Alternator question

[chadc281]

I've periodically had some weird electrical issues, like the gas guage showing 0 and the windshield wipers not turning on but it's few and far between and usually starts to work fine after turning the engine off then back on. it was suggested to me that i get the alternator checked out so i went to autozone yesterday and they hooked up their checker to the pass side battery pos and neg terminals.

Once i cranked it up it failed the diode test and also showed it only putting out 12v. i asked him to recheck it after the glow plugs turned off and that time it passed the diode test but still only showed it was putting out 12v. He checked the batteries and said they were good and had 12.71 on them.

He suggested i remove the alternator and have it checked inside on their machine. i haven't done that yet.

I'm just confused because my scangauge II shows 13.5 or so once the glow plugs go off. does that make any sense to ya'll? i put a meter on the batteries and i do not see a voltage increase once the engine has started running. the volts on both the batteries when the engine was off was around 12.41 and stayed at 12.41 after the engine was running. so, it doesn't appear that the batteries are charging but could that be because they don't need to be charged? just wanted to get a good direction for troubleshooting since the scangauge shows good voltage.

[03powerstrokeuser]

What year truck and how many miles? Also, is the tow haul light on? The alt. will usually test good on the bench and be bad. Mine usually runs @ 13.68-13.74 depending on what's running at the time/ ac, lights etc. Have you charged and load tested the batts?

[alexjeep]

My 04 died on me on the way to work one day. Did not have the scan gauge set on volts, but the radio died and then all the lights and gauges died all of a sudden. Was able to get off the road luckily. Definitly check the batteries. When mine died, none of the idiot lights ever came on and it never threw a code. It just died. Now I run with the one of the scangauge settings on volts all the time. When I put a meter on the batteries now, when the truck is running, they read 14.1 volts. Before the alternator went out I was getting similar readings to what you have now.

[chadc281]

I added my truck details to my sig, sorry about that.
no, tow/haul light was not on. I haven't charged the batteries or load tested them yet.

If the alternator will usually test good on the bench but still be bad then what's the best way to find out if it's actually bad?

[oldtechwiz]

Originally Posted by chadc281

I added my truck details to my sig, sorry about that.
no, tow/haul light was not on. I haven't charged the batteries or load tested them yet.

If the alternator will usually test good on the bench but still be bad then what's the best way to find out if it's actually bad?

The alternator WILL test good if it is good and bad if it bad on a bench test 'with a properly calibrated tester' designed for alternator testing. The reason for out of circuit testing of the alternator is to remove external influences like shorts, draw variations, etc from the test. A bench test basically runs the alternator at various speeds from idle to full rev at specific loads. Under each load, the tester checks the output of both phase diodes and combined output. If either diode fails (is open) output will fall providing lower voltage and current across/through the load. The readings are then compared to a chart for that alternator to determine variance from ideal.

The stock alternator from a ford f250sd should output 12.5v at idle with no diode fails and light load and above 13.52v at 1500rpm nominal load. Contrary to some opinions, the alternator run with no load will not hurt the diodes as there is no draw bing placed on them. The regulator on the other hand can run wide open without a load degrading it's life. This is why some say no load on the alternator will immediately kill it. The statement is true only if the regulator is part of the alternator and has already suffered prolonged damage.

I would, pull the batteries and fully charge and load test them. Replace them in pairs if either has a problem. Next fully charge the batteries (normally they are only charged to 80% on shelf) and install them. Do an in system test and make sure you check the grounds at both end of wires then proceed to start and run testing of the system.

[oldtechwiz]

Originally Posted by chadc281

I've periodically had some weird electrical issues, like the gas guage showing 0 and the windshield wipers not turning on but it's few and far between and usually starts to work fine after turning the engine off then back on. it was suggested to me that i get the alternator checked out so i went to autozone yesterday and they hooked up their checker to the pass side battery pos and neg terminals.

Once i cranked it up it failed the diode test and also showed it only putting out 12v. i asked him to recheck it after the glow plugs turned off and that time it passed the diode test but still only showed it was putting out 12v. He checked the batteries and said they were good and had 12.71 on them.

