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Do I have a charging problem?

Discussion in 'Chevy Trucks' started by 70monte, Jul 19, 2010.

  1. 70monte

    70monte Senior Member
    Messages: 468

    This is on my 98 K3500, 7.4L. Tonight my volt gauge was showing half way between the 9 and 14 on the gauge. I hooked up my Autoxray 6000 scanner and it showed 12.9-13.0volts at idle with the lights and AC on. I also had my utility trailer hooked up and it has 11 lights on it. I turned off the lights and AC and the scanner showed it only went up to 13.1-13.2 volts at idle. The outside temp was about 83* and humid.

    Like I mentioned in my previous post about my battery, the battery is only seven months old and tested good. The alternator is a new 124amp AC-Delco reman that was put on about seven months ago. I also just installed a new GM positive side battery cable and cleaned the contact points where the negative side cable hooks to the engine block.

    All the info that I've read on charging systems says that it should be about 13.3 volts or above for a good charging system. Is this true or are my values acceptable under the circumstances?

    If not, what else can I check or do to get the volts up. My 98 K1500 with the 5.7L and 105 amp alternator always shows over 14 volts on the scanner and gauge even with lights and AC on. The alternator on this truck was put on a few years ago and was a brand new AC-Delco unit.

    Do you think I need to put a brand new alternator on it instead of the reman and the used one before it.? Thanks for any ideas.

    PS I haven't been able to test the Amp output of the alternator yet because I've misplaced my multimeter.

    Last edited: Jul 19, 2010
  2. vegaman04

    vegaman04 Senior Member
    Messages: 378

    Try the big 3 upgrade. This involves replacing the power wire between the battery and alternator, the ground from the battery to the chassis and the ground strap from the engine / tranny to the chassis. Use quality connectors, clean all connection points. I did this with mine, has since moved it past 14vdc on startup, and after driving for a while (fully charged), down to 13.7vdc.
  3. 70monte

    70monte Senior Member
    Messages: 468

    Thanks for the reply. I just replaced the positive side battery cable with a new GM cable which has the power wire between the battery and alternator built into it. Do I need a heavier gauge cable?

    The negative side cable is still in good shape with no corrosion at the battery connection and the connection point on the engine block was cleaned, the stud, cable end, and engine block. Do I need a heavier gauge cable for this side?

    The ground strap between the chassis and the engine is original. I did remove the one end from the chassis and cleaned everything there but did not do the end that connects to the engine since its in a hard to get to spot. The strap probably needs to be replaced since its not in the greatest shape. Is this strap that important for the charging system.? Does this strap need to be heavier gauge than the original? Thanks again.

  4. lotec25

    lotec25 Member
    from Florida
    Messages: 47

    If you hook a Volt/Ohm meter up to the alternator how many volts is it putting out with no load? and then do it with load? The straps are a very big part of the charging system the Ground strap from chassis to engine etc etc are subject to a lot of salt/wear and tear, i would check them also with the Volt/Ohm meter make sure you got some good solid grounds.
  5. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    If it's truly accurate it's too low Wayne. So a few things to further diagnose but start with what's already been discussed (checking voltage at the battery to confirm if the gauge is even accurate).

    Note, these tests are most accurate with the engine running and all possible accessories turned on.

    Use a digital DVOM and check for voltage drop both on the positive side of the system as well as the ground side. Everyone thinks to check the positive side but few think to check for DROP on the ground side. Start at the battery (with the engine running) and check for drop from the neg terminal to directly on the alternators case. Then check from there to the cab/body, and then from the engine to the frame looking for less than a .5V drop. If that all checks out...

    Next check positive voltage first at the battery between the terminals. Then check it directly at the charging stud on the alternator while first grounding your test lead to the neg battery terminal AND THEN on the alternators case. If there's more than a .5V difference then you have excessive resistance in the circuit somewhere. Back track to pinpoint exactly where the issue lies.

    However if you find everything ok so far the next thing to check is that the alternator is staying in a charging state as it should. For it to do so there must be between 9-10.5 volts on the exciter wire at the alt. It will be the one labeled with the letter "L" in the connector plug on the alt. You need to verify that that wire is sending the required voltage to the alt to keep it "excited" and it needs the previously spoke of 9-10.5 volts to do so. Try to check that one while it's indicating a low voltage condition on the gauge (or meter if that's the case) for the best accuracy during the test.

