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General Bad CAS? (don't think so) Blown ECU... maybe!

Posted by 4pistons, Mar 29, 2020

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  1. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    91 GSX, 6 bolt, stock cams, head, engine. Stock ECU with TMO chip...I've had it for 22 years so I'm familiar with DSM's and not a newbie.
    My car doesn't have a fuel pump connector on the harness in the engine compartment that I can find. I was thinking I had a fuel pressure issue so I searched for one. Found a connector and put 12 volts to it. WHOOPS! That was the tach signal connector! Since then the car ran but breaks up getting into boost. Then I got a 23 error code "Top Dead Center Sensor" (Cam Angle Sensor). Car still ran, I drove it around but ordered a new CAS.

    2 weeks later... Put the new one in, it started right up. I warmed it up, adjusted the timing to 5* btdc, drove it around the block. All was good. Left it running then went to get gas 1 mile away boosted to 18# and it ran good. Shut off at the station. Wouldn't start back up. It would run very rough and then die in 2 seconds then flash 23 again. Swapped the old CAS in the parking lot cuz I had it with me, and still no start. Had it Towed 1 mile back. Car sat for a week. Then I did the CAS check where you remove the CAS but leave it plugged in, pulled the spark plugs, clicked ignition to ON, and spun the CAS by hand...all spark plugs lit up! Did the same with the old CAS...all spark plugs lit up! They both seemed good.

    Put the engine to TDC, reinstalled the new CAS, and it fired right up idling smoothly. I let it warm up maybe 10 minutes and reset timing to 5* btdc. Idles great. Blipped the throttle a couple times no problem. EXCELLENT!. Shut it off to disconnect the timing light and timing jumper. Time for a test drive. NO START!!! Same f'ing thing... runs rough for 2 seconds and then dies, then flashes 23 again. sh**. Disconnect battery to clear the code and try again. NOPE. No start, code 23 still.

    What did I do?? Did I short/blow the ECU when I powered the Tach Signal Connector with 12V? It's only supposed to be a 5V output from the ECU. If I did then why did it run fine twice until it was shut off?
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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  2. iugrad92turbo

    iugrad92turbo Supporting Member

    10,546
    437
    Joined May 22, 2007
    Kalamazoo, Michigan
    Pull ecu out and see if its damaged anywhere, its a 28 year old car ors so anything can happen at any given time, keep that in mind. Intemintent issues can come from any above replaced or related, I learned new doesn't always means good especially with electronics, just something to ponder, check harness for anything suspect, or unusual any frayed or damaged wires, and inspect the cas connector for damage it becomes hard and brittle and can cause issues.
     

    7K  5

    1992 Eagle Talon TSi
    awd · manual · 1G DSM
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  3. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    Mine was a mess, along with the injector wires, but I changed them all about 2 years ago.

    cas2.jpg

    cas.jpg
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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    iugrad92turbo likes this.
  4. motomattx

    motomattx Proven Member

    2,273
    918
    Joined Dec 9, 2010
    wampum, Pennsylvania
    The car is losing its camshaft reference (its intermittent), the car has it for a second when it starts but loses it at some point when running, which is flagging that code, the car doesn't need the cam signal once the car is running to stay running, but it does need it to start up which is why it wont restart once its shut off if its not getting the cam signal, the spark plugs firing doesn't prove that the camshaft part of the cas output is there, just that it has a crankshaft output signal that's working, you need to track down why your cam signal is intermittent, maybe you damaged the power transistor.
     

    Drag Race Build 3K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  5. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    Makes sense.... Is the power transistor in the ECU or does the power for the cam signal come from elsewhere?
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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  6. steve

    steve DSM Wiseman

    12,840
    613
    Joined Feb 3, 2002
    Boulder, Colorado
    The power transistor is bolted to the intake manifold just below the coils.
    The CAS (on a 1G generates both the Cam and Crank position signals) pulls a bias voltage from the ECU to ground to generate the signals. The ECU senses that change.

    With the ECU turned on and the CAS connector disconnected you should see +12, GND, and two other voltages (can't remember if it's +5 or +12) on the crank and cam signal wires referenced to ground.
     

    4K  0

    1991 Mitsubishi Eclipse GSX
    manual · 1G DSM
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    4pistons likes this.
  7. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    I just did that test as shown in the FSM. Continuity good on the ground, System voltage is 12v, 4.98v on the other two pins. I swapped the power transistor with another I had and got the same results.
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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  8. motomattx

    motomattx Proven Member

    2,273
    918
    Joined Dec 9, 2010
    wampum, Pennsylvania
    Just some random thinking here but the optical cas can act up if oil leaks past the shaft into the interior of the cas itself, you might pull the lid off and see if it has oil intrusion.
     

    Drag Race Build 3K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  9. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    Well I replaced the original with a black top and it still happened. I tested both and they both passed. I just took apart the original, which has 207,000 miles on it. It did have some leaking but nothing on the wheel or the optical sensor. I'm going to clean it up and keep it for a spare. It's looking more and more like it's an ECU issue as nothing else seems to be faulty. I have no way to test it myself. I'm gonna have to send it to ECMtuning and wait.
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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  10. 4pistons

    4pistons Proven Member

    607
    24
    Joined Nov 13, 2002
    Port Charlotte, Florida
    UPDATE: Not solved! I bought another 1G Turbo ECM, plugged it in and it started. I let it warm up for 5-10 minutes and shut it off. Re-started it. No problem. Backed it out of the garage. Shut it off again and re-started it. Drove around the block, shut it off and restarted it. Went for a drive and it drove fine, revved, boosted (although by now I turned the boost way down) seemed normal. Drove about 20 miles. Pulled back in the garage, shut it off and re-started it. All good. Yay!

    Car sat about a week. Went to start it and NO START. Shaking and sputtering and dies. Flashing Code 23 again. So far I've checked the pinouts at the connector, installed a new CAS, verified the CAS function, and swapped the ECU, and still have the same issue, which I've never had before. Prior to this (read my original post) the car ran beautifully. In the 22 years I've owned the car I've run into almost every DSM problem out there but this one has me stumped.
     

    2K  1

    1991 Mitsubishi Eclipse GSX
    12.400 @ 111.400 · 1G DSM
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  11. pauleyman

    pauleyman DSM Wiseman

    5,360
    1,153
    Joined Nov 19, 2011
    oklahoma city, Oklahoma
    Have you checked the harness at the cas while the car is running? Wiggle it around and see if a wire is making poor cinnection.
     

    Street Build 3K  1

    1997 Eagle Talon TSi AWD
    awd · manual · 2G DSM
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