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Thread: Misfire after plug change, need expert help please!

  1. #1
    Join Date
    Dec 2004
    Posts
    61

    Exclamation Misfire after plug change, need expert help please!

    Hello all, I appreciate any help you can give me, this quote is from my previous thread titled "Hesitation at WOT". I decided to start another thread, because I'm not really diagnosing a WOT problem anymore, it's just a general misfiring going on.

    When I am in idle, the car will misfire here and there, dropping down to 600rpms or so. When I rev it up it runs fine, but if I try to put it in gear at all it's immediately chugging out. Vac pressure at idle is approx 18psi, and drops to 17psi when misfire happens.

    Just to clarify again:

    All plugs are brand new NGK G-Power. Fuel filter is new. And wires have been replaced with Beldon Premium wires.


    UPDATE OF WORK DONE:

    Today we tested the wires coming from the DIS thanks to a helpful 11pg posting called "Weird ____ - Experts Help" (Can't remember exactly).

    The DIS seemed to be acting normal AFAIK. With key in "on" position, ground pin (7) on the DIS read 12V so it's good. Pins 8,9 and 11 all read 9.37 on the automatic setting of my multimeter. Turned the car on and probed the same wires with a test lamp. Light blinked normally on all wires, even when car was chugging out. Turned the car off.

    The DIS seemed like it was just fine, so we moved on to check the resistance in the coils. In the other thread they said to test them as pairs:

    A B C
    A B C

    Like so. The ohm readings are as follows:

    A = 14.11
    B = 14.22
    C = 14.16

    I assume that is close enough to being normal? So can anyone make some sense of that, or does it help narrow it down any? I just thought I may as well check while I'm waiting for the wires to come in.

    Thank you all again for your continued help, the people in the thunderbird/cougar communities are one of a kind.

    -Derek
    So I have now changed wires and plugs, and tested DIS and Coil. What else could be doing this?? Can anyone tell me if the readings I received are normal? Anyone have any other ideas? Alternator? I've had to change the battery out and charge it a couple of times over the last couple weeks while diagnosing some other problems, but I figured that would just be from not driving it.

    I'm planning on heading out of town with the car on thursday, so I would appreciate any help! This was just supposed to be an easy sparg plug change

    Thanks in advance,

    -Derek

  2. #2
    Join Date
    Oct 2004
    Location
    Charlotte, NC
    Posts
    8,159
    Did you remove your IC tubes to install the DS plugs....

    You also might have cracked one of the plugs while installing it......

  3. #3
    Join Date
    Dec 2004
    Posts
    61
    Sorry can you clarify: What are IC tubes?

    I'm aware that I could have cracked a plug, in fact, I already replaced two that I thought MAY have made a sound while istalling them, but it still did the same thing. I'm sure it could be any of them now, but I would like to think that's ruled out. I also checked for any wiggle or wobble while installing the new wires, and found nothing. Not a perfect check I know, but I would like to hope I don't have to go buy 6 new plugs again and do the whole thing over.

    Thanks for the suggestion on the IC tube thing, I Don't believe I removed anything on the Drivers side to get at the plugs, I went from underneath.

    Thanks agian.
    -Derek

  4. #4
    Join Date
    Oct 2004
    Location
    Charlotte, NC
    Posts
    8,159
    The IC tubes are the tubes that go to and from the intercooler next to your radiator....

    They can sometimes develope a leak and cause all sorts of problems.....

  5. #5
    Join Date
    Dec 2004
    Posts
    61
    Argh- Intercooler! I knew I'd feel like a dummy, sorry I learn as I go here.

    I'll give those a check, is it best to just buy some brake/carb cleaner to check for any vac leaks while the car is on?

    Thanks
    -Derek

  6. #6
    Join Date
    Dec 2004
    Posts
    61
    one more thing... Something crazy had happened..

    Could this be contributing to my problem??

    After we first changed the plugs... we took it for a drive and it was acting pretty normal, only slight hesitation around 9-10 Psi of boost (Hence the reason for my previous post). On the way home, got some chugging and then all of a sudden car went CRAZY! Tac and guages were bouncing up and down, lost all power to the engine, buzzers going off etc. Pulled over, Tried to start, and nothing. Looked under hood and realized one of the connectors to the DIS had popped off. plugged it back in, and car started up (running rough). I limped home, and I've had this misfiring problem ever since. Anyone think I may have somehow shorted out the DIS? These readings I got from the wires at the DIS were after the problem, so it looks like it's still doing it's thing.

