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    Results 1 to 18 of 18
    1. #1
      Join Date
      Aug 2004
      Posts
      543

      Low 11V charge at idle but normal just off idle

      Hello all...bit of an odd issue here. Got low voltage at idle (11.5 or so), but the second it goes off idle its up to normal. Now the ground strap is brand new, as is the battery. The pulleys are a March serpentine setup, 75mm and 172mm for the Alt pulley and crank pulley so 2.3 ratio. Alternator is 3 wire and has plenty of power to run electric water pump, fans etc, but the issue is I have EFI now. So when I come to a stop and the ECU sees less than 12 volts it shuts down.

      Any thoughts?

      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver


    2. #2
      Join Date
      Mar 2005
      Posts
      345
      Get a better EFI system? No reason it should shut down at just under 12 volts. Cranking voltage is usually in the 10 volt range, maybe it is something in the tune? Bob.

    3. #3
      Join Date
      Oct 2014
      Location
      DFW, Texas
      Posts
      422
      Country Flag: United States
      No EFI system should shut down at 12v, i think there is a different issue. I've run a car off of 9 volts before..

      Sounds like you need a different alt, or perhaps a smaller pulley. AND you have some tuning to do.
      1972 Plymouth 'Cuda - Not LS-swapped, 5.7L Hemi [MS3 Gold Box], T56 Magnum 6-speed - 'Cuda Build Page
      1976 Dodge D100 - Warlock
      2016 Subaru WRX - E30 Tune

    4. #4
      Join Date
      Nov 2006
      Location
      Mountain Springs, Texas
      Posts
      4,488
      Country Flag: United States
      Did you put a voltmeter right at the EFI controller? Maybe it is seeing much less than 12 volts due to a wiring issue. Check your grounds too.

      Don
      1969 Camaro - LSA 6L90E AME sub/IRS
      1957 Buick Estate Wagon
      1959 El Camino - Ironworks frame
      1956 Cameo - full C5 suspension/drivetrain
      1959 Apache Fleetside

    5. #5
      Join Date
      Sep 2004
      Location
      Metamora, Illinois
      Posts
      1,614
      Was the voltage ever good, or did it just start. If it was good at one time, what have you changed since then? Also make sure you have multiple grounds connecting the engine/frame/body and they are all good clean solid connections.

    6. #6
      Join Date
      Aug 2004
      Posts
      543
      Quote Originally Posted by a67 View Post
      Get a better EFI system? No reason it should shut down at just under 12 volts. Cranking voltage is usually in the 10 volt range, maybe it is something in the tune? Bob.
      Its a brand new Holley Sniper...a better system would be a much more upgraded one. Im not an EFI expert, but I think cranking amps dont correlate to how many volts the system needs to run reliably. Ill look into that with Holley anyway.
      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver

    7. #7
      Join Date
      Aug 2004
      Posts
      543
      Quote Originally Posted by rocketrod View Post
      Was the voltage ever good, or did it just start. If it was good at one time, what have you changed since then? Also make sure you have multiple grounds connecting the engine/frame/body and they are all good clean solid connections.
      Actually the idle voltage has never been excellent, but it does have two brand new ground straps now. Maybe the 2.3 pulley ratio is too low for proper idle voltage?
      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver

    8. #8
      Join Date
      Aug 2004
      Location
      Jacksonville, FL
      Posts
      1,651
      Country Flag: United States
      What is your voltage reading off of the battery and alternator stud? I would look at those in addition to what RocketRod and Don said to do.
      Chris
      1968 Chevy Camaro SS
      LS3/T56 DSE suspension


    9. #9
      Join Date
      Aug 2007
      Location
      Jonesboro, Arkansas
      Posts
      2,506
      Country Flag: United States
      A lot of alternators don't "excite" (or start charging) until after a certain rpm. I'm thinking changing the pulley might create more rpm at the alternator without revving the motor up.

      Carl Wilson
      1968 Camaro - T-56 6 speed - 383 Stroker, 2014 Mustang GT seats. FiTech EFI, Tanks Inc. Tank with Deutschwerks fuel pump.

    10. #10
      Join Date
      Aug 2004
      Posts
      543
      Quote Originally Posted by 130fe View Post
      What is your voltage reading off of the battery and alternator stud? I would look at those in addition to what RocketRod and Don said to do.
      Ill check this and come back...