    I wouldn't be a bit surprised if you find an issue down at the starter on the fusable links either. Very common cause of showing low voltages in the cab even though it may not really be the case.
  6. 70monte

    70monte Senior Member
    Messages: 468

    Thanks for the ideas and things to check. To first clarify something. My readings when the truck is first started or its cold out has always been fairly normal. This winter the dash gauge would read over 14volts and only go just below the 14 when it warmed up. During the spring and summer months when I first start the truck up, the dash gauge will show one mark below the 14 and go down from there after the truck gets hot. I have noticed this voltage drop on other vehicles in the past but I don't know if its considered normal or not. My 98 K1500 doesn't seem to experience this.

    I assume I want to do these tests with the truck fully hot. I'm not very knowlegable about using a DVOM so I'll probably ask some dumb questions.

    1. To test the chassis to engine ground, do I put a lead from the DVOM on each end of the ground strap or just from any point on the engine to any point on the chassis. Do I need to do this also for the ground strap that goes from the chassis to the firewall? The chassis to engine and chassis to firewall ground straps share a mounting point on the chassis if that makes a difference. I have cleaned and retightend this area as well as the ends of both straps.

    2. To test the exciter wire in the alternator connector plug, I unplug the connector and put the negative lead from the DVOM on the negative post of the battery and the positive lead to the L in the connector Plug? Is this correct? If it reads below the 9-10.5 volts, am I looking for wiring damage to the connector or something else?

    3. Do I need to test from the negative side of battery to where the negative battery cable bolts to the engine block and if so, am I looking for the same less than .5V drop?

    When I replaced the positive side battery cable. I unhooked the wires to the starter and did not notice any damage to any of them but I really don't know how to tell if a fusable link is bad. How do you tell?

    I will do these tests tomorrow and post the results. Thanks again.

  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    It's completely normal for voltage to start out higher during a cold start and especially so in cold weather and then taper back slightly to normal running voltage. You'll notice it more on some vehicles than others simply due to the fact that OEM gauges are not all that precise. If you ran a digital meter right on the battery/alt that was visible from the driver seat you'd see that it starts out a little higher and then tapers back to around 13.5-14.2. Which is where it should be on a perfectly operating system regardless of outside electrical loads. It's never a bad idea to check voltages both right after a cold start and again after it's been running for at least 30 minutes. This give you a comparison as to how the system responds as the heat is increased on all the components, including excessive resistance from a poor connection etc.

    Keeping your questions in order....

    1) When checking for drop on the ground side between the battery/engine/frame/body simply touch the leads directly to those components. Use a good clean location, on the engine for example use something on the engine that bare aluminum since it will allow you a good contact. On the frame or body you want to sand a small section to clean bare metal but actual locations aren't critical. As long as your leads are making a good connection that's all that's important. But note, your example of using the actual locations where a ground cable may be connected is not a good idea and many make that very mistake. Doing that may show the cable itself is ok but the actual physical connection between the cable and whatever it's connected to may be faulty...thus skewing your test. Instead, test near but NOT on that connection. That way your testing not only the cables integrity but the integrity of the connection to whatever it's attached to, which is where most electrical issues/excessive resistance actually lies. Typed text may make this appear a little confusing but it's not complicated and should make perfect comprehension if you think about it for a little.

    2) Testing the exciter wire should be done with the connector plugged into the alt and the engine running or else the test isn't conclusive. Being that I highly doubt you have an inline test pigtail on hand for a GM CS series alternator the only way for you to accurately do it is to pierce the wire insulation. I generally condone testing in this manner since it breeches the integrity of the insulation but for a DIY check it's the only way. If you do need to check it after all your other tests are complete be sure to seal the wire back up well with some tape or a dab of silicone. Plus that wire isn't in a highly corrosive area so it's more than acceptable practice in this instance if needed.

    3) Same thing as I described above. Don't test at the connection point, test near them so you're also testing the physical connection points. But yes you're looking for less than a .5V drop. .1-to-zero would be even better.