    Also, big-e, if you meant the metal intercooler tubes, I never touched them, but thanks for the suggestion.

  7. #7
    Join Date
    Oct 2004
    Location
    Charlotte, NC
    Posts
    8,159
    Sounds like she is posessed.....

  8. #8
    Join Date
    Dec 2004
    Posts
    61
    Does "possessed" show up on a code reader? Is there a way to fix this "possessed"?

    Haha, thanks for trying. Anyone else? I am worried I'm going to have to re-insure my 94 3.8L NA Cougar and put it back on the road, blech!

  9. #9
    Join Date
    Jun 2008
    Posts
    240
    I would just go and buy another DIS. If the problem does not go away then remove and replace with the old one and get your money back.

  10. #10
    Join Date
    Apr 2002
    Location
    Norcross, GA
    Posts
    3,303
    Make sure none of the cable bundles are rubbing on one of the belts and cutting into a wire. Once that made mine go berzerk till I found it and got the cable tucked out of the way. ESD, static electric discharge off of the spinning belt. If the engine was running or ignition on when you reconnected the DIS plug, it indeed could have zapped the DIS. Always shut off the power when unplugging and plugging electronic modules.
    90 5spd, best ever E.T. 12.250
    best ever 1/4mi speed 112.89 mph
    Current dyno tune 383.54 rwhp 418.88 rwt

  11. #11
    Join Date
    Dec 2004
    Posts
    61

    Update

    So I got a quote on a new DIS from Fraud... Ahem... I mean Ford.

    They want over $600 plus shipping for the DIS....

    So that is definitely not an option. Can anyone help with the values I got from my multimeter?

    Thanks
    -Derek

  12. #12
    Join Date
    Dec 2007
    Location
    Salem, OR
    Posts
    6,340
    The OHMS you show for the coil are a bit higher than what I've seen: 13.59~.67 - in any case, you can have issues with a coil that may not show when testing. Can you get your hands on a known good coil and try it instead?

    Test the DIS for shorts to ground...pull both plugs and check all pins. Only one pin, #7 I believe, should connect to ground. If you find others, the ground path transistors may be fried. Autozone, etc. should want around $200 for a fresh one. You might find an auto parts store willing to test yours as well.
    Last edited by KMT; 08-18-2008 at 06:03 PM.

  13. #13
    Join Date
    Apr 2008
    Location
    Newport Mn
    Posts
    84
    Just a thought... I used my Chiltons manual to reference the firing order of the coil pack when putting my engine back together. I put new plugs, wires, coil pack, etc so I was relatively sure everything was good, yet it still started hard and ran rough. Turns out the firing order listed in my Chiltons for my engine was wrong. I switched the wires around on the coil and the engine started and ran like a dream. Even with half the engine firing at the wrong time, it still started and ran, just not well. It's an easy check before you start looking at the sensors.

  14. #14
    Join Date
    Oct 2004
    Location
    Metro Denver Area
    Posts
    2,514
    You know the tach jumping all over is a symptom of cam sensor issues. Take a look there and make sure none of your wires are stretched\damaged.

    Best of luck

    -Bryce






    Quote Originally Posted by Cougarfetish View Post
    one more thing... Something crazy had happened..

    Could this be contributing to my problem??

    After we first changed the plugs... we took it for a drive and it was acting pretty normal, only slight hesitation around 9-10 Psi of boost (Hence the reason for my previous post). On the way home, got some chugging and then all of a sudden car went CRAZY! Tac and guages were bouncing up and down, lost all power to the engine, buzzers going off etc. Pulled over, Tried to start, and nothing. Looked under hood and realized one of the connectors to the DIS had popped off. plugged it back in, and car started up (running rough). I limped home, and I've had this misfiring problem ever since. Anyone think I may have somehow shorted out the DIS? These readings I got from the wires at the DIS were after the problem, so it looks like it's still doing it's thing.

    Also, big-e, if you meant the metal intercooler tubes, I never touched them, but thanks for the suggestion.

  15. #15
    Join Date
    Dec 2004
    Posts
    61
    Ok thanks for the suggestions, I'll re-double-triple check the firing order to another diagram, and I'll get my buddy to snoop around the cam sensor and see if we find anything.

    All wires on Dis previously tested ok, and the #7 pin was a solid ground, even when we tried to shake around the DIS to cause a short.

    Thanks again!

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