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Thread: EFI/Coil MS3 conversion 29V/dash issue

  1. #1
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    EFI/Coil MS3 conversion 29V/dash issue

    1st issue:
    Anyone have issues before starting where you see 29V at battery voltage on PerfectTune gauge?
    Also TPS shows 173%.

    If I shut off/ turn on key a few times it will go to normal.

    I also have to make sure it is reading TPS before turning starter to see that MS3 is functional.

    Then car will start.

    2nd issue:
    When key is out, the "battery" idiot light on the right shows a very dim light.
    If emergency brake is up that light will also be very dim.

    I have changed out those bulbs for LED replacements.

    Any ideas for either of these is appreciated.

  2. #2
    Senior Member
    Join Date:  May 2011

    Location:  Norton, MA

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    My VIN:    767 (3.0L EFI/EDIS)

    I don't have a specific suggestion, other than checking grounds and power to MS. I screwed up my MS ground wiring originally, but caught it before I did any real driving. I don't exactly remember what I did wrong, but it wasn't getting enough power. I feel like I screwed up something with the main power wire too, but it's been a while.

    Do the gauges look right in TunerStudio? I'm not familiar with PerfectTune.

    My TPS binds (after pushing the gas, it doesn't go back down to 0 when you release the pedal, until I loosen the screws from the throttle body), so I had to disable it and run without a TPS, but someday I'll get around to figuring out what's wrong with that.


    As for the bulbs, that I can comment on, even though mine aren't LEDs yet:

    - The alternator relies on the load of an incandescent bulb to work properly. If you put in an LED, you need to put a resistor inline so that the current draw is the same (or at least I'm assuming that works; I still have the incandescent).

    - The brake light might be a similar issue, except here it's that the brake fluid cap has a sensor in it that will turn the light on if the brake fluid is low. I'm pretty sure it's a switch, but it may be that either the e-brake, the brake fluid cap, or both are slightly making contact just enough to make an LED glow but not an incandescent bulb. You might be able to test this with a multimeter, but I'm just making wild guesses here.

    I do wonder if the resister solution really works, or if it's going to cause a slight constant current draw, but I assume the same draw is occurring through the incandescents already, just not enough to make them light up.

    -- Joe

  3. #3
    '82 T3 FABombjoy's Avatar
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    Quote Originally Posted by NorthEastJBD View Post
    1st issue:
    Anyone have issues before starting where you see 29V at battery voltage on PerfectTune gauge?
    Also TPS shows 173%.
    Do tunerstudio gauges agree? If so your calibrations are in outer space.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  4. #4
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    EIN - Did you ever find out why your MS cut was cutting out on you on way to NERD meet?

    The Tuner studio is showing the same as the Perfect Tune gage. The TPS was fully RED at the 173%. this is only when 29V is showing for battery. All is perfect when normal 11-14V are being indicated.

    When at normal voltage and Cal'd the TPS is very consistent. Stays right within 1% or less with no pedal movement.

    I am going to remove the MS tonight and power on the bench.

    I am going to try to track down where the power/draw is coming from on the lights tonight.

    I forgot about the cap for the Brake but with E brake down there is no light at all through the LED.

  5. #5
    '82 T3 FABombjoy's Avatar
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    Tunerstudio -> Tools -> Calibrate Battery Voltage. What does it read?
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

  6. #6
    Senior Member
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    NorthEastJBD: I did not. It happened again about two weeks ago, where MS was rapidly switching on and off, as evidenced by the sound of a relay clicking over and over again, like there was a main power wire barely making contact and losing it again. I jiggled the wires so I could continue driving, and I haven't had the problem since, but that's clearly not a fix.

    That, and my battery light has been lighting briefly when I hit a bump. I started cleaning all the grounds on the car, but I didn't notice the jam nut behind the trailing arm bushing mounting bolt and snapped the head off. I hope to fix that this weekend, then get back to checking grounds again.

    I am theorizing the my DB39 connector on MS wasn't seated properly, but I don't have a way to know for sure, and that doesn't explain the battery light issue.

    I'm sure everything will be fine for the NERD meetup next weekend...


    I'm trying to think of what would cause the 29v reading. It almost seems like that's a fault in MS, where the top end of the voltage divider (or whatever it uses the get battery voltage to logic level) is at 29v, like it's an error condition or an internal short or something. But that wouldn't clear it self up by just turning it off and on again. I take it that leaving it on doesn't cause it to fix itself? Do you have to wait a bit between turning the key off and on again, or do you quickly flick it off and back on?

    -- Joe

  7. #7
    Senior Member powerline84's Avatar
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    Also you calibrate your tps yourself. Go in to tuner studio and reset your zero pedal throw and full throttle values. Technique I learned from luke is extend the values an additional 5 % on each side so the computer is allowed some slop in pedal variation

  8. #8
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    I am going to look at the battery voltage in the cal screen. when it is high (29V) and when it is normal (12V). All values in Perfect Tune have paralled the MS controller but I did not verify this with the battery voltage.

    I was able to cal the TPS even when the voltage was 29V but had to redo it after the reading went back to normal 12V. I don't do it again.

    Leaving a bit of leeway on the TPS makes sense & I do adjust it on the lower end.

    My car was acting like you had mentioned with it just tripping out the other day. I did read where some of the isolation areas for the drive circuits can be tighter than they should be so when I pull apart & test on bench I will be reviewing those areas.

    I did not wait between on & off of key switch. Maybe 5-10 seconds. Last night it came up 29V 2 times then was back to 12V the 3rd time. I did not have time to let the car fully warm up but at that time it did not try to cut out.

  9. #9
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    I am hoping I found it but time will tell.

    The system outputs are sinking circuit so power is always connected.

    I found that I connected the turbo blow off valves in the rear bumper to the battery power already in the bumper. This power was leaching back through the MS3 to the dash resulting in a voltage in the MS3, dash lights . . .

    I had a couple of spare wires through the feedthrough & to the rear bumper which I use for turbo solenoid power.

    So there is no more low lights in dash and voltage on MS3. I started a few times and warmed engine up.

    fingers crossed.

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