    Checking fusible links is mostly a visual due to their locations often times and OHM testing isn't practical on them either. Not something thats easy to test with a meter for voltage drop under running conditions and with the exhaust hot so a visual is in order. You're looking for corrosion right where the wire enters the plastic housing. These tend to trap moisture (especially at the starter) thus they corrode internally. Usually if you bend the wire right where it enters the plastic housing you'll see some green if there's any corrosion going on in there. If you see any those fusible links should be cut out and replaced immediately. In an ideal world they'd be eliminated and replaced with Maxi fuses in a better location (which I often will do during upgrades) but it's not practical on a truck such as you're simply due to the effort required.
  8. 70monte

    70monte Senior Member
    Messages: 468

    Thanks for the clarification and information. I will see what my results are. Thanks again.

  9. 70monte

    70monte Senior Member
    Messages: 468

    I did the tests that have been suggested today and here are the results. This was with truck running, AC, lights, radio, and blower motor on high.

    1. volt measurement at neg & pos battery posts 14.3 cold, 13.75 hot after about 45 minutes of running
    2. volt measurment at neg batt. post and alternator stud 14.52 cold, 13.88 hot
    3. neg batt post to alternator case .06 cold, .07 hot.
    4. neg batt post to cab .11 hot
    5. chassis to engine .01 hot
    6. from pos batt post to alternator stud, .11 hot
    7. from post batt post to right before fusible link inline to alternator .01 hot
    8. from right before fusible link to right after fusible link. .00 hot
    9. from right after fusible link to alternator stud. .01-.02 hot
    10. from neg batt post to engine. .01 hot

    The volt gauge inside the truck was at the mark right before the 14volt mark when I first started it up. right before I was done, the gauge was 2 1/2 marks before the 14 mark so I'm going to assume that my gauge is bad.

    Before this test I replaced both of the braided ground straps that go from chassis to engine and chassis to body with new ones. The strap that went from chassis to body was very rusty where it mounts to the firewall. This is right under where the heater hoses go into the heater core. I could not undo the nut and the strap ended up breaking at this point. I had to attach the new strap at a different point on the firewall.

    I looked at the wiring at the starter and everything looked good. I also didn't see any fusible links down there but some of the wiring was covered in a silver type wrapping.

    I did not get to test the "exciter" wire since I ran out of time but I think everything looks within specs unless I'm reading the results wrong. 0.11 was the highest result I got on any of the test points which is well below 0.5 I didn't go drive the truck at any point so I don't know if that made a difference in the results but it was very hot under the hood by the time I got finished.

    Let me know what you think.

    Last edited: Jul 21, 2010
  10. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    At this point it appears that all your specs and connections are good. But to clarify, when you have 13.75V right at the battery is this when the gauge appears to be reading out of the ordinary from where your used to seeing it run (ie 14V on the needle)?

    Because as I mentioned before the OEM gauges are not very precise. A small .5 or 1V drop at the battery as run time and temps increase can show as several volts at the gauge; thus making you believe there's a problem when the real problem is simply inaccuracy in the gauge. Coolant temp and oil pressure gauges are the same way. Not to be trusted for real monitoring purposes.
  11. 70monte

    70monte Senior Member
    Messages: 468

    Yes, when I had 13.75 at the battery, the inside gauge showed 2 1/2 marks before the 14. Since I have owned this truck, the gauge has always gone below the 14 volts mark when it gets hot, its just not as much during the winter. I guess I've been comparing it to my 98 K1500 which never goes below the 14v mark. So I guess I could say that the gauge has never really read normal, but pretty close during the winter months when it was very cold.

    The other reason I have thought there is a charging issue is that I'm on my third new battery in 2 1/2 years. Surely my luck is not that bad.

    The only other thing that I don't understand is that when I had it hooked up to my scanner the other day, it showed 12.9v under the hot conditions. I should have hooked up the scanner today to see what it showed. Maybe I'm not getting a good reading at the OBDII port or have some wiring issues from the battery or alternator to the port.

    After seeing the condition of the chassis to firewall ground strap, I doubt it was doing its job at all. Putting a new one on did not change the gauge reading at all though.

    I guess I will just keep an eye on it and see what happens. Thanks for all of your help.

  12. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Three battery's in 2 1/2 years (with two different alternators) can only really be caused by a couple things. Either the battery's you're buying are substandard (not at all uncommon from the big box stores) or the battery's are being subjected to a low charge for lengthy periods, either from long periods of non use or too much short trip driving cycles or a combination of both where the battery never has a chance to be fully recharged. Today's run of the mill battery's won't tolerate that for long. It can take up to a 1/2 hour of run time for a battery to fully recharge from just a single start depending on circumstances. Combine a couple of those together per day for a year and it's easy to see how they can be running on a low charge.

