• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

Power loss from alternator

Nosferatu49534

Nosferatu49534

Well-Known Member
Messages
523
Reaction score
340
Location
Grand rapids
I've had this issue for a couple months now and it doesn't happen all the time. When I accelerate quickly and then let off the throttle it's almost like the alternator stop pushing power for a second or two. The volt gauge drops about 2.5 volts, maby a little more. I have built new battery, ground, alternator, and starter cables. All the ground connections have kopr kote on them. The hard part is it only does it when I'm driving so I'm not sure if I can do any physical tests to see what's happening. Any thoughts will be appreciated. If it doesn't make sense I can try to explain something better if needed.
 
Is alternator good? Mostly bearings have gone bad in my alternators. But a few have failed electrically.

Every time I have had low voltage fluctuations at the gauge it has been the drivers side battery positive post terminal was loose. Once it killed my alternator from the jumping back and forth from charge to not charging frequently to overheat.

Might want to clean the positive connection at back of fuse box near the brake booster too.
 
Im assuming it's good. I'll check the connections again and go from there. Can I tell by the housing which alternator I have 130, 144, etc?
 
Put a good quality volt meter on the system to see how much it's really fluctuating. Dash guages are notoriously inaccurate. I use a digital one that I can plug into the cigarette lighter and it's amazing how much different it reads.
 
If the alternator quits or looses ANY connection the tach will be the first to jump, flick, or quit. This includes the large charge wire being loose on the back of the alternator. IMO alternator isn't the issue.

Voltmeter dropping into the red:
Lets be clear that it is hard to drop two 850 CCA batteries and a 100+ amp alternator into the red on the voltmeter. It takes a 60+ amp load like glow plugs to do so.
Bad ground or power to voltmeter including the gauge cluster. This means pull and clean fuse contacts.
Bad, cracked connection, bad gauge, or other issue in the gauge cluster.
Bad ignition switch causing a "brownout".
Glow plugs, starter kicking on, or big short dropping voltage.
Let me expand glow plugs - yours should be ECM controlled, but, older ones and weird stuff can kick them on with loss of connection(s) to the controller. Likely at this stage you have a big short vs a bad starter or glow plugs coming on, but, fiction has to be plausible - the truth does not.
Bad battery or two.
Be aware the fusible links get old and can fail.
Wires can corrode internally.
Other things can drop voltage like rolling down a window or short elsewhere unrelated to the gauge, but, getting power off the ignition switch or same power feed.

Wiggle test with someone watching the gauge. Wiggle every harness - be careful as a bad (high resistance) spot can be hot enough (or suddenly get hot enough with hitting a short) to burn you. (Wear gloves and/or use a IR temp gun on the harness to look for hot spots.) Check the battery tray where the positive cable passes it for a intermittent short. Model year dependent the main power wire goes by the starter and is subject to insulation falling off causing a short.

Shorts as I refer to above are the hard to find arching shorts at less current than will burn the fusible links, burn the wire up, or burn the vehicle to the ground. These would be the easy to see and find failures.

Sometimes the price is worth admission at a good auto electrical shop to have them track down electrical issues.
 
Last edited:
A short some where would seem logical to me as it's an inconsistent occurence. All the major power cables should be good at this point. I'll start checking down the line farther and clean or replace all the fuses. That's not a bad plan any way as I'm pretty sure one of the previous owners messed around a lot with the electrical. There were so many extra feet of wire going to random lights and aftermarket switches. Plus there were incorrect fuses in different spots. 30's where a 20 was supposed to be and so on. I've been through them and at least have all the correct numbers for corresponding slots. Thanks for the info so far.
 
Is that replaceable?

Not sure if this solved it yet or not but I did find a loose screw I was using for the ground for my brake controller and holding my lift pump weather pack.

Could I set my self up a grounding bar under the hood specifically for small ground connections like my brake controller?
Say like this. Blue Sea Systems DualBus Plus 150A BusBar - 1/4 https://www.amazon.com/dp/B000K2MABA/?tag=jhuntlink-20
 
As an Amazon Associate we earn from qualifying purchases.
Nosferatu49534 said:
Is that replaceable?

Not sure if this solved it yet or not but I did find a loose screw I was using for the ground for my brake controller and holding my lift pump weather pack.

Could I set my self up a grounding bar under the hood specifically for small ground connections like my brake controller?
Say like this. Blue Sea Systems DualBus Plus 150A BusBar - 1/4 https://www.amazon.com/dp/B000K2MABA/?tag=jhuntlink-20
Click to expand...
It's built into the PWM regulator.
 
As an Amazon Associate we earn from qualifying purchases.
Well, I'm pretty sure I've got it figured out. When putting the exhaust on last night I had to unbolt the grounds to the frame by the down pipe and when putting the back on the bolt was stripped, not sure how I thought it was tight when I redid them a month or so ago. My buddy welded a nut to the frame right by the old hole and now they're bolted right there. I'll take a picture tomorrow. I didn't think about it yesterday. I didn't notice the issue this morning but I'll keep my eye on it.
 
You could use a busbar to consolidate a bunch of sensitive grounds but it would still have to have a good ground itself and be able to carry the combined current. Its kind of redundant except if you were grounding a bunch of stuff that needed holes drilled and screws added or were extra sensitive and you ran a good wire back to the battery.

The whole metal complex body, frame, engine is a busbar. You just have to make sure its inter connectivity is good ie frame to engine, battery to engine/frame, Body to frame, etc.

Fixing your engine to frame ground improves the connectivity of the overall metal busbar system.

keep us posted.
 
Yup, The bus bar would be just to clean things up and not have all kinds of screw holes in the body. There's a perfect spot just above the abs module to put a mounting plate.
 
Well I'm not sure why or how but the truck has been turning over slower and slower for a couple weeks, bought a new starter and went to my buddies to change it cuz he has a spare truck in case something didn't go well, (which has been normal for working on vehicles for me). He suggested checking all my connections before replacing the starting. Did that, got sorta better, but started getting slower again the next morning. I stopped and had batteries tested and the passenger was only putting out 350ish cca of 800. Figured that was my problem so I bought 2 new batteries.
255350517c3b45b9242112ea47f35b54.jpg

Unfortunately that didn't fix the slow starting. Replaced the starter as well and now it spins super fast. :) The best part though since I've replace the starter and batteries I've not had one problem with my "power loss" gauge fluctuations. Not sure how it fixed it but I'm happy. :) Would love to know why the battery went bad though.
 
How old was the battery? The best I had was an 18 year old Delco, original to my combine. The other only lasted 12 years. Today some last a year.
 
You must log in or register to reply here.
Back
Top