Tach needle bouncing effected by gas pedal, effectiing auto tranny.

Short Description: Tach needle bounces around but the engine revs stay normal. While driving on the freeway pressing the gas pedal causes the tach to jump around or just go to zero. As soon as I let off the gas the tach goes back to normal, press the gas and it freaks out or flat lines. All while the engine is running normal. Recently when the tach starts to flip out the tranny will jump from 4th the 3rd a bunch like it can't decide what gear to be in. This can sometimes be helped by switching from Drive to Sport and manually selecting 3rd or 4th.
Here's a video of it happening.

http://youtu.be/z57fW8Pcmig

More Info:
The tach flutter has been happening for some time now, but it used to come and go and had no effect on the drivability of the car. It seems to have gotten progressively worse, and is effecting more things. Other things to note are that my tranny is having a harder and harder time selecting park. I can shift into park fine but it takes a few seconds for the car to realize it's in park and for the P to light up. Also the head lights dim when I press the breaks. Don't know if any of this is related or not.

Comments

  • I would check grounds to make sure you still have solid connections under the hood and they aren't fighting through rust.

    Tach flutter could be due to a failing ignitor in the distributor.
  • LowFlyin' wrote: »
    I would check grounds to make sure you still have solid connections under the hood and they aren't fighting through rust.

    Tach flutter could be due to a failing ignitor in the distributor.


    I think the distributor is not OEM, although it is relatively new. Does a failing ignitor require a complete distributor replacement.
    I'll look over the grounds.
  • cwin13cwin13 New Wagonist
    My RT just started doing this too...in for more info
  • jasnall wrote: »
    I think the distributor is not OEM, although it is relatively new. Does a failing ignitor require a complete distributor replacement.
    I'll look over the grounds.

    The ignitor can be purchased separately and replaced if you don't mind taking the distributor apart.
  • I just had it apart, I all still looks new and shiny but that doesn't mean the ignition isn't bad I suppose.
    Where does the tach get it's signal and whats causing it to flutter around? The biggest head scratcher to me is why does the gas pedal effect it? As far as I know you push the pedal and it pulls a cable on the throttle body. So maybe the TPS or something along the way is wonky?

    edit
    Just found this today, Pretty much describes my issue. I'll look at replacing the ignition module or dizzy and report back.:
    "The problem might be with the distributor module located at the base of the distributor. This module is an input to both the tachometer and the engine management computer. When these modules malfunction, it can cause the tachometer to act eratic. The computer then loses this input signal where it doesn't know where the transmission shift points should be."
  • Thanks LowFlyin', you were right. I took the ignitor module out of the dizzy and took it to Autozone to get tested, it failed on one of the leads. Picked up a new one, plopped it in and all seems good so far. I've only been on a short drive but didn't have any issues.
    It's a pretty easy fix cwin13, let me know if you need more info.
  • cwin13cwin13 New Wagonist
    just take the ignitor out and replace it? If it gets any worse I'll do that, my transmission hasn't been affected by this yet but keeping my fingers crossed
  • Yup. Open dizzy, take rotor off, take cover off, unplug 4 wires on the ignitor, undo 2 screws to pull out ignitor. The new ignitor comes with new thermal paste to use with your old heatsink off the old ignitor, it screws off too. Then put it all back together.
    One note, The tach lead wire was a little loose on mine before I removed it, It may be worthwhile to take yours apart to check the wires and stuff.
  • cwin13cwin13 New Wagonist
    good info thanks
  • cwin13cwin13 New Wagonist
    Jasnall, just wondering if replacing the ignitor fixed your problem altogether?
    Today I was driving home on the highway and the rpm gauge just dropped to 0 for a few miles and kicked back up to normal then when I was back in town idling at a red light the car just quit and i rolled it into a parking lot and tried it 3 times before it started up again. I'm thinking it's not a main relay issue cuz I hear the fuel pump kick on, so I'm just wondering if changing the ignitor helped cuz that's my next step along with cap and rotor.
  • cwin13 wrote: »
    Jasnall, just wondering if replacing the ignitor fixed your problem altogether?
    Today I was driving home on the highway and the rpm gauge just dropped to 0 for a few miles and kicked back up to normal then when I was back in town idling at a red light the car just quit and i rolled it into a parking lot and tried it 3 times before it started up again. I'm thinking it's not a main relay issue cuz I hear the fuel pump kick on, so I'm just wondering if changing the ignitor helped cuz that's my next step along with cap and rotor.

    Ya i fixed every problem I was having, my car never shut off like yours did but the tach would drop to zero like that on the freeway. My auto tranny is shifting better and smoother, the engine runs tighter, replacing it changed everything.
  • AbideAbide Council Member
    just a quick FYI the tach gets its signal from the blue wire coming out of the distributor, i assume off the ignitor.
  • cwin13cwin13 New Wagonist
    Cool thanks for the info guys, glad it's working for you Jasnall
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