    Don't be too concerned about the voltage readings you're seeing through your scanner as I've never found them to be too accurate since the 12V lead in the OBD connector is basically at the end of the system. In fact I often find it to be as far off a 1.5V low during a key on engine off quick check on a perfectly healthy system. This is why using a meter directly at the battery is still the best and most accurate method for checking actual voltage. If you'd like to monitor it for a while you can always run a couple leads in the cab from the battery for a quick check any time you'd like. Just be sure to add a 10 amp fuse in the 12V wire for safety. I do this quite often when diagnosing charging issues.
  13. 70monte

    70monte Senior Member
    Messages: 468

    I've been buying batteries through O'reilly's which supposedly are made by Deka. The truck does sit a lot but when it is driven, its usually for more than 30 minutes. If this battery goes bad, I will get one somewhere else. I will keep an eye on the voltage periodically but will pretty much disregard the inside gauge.

    My fiancee's grandmother has a 97 K1500 that only has 21,000 miles on it and its used as a farm truck so most of its driving is done running around the farm. It sits most of the time though. The battery in it is a three year old MAXX from Walmart and it always starts up fine. I will probably use one of these batteries next time.

    I want to say thanks again for all of the help. I really appreciate it. This site has probably helped me with various truck problems more than any other one. Take care.

  14. lotec25

    lotec25 Member
    from Florida
    Messages: 47


    Glad you figured some stuff out, I know the problem might not be fixed but at least you know everything is good. If i had to make a educated guess now I would vote on those batteries not being the best.

  15. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    No O'Reilly's around here Wayne so I can't say who produces their battery's and to who's specs but I believe you're on the right track to try a different brand. Guy's do seem to have good luck with the Wally World battery's from what I've seen so that may be a viable choice the next time around. Being able to exchange them 24/7 is the biggest advantage.

    The newer Diehard's Platinums are now manufactured by Odyssey and are an exceptional battery for the investment if you have a Seas center around so you may wish to take that into consideration as well.

    Happy to assist as always.
  16. 2COR517

    2COR517 PlowSite Fanatic
    Messages: 7,115

    Talked to a fleet manager (70+ cars) the other day. Has tried dozens of Deka/Napa batteries, refuses to buy another.

    We see very, very few failures with the Duralast (Gold) batteries, which are manufactured by Johnson controls to AutoZone specs. Much higher failure rate with the Optimas, at least in the red top category.

    Wayne, I don't know if you have dual batteries, but if you're buying pairs, look for matching dates. The AZ batteries have year/month stickers on the sides.
  17. 70monte

    70monte Senior Member
    Messages: 468

    I have a friend whose nephew has worked for O'reillys for quite a few years and the nephew has said that the O'reilly's batteries are junk. I'm beginning to agree.

    I do have a Sears service center here and will keep it in mind. The Walmart MAXX battery for my truck is $77 which is hard to beat price wise. I paid $95 for the O'reilly's battery I have now. I have also considered the Duralast. If this current battery goes bad, I will try one of the three up above.

    I hope my problem is fixed if I had one to begin with

    I only have one battery on this truck. Thanks again guys.

  18. 70monte

    70monte Senior Member
    Messages: 468

    Bringing this post up again because I had to replace the battery again because it went bad. This one lasted a little over two years. Truck wasn't starting as well as it had been and gauge was reading lower on a more consistant basis so I hooked up my battery tester to the battery and I only had 12.4 volts and 200 CCA's on a 800 CCA battery and the tester said the batter was bad. Took the truck to O'reillys and it tested bad there as well.

    I told O'reillys that I wanted a refund instead of a replacement battery since I was still under the 3 year free replacement and they gave me the refund. I went to Autozone and bought a Duralast Gold. I will see how this one will hold up.

    I think what B&B said up above about too much sitting and the battery never staying fully charged are bad for the battery is what my problem is. I only average about 2,000 miles a year on this truck so it does sit a lot. I'm going to try driving it more often so maybe this won't happen again so soon. My other truck sits just as much but doesn't seem to have this problem but of course I have never had an O'reillys battery in it either.