Voltage fluctuations

Discussion in '2005+ Mustang GT 4.6L Tech' started by DiMora, Aug 27, 2015.

  1. Pentalab

    Pentalab forum member

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    Potential issue with any UDP is.... at idle, the alternator is spinning slower. Do folks really see any hp/tq gains with the use of a UDP ? Heck, ur water pump /alternator / AC and everything else will be spinning slower.
     
  2. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
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    The UDPs do indeed slow down the accessories but there have been no reported issues with UDPs on a 4.6 3V. I've certainly have no issues on mine and my AC still blows cold on a 115*F day.
    As for power gains, you're looking at roughly 9hp and 8lbft to the wheels so that's less than $30 per HP.
     
  3. DiMora

    DiMora More Is Better

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    I do not have UDP's.

    I fixed it - it was indeed the alternator going bad. I had a spare (actually I have two spares...one is the 8 rib off of Skwerl's old car)...but I used the 2008 spare I had laying around and ground the ears off and installed it.

    It works great...idles at around 13.5 and is stable not only at idle but throughout RPM changes.

    I might order that American Muscle rebuild kit and get the bad one back in good order in case this one goes bad. Or...bite the bullet and order an Innovators West Balancer and go 8 rib.

    I would also need a Roush 8 rib blower pulley - any idea who sells those for a single-belt system Roush TVS R2300?
     
  4. DiMora

    DiMora More Is Better

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    Alright, the alternator I installed in post #23 on 9/5/2015 died this week. Battery is a nice Optima yellow-top beast (deep cycle capability) - so fortunately it did not harm my battery when it died. It was weird to watch the voltage drop off on my AeroForce interceptor as the battery lost voltage when the alternator died...first the traction control light turned on...then the ABS...then the battery idiot light...then I lost tach and speedo...then the car started to run rough and I pulled over. My wife brought me my Honda generator and my Optima battery charger - and I enjoyed some food at a local restaurant while it charged up, then I made it the last few miles home after my battery had a full charge.

    So, deciding I'm tired of these crappy OEM Motorcraft 6G alternators, I installed a DOB bulletproof Denso unit I had bought a while back. That took some fabrication, as I ordered a rear Denso mount bracket from Roush that holds the rear end of the alternator to the supercharger's intake manifold...but the bracket did not match the orientation of the DOB alternator...or the OTHER DOB Denso alternator that I have (off of Skwerl's wrecked Bullitt), so I had to fabricate / weld up a modified bracket. Got that done, got it painted, installed...and I'm back in business.

    However...here are my voltages read off my Aeroforce Interceptor (OBD-II plug):

    Idling: 12.0-12.6
    Cruising: 12.6-13.1

    IAT's are around 127

    Does that seem normal? (Voltage seems a bit low to me). Perhaps I should datalog voltages with my SCT....

    Edit...I saw Bruce posted 13.3 is reasonable when it is hot out...I guess I'm close at 13.1 to that.
     
    Last edited: Jun 22, 2019
  5. Pentalab

    Pentalab forum member

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    I'm reading 14.4 vdc on my aeroforce gauges, idle or cruise, or wot....... yet am reading 14.751 vdc with my calibrated Fluke 87 DVM.... with probes stuffed into the tops of the battery terminals. The aeroforce gauges ( all of em on A pillar) read .35 vdc low. I also used a megabuck HP lab style DVM on battery posts..and also got 14.748 vdc.

    2 weeks ago, my 2011 Fusion would not start. Jump started the Fusion...and read 14.1 at idle... with fluke 87a with probes into battery posts.

    Battery in mustang reads 12.5 with eng off overnight. New battery in Fusion reads 12.2 vdc... with eng off overnight.

    The above readings were 2 weeks ago....and since I had the hood open on both cars , facing each other, and test gear out, took readings on both vehicles.

    Try using a dvm, with probes into battery terminals. I suspect your aeroforce gauges may be receiving a correct reading, but a V drop is taking place some where in the wiring. Use the same dvm..and take readings in several places... like any 12 vdc aux jacks in cabin..... output of alternator etc.

    While ur at it... switch DVM to read AC Volts....and then you can read any ac ripple. I'm seeing <20 millvolts....at idle. If u read sky high ac ripple, 1 or more diodes have shorted inside the alternator. (6 in total...since the alternator is 3 phase).

    The fluke DVM's read AC.... and block the dc component since they use block caps in each test lead... internal to dvm. My B+K DVM does not have block caps, so it reads 14.75 vdc... when switched to AC V mode....so can't be used to read ac ripple.
     
  6. 1950StangJump$

    1950StangJump$ forum member

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    Sorry, just saw this. I also have the Aeroforce.

    Because I have the KB, I couldn't do the DOB option (won't fit). So, I went with the 200 amp PA Performance alternator. I upgraded last summer because the stock alternator was fluctuating wildly, and because I put in a dual fan HE that allegedly pulls near 30 amps all by itself.

    When first starting the car, the Aeroforce reads around 14.0. If it's cold outside, it might read 14.2 or 14.3. This reading is very temperature dependent.

    As the car is driven, particularly in heat, it falls to the 13.7-13.9 range. Reading up on the subject, I think we are seeing resistance build in the wiring from heat that skews the computer measurement of the volts in some way especially through the OBD-II; I don't believe I am seeing actual system voltage drop . . . at least in any material way. I can be running the A/C, both HE fans, the IC pump (obviously), the radiator fan, blasting music, and have all lights on . . . the car doesn't show the slightest hiccup to indicate voltage concerns. The voltage reading just plain gets lower as under-hood temps climb; what I have sucking power doesn't seem to matter beyond the normal temporary drop in voltage readings when you first click an item on.

    For what its worth, when I talked with DOB last summer, the guy swore the fluctuations were a characteristic of the 6G alternators, and his wouldn't do that. Well, sounds like it does (at least for you).
     
  7. DiMora

    DiMora More Is Better

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    I put a multi-meter on it. My Aeroforce appears to read .2 V low. I'm at 13.2-14.0 at idle if I probe my right front ground bolt and fuse box power points (my battery is in the trunk).

    AC voltage is showing .8 mV so it looks like my diodes are fine.

    Per Jason/DOB's recommendation, I'll be ditching my Optima yellow-top and trying an Interstate Battery to see if it performs better (Perhaps my Optima is crapping out on me and causing a voltage-suck)
     
  8. Juice

    Juice forum member

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    Put the multimeter on the battery and compare readings to the OBD port output (what the PCM thinks the voltage should be.
    This test will tell you if there is a voltage drop in the wiring.

    I agree, seems a little low. I would be ok with 13 at idle and close to 14 running.
     
  9. DiMora

    DiMora More Is Better

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    I did; it (AeroForce) reads .2V lower than actual voltage.
     
  10. Juice

    Juice forum member

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    0.2 v difference is negligible for voltage drop for a trunk mounted battery.