He suggested i remove the alternator and have it checked inside on their machine. i haven't done that yet.

I'm just confused because my scangauge II shows 13.5 or so once the glow plugs go off. does that make any sense to ya'll? i put a meter on the batteries and i do not see a voltage increase once the engine has started running. the volts on both the batteries when the engine was off was around 12.41 and stayed at 12.41 after the engine was running. so, it doesn't appear that the batteries are charging but could that be because they don't need to be charged? just wanted to get a good direction for troubleshooting since the scangauge shows good voltage.

The test procedure used to test the alternator in the truck will always fail the diode test. You must only perform a diode test on the bench. I would seriously check for bad grounds. What you are describing with panel features (no fuel gauge etc) is an indication that power from the batteries has dropped below 10volts.

[chadc281]

Originally Posted by oldtechwiz

I would, pull the batteries and fully charge and load test them. Replace them in pairs if either has a problem. Next fully charge the batteries (normally they are only charged to 80% on shelf) and install them. Do an in system test and make sure you check the grounds at both end of wires then proceed to start and run testing of the system.

When you say "do an in system test" are you referring to the same alternator test that autozone did or just checking voltages with my meter? Also, if my voltages did drop below 10 volts a couple of times and create the gauge problems, do i need to worry about FICM damage?

Also, as far as checking for bad grounds, other than the negative terminals to frame, where are some other ground locations to check. just wondering if there are a couple locations or a whole bunch scattered all over the place.

[chadc281]

how can i found out what size alternator i have? The alternator guy says i have a 95amp but the only replacement alternators i see on tousley are 110 amp.

Also, if i get a new one what size should i buy. tousley has a 140amp but its listed as dual alternator. if the 140amp will work, will i need to upgrade cables or anything else? i can't really afford the DC power stuff although it does look like good stuff.

[teamroper60]

The stock alternator should be a 110 amp model. I have seen people use the upper alternator from the dual setup (which is higher rated) with some success. After going through a few alternators myself, I am skeptical of using the small case alternators. They get too hot and heat kills the diodes....

[oldtechwiz]

Originally Posted by chadc281

how can i found out what size alternator i have? The alternator guy says i have a 95amp but the only replacement alternators i see on tousley are 110 amp.

Also, if i get a new one what size should i buy. tousley has a 140amp but its listed as dual alternator. if the 140amp will work, will i need to upgrade cables or anything else? i can't really afford the DC power stuff although it does look like good stuff.

While using a higher rated 1/2 of a dual alternator has been used by some it is not recommended. You can order, as I did, a 185amp direct replacement. Amperage Technologies is where I got mine. Above 150amp it is best to replace the hot from the alternator to the battery changing the 4ga fuse link wire with a 2ga fuse link wire.

On my 2004 f250sd the original wire had alternator to (2) 50amp fuse links plus (2) 50amp fuse links coming from FICM PCM plus a non-fuse wire from the firewall block all merging into a single connector at the battery. The problem with the stock cable is that while the alternator can deliver 110amps, the cables going to the batteries can only handle 100amps (2 x 50amp fuse links). Moving to the heavier 2ga cable with 200amp fuse link means removal of the complete old 4ga fuse links right up to the battery connector while keeping the FICM PCM and firewall wire intact. The new alternator delivers 145amps at idle, 185amps at 1500rpm and 195amps at 2500rpm. This is a big improvement over the stock one which delivers 85amp at idle, 95amp at 1500rpm and would blow the fuse links if ever called to deliver 110amps at 2500rpm. A cold engine with everything on (lights, heater, AC etc) would draw about 95amps at idle so you end up actually draining the batteries rather than charging them until the glow plugs cut out.

[bismic]

Originally Posted by oldtechwiz

While using a higher rated 1/2 of a dual alternator has been used by some it is not recommended.

Why is it not recommended?

[oldtechwiz]

Originally Posted by chadc281

When you say "do an in system test" are you referring to the same alternator test that autozone did or just checking voltages with my meter? Also, if my voltages did drop below 10 volts a couple of times and create the gauge problems, do i need to worry about FICM damage?