      - - - Updated - - -

      Quote Originally Posted by minendrews68 View Post
      A lot of alternators don't "excite" (or start charging) until after a certain rpm. I'm thinking changing the pulley might create more rpm at the alternator without revving the motor up.
      Thats what has me a bit confused...the second the RPM is off idle the voltage jumps to normal.
      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver

    11. #11
      Join Date
      Nov 2011
      Location
      Wylie, Texas
      Posts
      279
      Country Flag: United States
      What is the voltage at the point where the sense wire is connected? It should maintain 14V at this point at all times.

    12. #12
      Join Date
      Aug 2007
      Location
      Jonesboro, Arkansas
      Posts
      2,506
      Country Flag: United States
      At what rpm does your car idle?

      Carl Wilson
      1968 Camaro - T-56 6 speed - 383 Stroker, 2014 Mustang GT seats. FiTech EFI, Tanks Inc. Tank with Deutschwerks fuel pump.

    13. #13
      Join Date
      Aug 2004
      Posts
      543
      Quote Originally Posted by blitzer454 View Post
      What is the voltage at the point where the sense wire is connected? It should maintain 14V at this point at all times.
      I’ll check...if it isn’t?

      - - - Updated - - -

      Quote Originally Posted by minendrews68 View Post
      At what rpm does your car idle?
      Idle is steady at 800 or so
      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver

    14. #14
      Join Date
      Aug 2004
      Posts
      543
      So had a look at the ground straps, cleaned them up and idle voltage is now up to 12. Its odd though, the straps are brand new and the contacts werent particularly rusty. It seems to me like just 12 volts at idle is still low.
      Manuel Scettri
      ------------------------------------------------
      1973 Firebird - Pontiac 455
      1990 2 Door 4Runner - byebye
      1990 2 Door 4Runner - byebye
      2016 KIA Sportage diesel - The Daily Driver

    15. #15
      Join Date
      Sep 2010
      Location
      Beach Park IL
      Posts
      2,838
      Country Flag: United States
      You want 3:1 on the pulley ratio. So get a bigger crank pulley or smaller alternator pulley.....or raise the idle speed.

      Then check voltage at the EFI controller, if it doesn't match what the alternator is putting out, correct that.
      Donny

      Support your local hot rod shop!

    16. #16
      Join Date
      Dec 2010
      Location
      Fredericksburg, VA.
      Posts
      3,155
      Country Flag: United States
      Yep, your alternator is spinning too slow at idle. Like others have said you need a bigger crank pulley or smaller alternator pulley. I started with a stock March serpentine front drive kit and initially I had the same problem. At idle the voltage would drop off even with a 140 amp alt. It was pretty obvious to me that the alt was simply spinning too slow at idle even with a 1000rpm engine idle speed. I installed a smaller alternator pulley and the problem disappeared immediately. You could test this by simply raising the engine idle speed.
      Steve Hayes
      "Dust Off"
      68 Camaro

      Given sufficient initial acceleration, even pigs can fly!

    17. #17
      Join Date
      Jan 2006
      Posts
      385
      Country Flag: United States
      Quote Originally Posted by TheJDMan View Post
      Yep, your alternator is spinning too slow at idle. Like others have said you need a bigger crank pulley or smaller alternator pulley. I started with a stock March serpentine front drive kit and initially I had the same problem. At idle the voltage would drop off even with a 140 amp alt. It was pretty obvious to me that the alt was simply spinning too slow at idle even with a 1000rpm engine idle speed. I installed a smaller alternator pulley and the problem disappeared immediately. You could test this by simply raising the engine idle speed.
      Yes, the alternator pulley does help.

      Quote Originally Posted by dontlifttoshift View Post

      Then check voltage at the EFI controller, if it doesn't match what the alternator is putting out, correct that.
      Absolutely. Check ALL voltage taps on the ECM. I had mine where the battery tap was seeing full alternator voltage, but the switched igntion tap was 1.5V lower. Caused significant driveability problems until I discovered that discrepancy.
      1971 Camaro
      GM HT383, MiniRam EFI, AFR heads
      "8-speed" trans (700R4 + Gear Vendors OD)

    18. #18
      Join Date
      Mar 2009
      Location
      Houston, TX
      Posts
      1,193
      Country Flag: United States
      Also, where does the positive cable for the EFI connect to? Holley is very adamant that the + wire be connected directly to the battery.
      Tu Ho
      Firebird V2-LS swap





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