92 mtx backfiring, no start

Discussion in 'Gen 1 & 2 - Engine, Exhaust, Drive Line & AC syste' started by Doug Flutie, May 18, 2019.

  1. Doug Flutie

    Doug Flutie New Member

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    92 mtx, new timing belt, cps, water pump, good dis module, all grounds cleaned, CKS sensor working, it's got fuel 40psi and it's got good fire.

    Yes it did run fine after everything was replaced.
    Upon initial start it will hit and run rough for a second or two then die. Any attempt to start it after that has it backfiring, sometimes through the exhaust, sometimes through the intake.

    Anyone ever experienced this?

    It acts like the timing is erratic. CPU?
     
  2. luigisho

    luigisho SHO Member

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    You got codes stored? Check that first. I would look at spark wire routing, vacuum leaks, and maybe timing belt slipped. Codes first.
     
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  3. Irish Pride

    Irish Pride Irish Inside Staff Member Super Moderators

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    How long ago was everything replaced and how long before it started to backfire?
     
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  4. luigisho

    luigisho SHO Member

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    Yes. I was assuming it was in a very short time but that's an important piece of info to solve the issue.
     
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  5. tracy_s_1993_atx

    tracy_s_1993_atx SHO Member

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    My '93 ATX did the same thing. I had all these weird codes set and finally diagnosed to be the Ignition Control Module(ICM).
     
  6. FastCAD

    FastCAD Member

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    Did you verify that the cam(s) marks were aligned when you put the new belt on?
    Joe
     
  7. Doug Flutie

    Doug Flutie New Member

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    It's giving me two codes a 211 and a 452.

    Correct me of I'm wrong....
    211 PIP which is the CKS
    452 is the speed sensor

    If the CKS isn't working I won't be getting any fire correct?
    I got fire.
    Everything suggests that the CKS is either good or it's bad. No working intermittently.

    Not sure about the speed sensor code.
     
  8. BaySHO Performance

    BaySHO Performance SHO Member

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    I assume that it ran fine for a while, but is now acting up?

    The 211 is a bit of a mystery, as it's obvious that the CPS (CKS) is sending a signal, otherwise the plugs wouldn't fire. The WP can't be leaking on to it.

    My main theory is that there's water in the plug wells. Is that a possibility?
     
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  9. FastCAD

    FastCAD Member

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    I thought CKS was cam sensor?
    A bad cam sensor or connection will allow the engine to fire and backfire and die.
    Joe
     
  10. Rotor

    Rotor New Member

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    74ADE5D5-D307-46D4-9162-E6BF69327472.png From another thread.
    With the codes you’re getting this may be worth having a look at.

    I wouldn’t rule out vacuum leaks either. Had a 88 F250 that suddenly started running rough and cracking off these (literally) gunshot loud backfires. Was nothing more than a vacuum hose that had come off some module on the firewall. I don’t remember the details but the thing was critical to the timing advance if I’m not mistaken.

    A breakout box is practically mandatory if you’re trying to diagnose some if the things these cars can put you through. Good Luck!
     
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  11. Doug Flutie

    Doug Flutie New Member

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    Nah the water pump isn't leaking and there isn't anything in the plug wells. I'm not sure how I'd even get water in the plug wells

    I'll double check all the connections and vacuum lines. At this point I'm open to any suggestions.
     
  12. luigisho

    luigisho SHO Member

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    You can get water in there from washing the engine among other strange things. We still don't know how long from when you did the work to when the issues appeared.
     
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  13. Doug Flutie

    Doug Flutie New Member

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    Yeah these things are finicky enough with crap connectors, sensors, and wiring.
    Introducing water unnecessarily to the engine compartment is the last thing I would do.

    Speaking of which I'm pretty sure I figured out what was wrong.

    The CPS connector was bad.

    What I now know for sure.
    With the CKS unhooked there is no fire but tach still works.
    With the CPS unhooked the tach doesn't work and it will still fire and may or may not start and run.
    At one point the CEL came on with these codes 211, 214, 542, 452.

    And now the AC isn't working.
     
  14. FastCAD

    FastCAD Member

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    Something doesn't sound right.
    If the CPS (crank position sensor) is unhooked the engine will "not" fire. It will only crank.
    If the CKS (cam position sensor) is unhooked and the engine will not fire how do you know the tach works?
    With the a/c switch on and the ignition on does the engine cooling fan come on?
    When you turn the ignition on do you hear the fuel pump come on?
    All of these things are controlled by the CCRM (computer controlled relay module) located under the radiator cover (drivers side).
    Did you disconnect the battery negative cable before you did your service?
    The CCRM is prone to being shorted this way and the computer too.
    Good Luck.
     
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  15. Doug Flutie

    Doug Flutie New Member

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    CPS is cam
    CKS is crank

    Go unhook your CPS and try starting it while you watch your tach.

    As for the ac, when the compressor kicks on both the high and low pressure sides drop.
    So it cycles for a couple seconds at a time.
    Yes it’s fully charged.
    The guy I got it from said he just had the compressor replaced. It does look new, nice and clean with legible labels.
    It has been converted to 134.
    I’m thinking maybe a blockage somewhere.
     
  16. FastCAD

    FastCAD Member

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    Thanks for the CKS (crank) clarification.
    So you fixed the CPS connector wiring and the SHO is now running and the tach works?
    The a/c clutch does engage? Any air flow in cabin?
     
  17. FastCAD

    FastCAD Member

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    The a/c recycle switch for 134a and 22r are different values.
    Same goes for the orifice tube in the liquid line under the battery.
     

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