91 MTX, tachometer stopped working, engine ruining rough

Discussion in 'Gen 1 & 2 - Emergency Issues - Help & Maintenance' started by Levi Brion, Jan 10, 2019.

  1. Levi Brion

    Levi Brion New Member

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    I accidentally redlined my 91 mtx trying to merge and now my tachometer reads zero and the engine runs a little rough cause the car to shake a little bit. Any info will help.
     
  2. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    Several possibilities here. In some cases the tach can be physically damaged by what happened. In some cases the cam sensor is bad causing the tach not to read. In some cases the wiring or pcm is the culprit. It may be related to the over-rev or it may be coincidence.

    Please read the codes and let us know what you find.
     
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  3. Levi Brion

    Levi Brion New Member

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    73, 74, 52. Engine definitely feels less powerful too.
     
  4. SHOdded

    SHOdded SHO Member Supporting Member

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  5. luigisho

    luigisho SHO Member

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    Those are all possible operator error codes during self test. I agree with checking the cam sensor. I would clean the MAF and pull the plugs and take a look.
     
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  6. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    Those codes are all operator errors during the key on engine running test. Please pull the codes with the key on engine off test, and report those.
     
  7. Levi Brion

    Levi Brion New Member

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    14 and 19 for engine off test
     
  8. luigisho

    luigisho SHO Member

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    Possible cam sensor or something else in the electronic ignition system like maybe the PCM is damaged.

    I would try a cam sensor replacement and go from there.
     
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  9. Levi Brion

    Levi Brion New Member

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    So this is the cam sensor?
     

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  10. blk\blk90

    blk\blk90 SHO Member

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    Yes. It's on the pass side of the motor on the rear cam shaft. It's tough to get at, but there are writeups on here.

    20181020_221251.jpg


    20181020_221309.jpg
     
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  11. zoomlater

    zoomlater SHO Member Supporting Member

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    If you find oil in there, you should replace the cam seal as well
     
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  12. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    So it is complaining of erratic signals from both the crank sensor and the cam sensor. I would reset codes and see if they come back in a couple days. If both of those come back, I would replace both cam and crank sensors. However, I have seen some of these cars in recent years where the issue was really in the wiring or the pcm when those codes appeared, so there is no guarantee that the sensors will fix the issues.
     
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  13. Levi Brion

    Levi Brion New Member

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    So this morning when I went to start my car it barely started and would cut off right after. It is about 40 degrees, so I'm not sure if it was just a combination of the cold and the problem that was from last night or if the problem got worse. I will try to replace the cam sensor today and see if that helps.
     
  14. Levi Brion

    Levi Brion New Member

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    I think I smell gas when the engine is running now.
     
  15. luigisho

    luigisho SHO Member

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    Well that is unignited fuel most likely. The ignition and timing is suspect. So electronic or maybe mechanical. You need to check your timing. It could be off a tooth now
     
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  16. Levi Brion

    Levi Brion New Member

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    How do I check the timing? Is there a link to this?
     
  17. luigisho

    luigisho SHO Member

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  18. rubydist

    rubydist SHO Master Staff Member Super Moderators

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    I would not worry about the timing now. That will affect power levels, but it will run okay. You have other much higher priority issues to resolve first.
     
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  19. BaySHO Performance

    BaySHO Performance SHO Member

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    OK, so 14 points to the CPS, 19 points to the cam sensor. If the CPS was permanently bad, there wouldn't be any spark and the car wouldn't start, which isn't what's happening. Seeing as the tach goes to zero with a bad cam sensor, and the car sometimes runs rough, change the cam sensor. In emergencies, if you can get the car started and running smoothly, the cam sensor has done its job and correctly identified the cylinders (CID). Unplug the sensor while the engine is still running. It should continue to run smoothly under those circumstances.

    There's an outside chance that the tach still doesn't move even with a new sensor. If so, look closely at the gauge. You will see a little pin at zero RPM. Is the needle stuck on the wrong side of the pin, preventing it from moving? If so, warm up the engine, then go WOT. Hold it there until the tach needle rotates anticlockwise and finishes up on the right side of the pin. Should only take a couple of seconds. Always works if done right.
     
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  20. Levi Brion

    Levi Brion New Member

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    Issue solved. Went through some of the connections to the various sensors and she fired right up. The real question now is where to start with upgrades!

    Sent from my SM-G950U using Tapatalk
     

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