinerney]

Above all good suggestions. I'd start/keep with remove & test alternator first- shorted output diode may be culprit. Any good electric shop should be able to get some clues on alternator.
After remove & replace alternator(and secure major battery/ground connections) do still have drain when connect batts? Major power tracks through 'underhood fuse/relay center', then to ignition, light switch, and instrument panel fuse center(left end dashboard, need open door), and relays mounted beneath instrument panel above clutch pedal/park brake.
Sometimes 'tested', even 'new' alternators aren't good enough, but at least it should run and act more normal....

[VinDiesel]

Without belaboring the labor, it appears the problem was the cable linking the batteries causing the car to have only the driver side battery! Fixed that and all seems well. Since this is my first vehicle newer than 1988, I think I've learned that no juice on this baby = no car! Much heartfelt thanks to all the folks who responded to the call for help. There is much good information in those posts that will come in handy again and again. smile.gif

[JohnC]

Originally posted by VinDiesel:
I think I've learned that no juice on this baby = no car! You got that right! The trans shifts electrically. The throttle is electric (as is the injection pump) to say nothing of the security system, door locks, etc. They act possessed when the juice is not flowing right...