Hey guys, haven't been on in a while, son's truck running fine. Since his Temperature gauge is not/has not worked since we bought it, I bought him a scan gauge II to use. He calls it his redneck racepac .

I drove the truck for a few weeks back and forth to work, and played with the Scan Gauge while sitting in traffic. The voltage reading, to me, seems low. As high as 14.1 to 14.2 (right after start up) down to 13.5 while idling, hot, in traffic. Driving 60+ mph down the road, reads 13.8 to 14.0. As typical teenagers do, he has some sort of high powered amp installed (500w x 4). Had it installed professionally, local shop in business for 30+ years.

Do I need to think about a new or higher rated Alternator? Thanks.

 

Try an accurate DVM connected at battery posts first, scan gauges have been noted to have something less than precision voltage calibration, or voltage readings at scan port are anyway.

 

Here's how I resolved the low voltage issue on my 2002 Navigator (can't say for sure if it is your issue, but its worth checking):


https://www.ford-trucks.com/forums/1...or-issues.html

 

Charge voltages are temperature dependent, too.

Higher in cold weather, lower in hot weather. Assuming the scan gauge voltages are even accurate, they don't look too out of line. Idle alternator voltage is one thing, also measure volts at say ~2500 RPM with headlights on, heater blower on HI; notice the charge voltage will sag, but should still maintain around 14 volts.

The resting open circuit voltage of a battery is about 12.8, the "float" about 13.2, so remember at a glance anything below that means battery is discharging. The alternator provides all the voltage for everything, the battery is just along for the ride.

Check resting battery voltage. Open circuit voltage of a fully charged modern "maintenance free" battery (surface charge removed) is 12.84 volts. This is a very accurate test of battery health if done correctly.

As a quick troubleshoot on alternator charge voltage connect a heavy jumper direct from battery negative terminal to clean unpainted spot on alternator case. Observe if charge voltage increases at idle and high RPM under load as before. Another thing to look at is how well the battery performs under a real world load test - like cranking the engine. I picked up one of these for about ten bucks and they and the cigar lighter/accessory port seems to show accurate state of battery voltage and charge rate. Cheaper than a scan gauge, and those aren't useful on the older iron anyway. Let us know what you find.

 

I would add one comment on the charge system.
The voltage regulator has a reference built in that is the control point for everything that goes on whether it be voltage drop from , poor battery condition, bad cables, grounds etc.
Specifically, the difference between system voltage it detects and the reference determines the alternator output into whatever load/drop is present at any given time.
If the regulator becomes faulty or unstable for any reason, the results of alternator output is all over the place.
Good luck..

 

Those voltages are within normal limits.

 

Not sure where you are located, but here in Central New York State the temps have been dipping into the 20's late afternoon and evenings. With my alternator grounded with my home made cable at these cooler temps it will read 14.7/14.8 volts at start up, idle at 14.0/14.1 volts when the air ride compressor kicks on, and will go down the road reading 14.3/14.4 volts. (Before adding the extra alternator ground cable the voltage monitor was most always reading 13.x volts)


I think your voltages are a bit on the low side. Don't know if it is wiring issues or load or perhaps your alternator drops off as it heats up.


Just my $.02.

 

Lets get into some more about how the charge system works.
The regulator has the reference fixed at some voltage near 14 volts +/-some tolerance which the system operates to.
When cranking, the load on the battery discharges it some amount depending on temperature, oil viscosity, transmission fluid viscosity in the converter and cranking time interval. etc.
After the engine starts and brings the Alternator up to a min speed, the regulator sees the lowered voltage from the battery.
This battery voltage will be below the regulator reference value.
This difference between the two values sets the alternator charge voltage higher than the reference and 'forces' current back into the battery to replace and raise the battery charge level toward the reference value.
So the initial voltage after starting will be upward of 15 volts and tapers down as the battery recovers it's charge in a short time, if the battery is in good condition.
Normal battery full charge and running voltage should be around 14.1 +/- a tenth or so.
Under normal loads the voltage should not change more than a couple tenth because the regulator monitors the total system and keeps the regulation pretty tight in a trouble free system..
Good luck.

 

Remember the scangauge voltage indications are typically different than actual voltages at the battery by a fair amount, sometimes a half volt. Doesn't sound like much but, if this is the case here this is important, because tenths of volts are critical when it comes to batteries.

On the assumption these figures are low the true voltages are probably OK but. If there is a concern, then get known accurate charging voltages at the battery itself, under load, and then compare with charging voltages after a heavy jumper is connected from battery to alternator case. Charging systems do not like high resistance in the circuit, it "fools" the voltage regulator, testing will sniff that out.

 

WOW, thanks for all the help guys . Well, after I posted, I got called in to work for a couple of graveyard shifts and could not get out and work on it. I did read the responses, so today I went out and hooked up a jumper from the alternator frame to the negative post as advised. I am in Texas (Houston Area) so I am not seeing the temps some of you guys are (cold). BBAAMM, 14.0 to 14.2 driving down the road, a/c on (for test purposes), and my son's stereo on . Start up I have seen as high as 14.3, but mostly 14.0 to 14.1. All of these are via the scan gauge. I may increase the size of the jumper wire as I am not comfortable with the one I put on. It was simply something I found in the garage. Thanks again!!!

 

The jumper is just for test purposes not a permanent fix.

Your test indicates there is excessive resistance (corrosion most likely, sometimes paint) in the ground cables and connections, the alternator ground itself to the mount brackets/block itself. The positive side wiring is also subject to the same thing.

It pays to ensure clean, tight electrical connections in the charging system.

 

Why not have the jumper as a permanent fix?

 

Suppose you could if it was heavy enough but that's not good practice, consider too the voltage drop there means there are issues elsewhere - the headlights and ignition are being starved for voltage as well, also accessories like the heater motor, the long run all the way back to brake lights etc.

The proper thing to do here then, is clean everything up with new battery cables and ground straps (important) at frame, block, and firewall, and also paying particular attention to the connection made by the alternator to engine block at mounting boss, mounting hardware etc. Sometimes this is the main negative battery terminal ground point on an engine as well. This is always the issue with older trucks, steel just isn't that suitable for electrical.