Also, as far as checking for bad grounds, other than the negative terminals to frame, where are some other ground locations to check. just wondering if there are a couple locations or a whole bunch scattered all over the place.

Clarification: 'In system test' refers to having the batteries and alternator fully connected. Test voltages at both batteries to frame, alternator to frame (without the vehicle running). This is also known as a 'DRY TEST'. Can't say for sure about the FICM as just inspecting the wiring schematic seems to indicate low voltage just prevents it from controlling fuel right. There are lots of grounds spread all over the truck that can cause problems for systems.

[oldtechwiz]

Originally Posted by bismic

Why is it not recommended?

Amperage tech told me that dual alternator set-ups vs single are slightly different. The fellow showed me a top-dual, bottom-dual, and single. They all had different pulley sizes and the single had a different serpentine belt width. The differences were minor 1/32" on belt width and 1/8" on pulley diameter but the tech said that's all it takes to degrade the system over time. He told me they have experienced bad tensioner tension allowing slippage, and excessive belt wear such that now they won't supply anything but the right Alternator for the intended use.

As a former electronics engineer, everything he said makes perfect sense. You can use pantyhose as emergency fan belt on old cars, and even extend an old clutch to function a few more miles with vinegar but they are best use to hi-lite shapely legs or garnish a salad respectfully.

[bismic]

Who keeps panty hose in their truck - lol. (sorry, couldn't resist)

The Ford BodyBuilders manual shows the 140A alternator to be an option - included w/ vehicles equipped w/ the snow plow package. Anyway, pulley size (diameter) by itself isn't the issue (if it really is different and I do not see that it is in the BB guide). I do agree though that belt tension is an important issue (as you mentioned).

140 AMPERES
Engine............................................ .........Drive Ratio..............Model Application
6.0L OHV Power Stroke Turbo Diesel V-8(1)...2.79:1 Drive Ratio.....Super Duty F-Series
6.0L OHV Power Stroke Turbo Diesel V-8.......2.49:1 Drive Ratio......E-Series
(1) Available on Super Duty F-Series w/Snowplow Prep Package only.

110 Amperes
Engine............................................ .........Drive Ratio..............Model Application
6.0L OHV Power Stroke Turbo Diesel V-8...........2.79:1............. Super Duty F-Series
6.0L OHV Power Stroke Turbo Diesel V-8...........2.49:1..............E-Series
2.79:1 Super Duty F-Series

I can post the electronic version if you need to see it to believe the above information.

Bottom line - Ford themselves installs the 140A unit as a single alternator in our trucks.

[24hrsparkey]

Originally Posted by bismic

Who keeps panty hose in their truck - lol. (sorry, couldn't resist)

The Ford BodyBuilders manual shows the 140A alternator to be an option - included w/ vehicles equipped w/ the snow plow package. Anyway, pulley size (diameter) by itself isn't the issue (if it really is different and I do not see that it is in the BB guide). I do agree though that belt tension is an important issue (as you mentioned).

140 AMPERES
Engine............................................ .........Drive Ratio..............Model Application
6.0L OHV Power Stroke Turbo Diesel V-8(1)...2.79:1 Drive Ratio.....Super Duty F-Series
6.0L OHV Power Stroke Turbo Diesel V-8.......2.49:1 Drive Ratio......E-Series
(1) Available on Super Duty F-Series w/Snowplow Prep Package only.

110 Amperes
Engine............................................ .........Drive Ratio..............Model Application
6.0L OHV Power Stroke Turbo Diesel V-8...........2.79:1............. Super Duty F-Series
6.0L OHV Power Stroke Turbo Diesel V-8...........2.49:1..............E-Series
2.79:1 Super Duty F-Series

I can post the electronic version if you need to see it to believe the above information.

Bottom line - Ford themselves installs the 140A unit as a single alternator in our trucks.

***************************************

Interesting, so did the 140 come in all snowplow package pick ups , or was it an option avalible with the plow package .
thank you , 24hrsparkey