Engine misfire at certain times of the day - 2003 STS - Page 2
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Northstar Engines and System Technical Discussion Discussion, Engine misfire at certain times of the day - 2003 STS in Cadillac Engine Technical Discussion; Im with ranger I think Its a heat related thing that causes some type of short in the coilpack/ ICM ...
  1. #16
    ELDO GUY's Avatar
    ELDO GUY is offline Cadillac Owners Fanatic
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    Re: Engine misfire at certain times of the day - 2003 STS

    Im with ranger I think Its a heat related thing that causes some type of short in the coilpack/ ICM system . I had a cat problem on a 82 eldo and it was way different it was clogged up and limited the speed to about 45 MPH.

  2. #17
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Quote Originally Posted by Ranger View Post
    It's possible that as it heats up the heat affects something. I've had a starter fail only when it was hot. Contacts expand and break contact.

    Everything you ever wanted to know about CAT's.
    http://www.aa1car.com/library/converter.htm
    What a great bit of information

  3. #18
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Update:

    Didn't go to lunch today in the car and had no issues whatsoever this morning when starting out and no issues when returning home, i did have about a 20 minute stop round the brother in laws and had no issues when i restarted which is usually when it'll mis-fire.

    I will update as the situation changes, thanks everyone for your input.

  4. #19
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Quick Update:

    Started the car this morning and had no issues on the way to work.
    Started the car at lunch time and it immediately started mis-firing, when we came back out and started it still was. The SES will now flash when driving along with it mis-firing and will stop and go solid as speed is increased above 30mph or so.

    Well i started the car when i left work and initially it was okay while idling and then started missing again. It was then missing at practically every stop light until i got on the highway, when i pulled up to a stop light the car seemed fine then just started missing again, it was still missing when i got home which is a first!

    I let her cool off for a while and then went and pulled the front plugs, the whole bank goes form very whitish to very darkish on a sliding scale from the ICM to the end. I had seen this the other day when i pulled them but now its much more obvious. When i pulled the rear bank a couple of days okay all the plugs were pretty much in the same condition.

    So now i'm pretty sure its guaranteed to be the coil pack.

    What a pain, i'm leaving parked up in the garage tomorrow, just so i don't ruin the CAT any further.

  5. #20
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Engine misfire at certain times of the day - 2003 STS

    Have you pulled any Diagnostic Trouble Codes from the car's built-in code reader/scanner after one of these misfire events ?

    I see the 0300 and 0420....................but, for other owners................

    The sticky thread ^^^ "How to pull codes" for your OBD2 car, write them all down and whether each is Current or History,...........and

    AWH: On-Board Diagnostic Trouble Codes (OBD2 Codes) - OBD2 Cadillac Codes

  6. #21
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Quote Originally Posted by submariner409 View Post
    Have you pulled any Diagnostic Trouble Codes from the car's built-in code reader/scanner after one of these misfire events ?

    I see the 0300 and 0420....................but, for other owners................

    The sticky thread ^^^ "How to pull codes" for your OBD2 car, write them all down and whether each is Current or History,...........and

    AWH: On-Board Diagnostic Trouble Codes (OBD2 Codes) - OBD2 Cadillac Codes
    Hi Sub. Currently the only code is P0300 Current. P0420 has not come up in quite sometime.

    Update:

    Yesterday i went back down to the garage and for shits and giggles i decided to re-check the injectors. To my amazement one of them (front bank) is not working, i think this was intermittent at first and is now permanent. I plugged the connector from the end injector onto the affected injector and it worked so no issues with the injectors. The wires on the connector look a bit squished so I'm borrowing a multimeter and will check the connector when i get home tonight.
    I have no codes for injectors at all just P0300 Current which is now obvious.

    If this ends up being the issue and if its just the connector I'm going to relieved

  7. #22
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Update

    Okay after checking the continuity of the cables for Injector 6 back to the PCM all seems good. I also checked the voltage and all is okay, the injector itself is not at fault.

    So with all that checked i started her up and all injectors were clicking away nicely, so i let her idle for 10 minutes or so then i heard the engine change tune and saw it bucking a little. So i checked out Injector 6 and it was no longer clicking, so i took the connector off and checked the voltage and i had +14V or so, so thats good, i then checked the Control cable and it was at a steady 2V or so which is bad i'm pretty sure it should be going up and down. So i then unplugged the injector next to it and tested the Voltage and Control cables, +14V and a variation in voltage as expected from the PCM cable which is correct, so i plugged that connector onto Injector 6 and it started clicking again, while i was there i plugged the connector from injector 6 onto the injector next to it and nothing. So it looks very much like the PCM has decided to call it a day on Injector 6, well after it gets a little warm!

    Has this happened to anyone before, and is there anything i should do or check before i go and find a new PCM?

  8. #23
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Just a quick note, i tested continuity back to the PCM after this had happened on Injector 6 connector and it was still good, So this isn't a loose connection, at least not in the wire.

  9. #24
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Update:

    I have replaced the ICM with no effect on the injector. This is really pointing at the PCM.

  10. #25
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    Re: Engine misfire at certain times of the day - 2003 STS

    Yuck. PCMs are pretty reliable from what I've heard, but I suppose they could fail. Check junk yards. You'll have to have a TECH II at a dealer transmit your current mileage and such over I think.

  11. #26
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Yeah i found a place online that sells them for $160 and also codes them to your specific vehicle. The only thing they can't do is the CASE re-learn which is a tech2 job.

  12. #27
    crezzy2k1 is offline Cadillac Owners Member
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    Re: Engine misfire at certain times of the day - 2003 STS

    Update:

    This has finally been fixed. It did turn out to be the PCM. Bought a used one off eBay then had a place called 'AutoSelect' perform the reprogramming. All in all cost me $165 to get it all done which considering that the PCM is over $800 at the dealer, was a bargain!

    Next repair: The steering shaft!

    Oh i should mention that the Cadillac dealer i went to in this area didn't have a clue how to re-program the PCM and told me i needed to bring the entire donor car to get it done even after i explained to him how to do it! I promptly walked out!

  13. #28
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    Re: Engine misfire at certain times of the day - 2003 STS

    Glad you got it fixed. Even more glad that you are avoiding the local dealer! They sound like a bunch of morons!

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