2000 Seville constant misfires on cylinders 5 and 8, what is common here?
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 2000 Seville constant misfires on cylinders 5 and 8, what is common here? in Past Cadillac Vehicle Discussion; First of all, I've been browsing the forums for a while but never had the need to post until now. ...
  1. #1
    HookFade is offline Cadillac Owners Member
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    2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    First of all, I've been browsing the forums for a while but never had the need to post until now. So I appreciate all the information on the boards...but now I'm at a point where I bought this car because another mechanic friend couldn't fix it, and now I'm lost.

    I'm able to monitor the individual cylinders on my OTC scanner. Cylinders 5 and 8 misfire constantly from the time you start the car till you shut it down. Cylinders 2 and 3 will misfire while driving or revving, but never at idle. Despite all this the car drives pretty smooth still. The engine light will not flash until you start driving around 10mph and on.

    I have tried the following, swapping coils front to back, changing coils from another car, changed plugs, changed boots, misfire never moves. Checked both injector fuses and are ok, all injectors ohm out the same at like 13.6 I think. I have not yet checked the voltage at each injector yet. All that was found to be abnormal was on cylinder 3 there was some rust and corrosion on the spark plug and the tip of the coil, thought I had it nailed there but it made no difference whatsoever.

    Looking at the wiring diagram, I can't find anything common between cylinder 5 and 8 that would make them misfire at the exact same time, all the time. are they on the same driver in the PCM? I really don't know, I'm a VW/Audi guy just wanting a Caddy to drive. 5 and 8 are next to each other in the PCM it looks like, but do they fire together? I will post a pic of the PCM diagram.

    The car does not smoke, does not use oil, does not lose coolant. It drives like a car with a skip, not like a car with 4 misfires. Its really strange to me.

    The only code in there is the P0300 random misfire that everybody gets. There are some history codes related to the EGR, which I was going to look into but I held off because I don't think that will help with these 2 cylinders misfiring.

    Any ideas will be appreciated and carried out and I'll post my results to add to the great information this place offers.

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  3. #2
    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Injectors.JPG

    Tried to upload this screenshot of the injector diagram but I can't get the whole thing on there
    Attached Images

  4. #3
    JimD is offline Cadillac Owners Connoisseur
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Quote Originally Posted by HookFade View Post
    .... I have not yet checked the voltage at each injector yet.
    That should be your next step.

    With KEY ON, stick your voltmeter positive test lead in pin A of the injector connector for cylinders 2, 3, 5 and 8 with the meter negative test lead on a good chassis ground point. You should see battery voltage. Wiggle and bend the injector wire harness and see if the voltage remains steady.

    Had a poster some time ago with 0 volts to one injector and situatiion was repaired by jumping the voltage from another injector on the same fuse, pink to pink.

  5. #4
    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Simple enough, I'll try it tomorrow and let you know. Thanks

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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Cylinders 2-3-5-8 are each 180° apart in the firing order - in your engine, same coil/injector trigger sequence.

    1 - 2 - 7 - 3 - 4 - 5 - 6 - 8

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    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Since the covers are already off I decided to run out and check and unfortunately I have battery voltage on all 8 injectors. Key on engine off. Next I can grab a noid light which I don't have here... Other than that Im out of ideas

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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Injectors "fire" as the PCM completes a ground to each in the proper firing/timing order.

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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Have you cleaned the TB lately? If not, you might give that a try.

  10. #9
    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Have not, but before I started working on the car someone had done the intake gaskets and plenum boot cchasing this issue so I'd imagine they would have cleaned it but I can always look. Are PCMs ever bad on these? That's the only thing I really can come up with that could affect individual cylinders like this

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    JimD is offline Cadillac Owners Connoisseur
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Quote Originally Posted by HookFade View Post
    ....Are PCMs ever bad on these? That's the only thing I really can come up with that could affect individual cylinders like this
    Any module can fail at anytime. But reported PCM failures are rare, bordering on non-existent.

    It would be worth your time/effort to inspect the connectors at your PCM looking for oxidation/corrosion/wire harness damage. Remove whatever engine air intake pieces are necessary to gain access to the area in front of the air filter. Your PCM is located in that air flow path upstream of the filter.

  12. #11
    crezzy2k1 is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Quote Originally Posted by JimD View Post
    Any module can fail at anytime. But reported PCM failures are rare, bordering on non-existent.
    Mine was doing something very similar to what OP has posted and it turned out to be the PCM.

    OP Check all your injectors are firing, should be constant click,click,click from all of them, if not check the wiring, if thats good you MAY have a bad PCM.

  13. #12
    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Ok so I just put a noid light to each injector connector individually, all blinking and at the same rate so nothing found there either. The idle changed with each injector that I unplugged which I thought was also strange, I figured the bad cylinders wouldn't have much of a change. I can't hear audible clicks from the injectors but that doesn't mean it isn't happening, just not sure if I'm hearing it. I will check for corrosion at the PCM connector tomorrow night when I get back to the shop.

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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Misfire under load would equal weak spark or incorrect timing, couple things come to mind. Bad/missing icm ground wire, non delco plugs or poor positive connection.
    Does your scanner monitor timing and injector pulse time?
    Trying to think if your car is getting incorrect sensor readings and it's throwing off the timing/injector pulses.
    I've had a couple cars sensors go bad but at a reading that was good and vehicle never knew it and only found by scanning real time.

  15. #14
    HookFade is offline Cadillac Owners Member
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Quote Originally Posted by rodnok01 View Post
    Misfire under load would equal weak spark or incorrect timing, couple things come to mind. Bad/missing icm ground wire, non delco plugs or poor positive connection.
    Does your scanner monitor timing and injector pulse time?
    Trying to think if your car is getting incorrect sensor readings and it's throwing off the timing/injector pulses.
    I've had a couple cars sensors go bad but at a reading that was good and vehicle never knew it and only found by scanning real time.
    I'll try all of those things but what do you mean, poor positive connection to what? The PCM? Or ICM(Ignition module I assume?) I thought each cassette had its own module, but I have misfires on separate sides. I'm open to anything though, I'll check everything.

    The scanner is an OTC Genesys so I can read out most engine values, I'll check on the timing and injector pulse time. Are you talking cam or crank sensors giving incorrect readings?

    I'm still nowhere on this car its blowing my mind.

  16. #15
    Submariner409's Avatar
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    Re: 2000 Seville constant misfires on cylinders 5 and 8, what is common here?

    Yes, each cassette has its own removable ICM and they are identical.

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