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7.3 IDI charging problems

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Dr. Magnus, Aug 6, 2016.

  1. Dr. Magnus

    Dr. Magnus Registered User

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    Ok, so the best way to do this is probably to explain everything from the beginning. I bought my truck about 3 1/2 years ago now, and since then It has haunted me with the same problem. It started about a month after I bought the truck, I had replaced the alternator with a new one as the old one (likely factory original) was completely dead after a month of driving. I replaced it with a new unit as well as the voltage regulator, and not just a couple days later it tested bad as well. I had that alternator replaced and the new one seemed to serve me well for the next several months. It should be noted that the battery dummy light only came on when these first 2 alts went bad. After I moved from Florida (where I bought the truck) to Missouri (where I currently live,) I noticed my batteries were going dead as the temprature dropped. the dummy light wasn't coming on, but the voltage on the dash-mounted voltmeter wasn't climbing above 12 volts when at idle with ANY accessory on (ie: headlights, A/C). I didn't realize that the alt was bad, assuming bad batteries because i lacked the knowledge. 1 set of new batteries later, and they were dead in a week. After finally figuring out it was the alternator, i decided to buy my new alternator from somewhere else. I had been buying them from advance auto parts, and decided I would try autozone (caus they have a lifetime warranty on these things) and I was very please with the performance. I replaced both the voltage regulator and alt again, and this time even when idling the voltage never dropped below 14 volts. Until a couple months ago, this was working fine, but then the old problems came back, except this time when i had the alternator bench tested, it tested fine, the handheld tester however said the voltage regulator was bad so away it went. The man at the autozone warranty'd my alternator anyway despite it testing ok (i tested the new unit as well before installation) and the problem still exists. ive thrown 3 more voltage regulators at the problem and it still won't go away. Ive had grounded the voltage regulater casing to the negative battery terminal and testing the alt wiring harness for resistance didn't reveal anything. Please help:frustrate I need this truck to work and hooking it up to a battery charger every morning is getting frustrating.
     
  2. franklin2

    franklin2 Full Access Member

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    When you turn the key to run but do not start the engine, is your little battery light coming on?
     
  3. DaveBen

    DaveBen Supporting Member Supporting Member

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    This sounds like a ground problem. Are the battery cables clean and corrosion free at BOTH ends of the cables? Is the alternator grounds tight and clean? Start looking in these areas and let us know what you find. These trucks demand high current for starting and that is why you need the third battery.
     
  4. Dr. Magnus

    Dr. Magnus Registered User

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    The battery cables are relatively new, and corrosion free. It seems that the previous owner replaced them before I bought the truck. but I did have to replace one of the negative battery terminals because the terminal was too loose on the battery. the truck starts just fine when the batteries are charged, its just that the alternator is not putting out more than 12.7 volts at idle. and even less if I have the AC or lights going. I should mention now that if the engine is revved up to above 1200 rpm then I can usually get around 12.9 - 13.2 volts, but revving any more will not make the number climb higher. I should note that even after testing all these wires, even though none of them show exsessive resistance, the truck is not without its strange electrical gremlins. Sometimes while driving at night the headlights will flicker on and off and I have to stop on the brights switch to fix it. The glow plug system has never worked quite right either, as I tested each glow plug, and all of them tested good, but the system still refuses to do anything but make that clicking noise when i turn the key. Strangely enough, taking the truck through a car wash during winter (doesn't matter if it's freezing conditions) will make the plugs work as intended for a couple days. So i had suspected some sort of bad ground for that, sorry for the wall of text, I'm just trying to give as much info as possible about the problem.
     
    Last edited: Aug 6, 2016
  5. Dr. Magnus

    Dr. Magnus Registered User

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    yes, the light is coming on before i turn the key.
     
  6. OLDBULL8

    OLDBULL8 Good Morning Ya'll. Supporting Member

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    It would be nice to know what year truck your talking about. Put it in your signature.

    Firstly, your voltage regulator case has to have a good ground, screwed securely to the body/chassis.

    The wires connected to the VR have to be clean, no corrosion.

    The green wire from the in cab VM to the alternator has to have a good clean connection at the Alt.

    The 12.3 to 12.7 voltage is typical at idle speed.

    At 1200+ RPM, after a start, the Alt. should put out 14.5 to 14.7 for just a minute or two, then reduce to ~13.3. The in cab (dash) VM is not very accurate, actual voltage should be measured with a Digital VOM.

    All things aside, you could switch to a 3G Alt that has an internal voltage regulator.

    Those damn external VR are known to give a person a lot of troubles. With your key OFF, check it for any voltage on all connections, there should be NONE.
     

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  7. chris142

    chris142 Full Access Member

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    Mine eats brushes for some reason.i just buy brushes and swap em in.
     
  8. Dr. Magnus

    Dr. Magnus Registered User

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    Ah yes, it's a 1989 f250 standard cab with a ZF5 transmission. The main problem I'm having with this is the fact that driving around town with the truck in this condition with the AC on, my battery will not charge. With the AC on at idle the voltage drops enough to not charge he batteries, and instead draw from them. You said this behavior is typical no? Is there any way to get the performance I was seeing back? And you were talking about the in cab voltmeter, all the mesurements i've been given were taken from a DMM, but is there a way that a faulty connection to the in cab meter would cause this? if so would disconnecting or bypassing it solve the problem? I know mine is slightly faulty, and will read a voltage that is lower than what is actually at the batteries.
     
  9. 79jasper

    79jasper Chickenhawk

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    Adjust the idle up?

    Sent from my SAMSUNG-SM-G935A using Tapatalk
     
  10. Dr. Magnus

    Dr. Magnus Registered User

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    the problem with that is the batteries don't start charging until roughly 1200 rpm, so thats right out. but that may make a good temporary fix. I have to take the truck out tonight, so i will see how it behaves.
     
  11. 79jasper

    79jasper Chickenhawk

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    As oldbull8 said, do the 3g alt.

    Sent from my SAMSUNG-SM-G935A using Tapatalk
     
  12. Dr. Magnus

    Dr. Magnus Registered User

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    :/ the problem is I just don't have the cash or time to do that right now. All the replacements I have had have been covered under warranty. I was hoping maybe there is some wore or something I could replace to fix this. But if that is the only option I guess I will have to live without AC this summer.
     
  13. OLDBULL8

    OLDBULL8 Good Morning Ya'll. Supporting Member

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    You say you have to hook up a battery charger every morning to get it started. When your thru running for the day, disconnect the negative battery cables for the night, then reconnect in the morning, see if the truck will start then. You may have a current draw from something during the night.
    Are you sure any in cab light is not on when all doors are closed ?

    What is the idle RPM ? It can be set as high as 850 RPM idle.
     
  14. Dr. Magnus

    Dr. Magnus Registered User

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    The situation seems to have changed a bit. Now if I keep all loads off the electrics then it will charge at a happy 14.5 volts, and idling it will stay at about 13. BUT that is with all loads off.
    Yesterday I was careful about not using the AC before I turn the truck off for the day and I was able to start my truck fine this morning. I will disconnect the batteries tonight though to compare voltage measurements.
    The idle is set at about 700 rpm
     
    Last edited: Aug 7, 2016
  15. catodd

    catodd Registered User

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    I have had the same problem for years on my 92'. I have been replacing seems like every 3 to 6 months the alternator or regulator.....I have put a ground wire from regulator to alternator etc.....I finally had enough and just converted to a 3G alternator this weekend...easy to do, I ordered everything off Ebay. View attachment 66735 View attachment 66736
     

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