still can't get rid of misfire!

Discussion in 'SN95 4.6L Mustang Tech' started by stangGT97, Mar 30, 2006.

  1. well, I don't have a friend at a dealer, but I guess I could take a ride over to the one nearby and ask if they do that. Do you think I should take the car to autozone to get the coil packs tested first, assuming they can do that there? Sorry if this is getting annoying to you guys...
  2. I've been really busy lately and haven't been able to get to the dealership for a compression test because it is about a 1/2 hour away from me. However, I did get my hands on a multimeter and took 10 minutes to test the coil pack resistances, both primary and secondary. Here are the results (rounded)-

    Primary - Haynes manual specifies about 0.3 to 1.0 ohms
    Drivers side - 0.9ohm
    Passenger side - 0.8ohm

    Secondary - Haynes specifies a 6.5 to 11.5k-ohm
    7/4 - 12.52ohm
    6/1 - 12.6ohm
    5/3 - ~12.5ohm
    8/2 - ~12.4 ohm

    As can be seen, the primary resistances all checked out, but the secondaries were all over 1000 ohms too high. I'm begining to think that this is probably the cause of the misfire. I know that the fine-wire plugs that I installed (motorcraft replacements) require less voltage to produce a good spark because the electrode is thinner - installing them did make the car run better but did not completely eliminate the misfire. This leads me to believe it is a coilpack output voltage problem that is making the car misfire under load, which is seemingly reinforced by the resistance measurements I took. Also, a CEL was never triggered because the misfire is not too violent, just I know its there and it is very annoying.

    What do you all think? Thanks all!! :SNSign:
  3. where do you live.. are you in eartern mass?

    now remember fuel can wash down the rings in a cylinder that is misfiring and that can cause a compression drop, so just because a cylinder is down compression wise does not mean it's a valve problem
  4. yeah mike, I'm from Reading, but am currently in Amherst at UMass. The nearest dealership is Northampton Ford which takes about 20 minutes to get to without traffic, 30+ with traffic. I've been busy figuring out summer co-ops in my major and doing hw until 4 am, so the only thing I've been able to do was the resistance check.

    I took your advice a couple weeks ago and did an oil change and cleaned the plugs, but even with uncontaminated oil and unfouled plugs the misfire was still there. Then replacing the plugs with AGSF-32FM-F4 motorcraft plugs helped the car power wise, but it still misfires under load @ low revs (<2000rpm)

  5. too bad your out in amherst. I was going to tell you to bring your car down to my work and I would take a look at it for you. I work at a ford dealer that will remain nameless ( because ford reads this forum and just in case they don't like something I have to say, they don't need to know where I work)

    my dealer is in the waltham/watertown/newton/needham area. one of the 3 located there. :)
  6. cool man, I really appreciate the offer! I will PM you the next time I am back that way, which will hopefully be sometime soon. My dad works in Waltham, thats about 20 min from my house. Cool, I get to meet a fellow stangnetter... and you get to meet my POS car haha.

  7. LOL ok PM me when you think you will be able to bring it out to me.
  8. ok man sounds good. thanks for all the help!
  9. hey man have you figured out the problem? I'm having similar issues with my car still
  10. well, honestly I don't think I've completely cured the problem, but the car seems to be running a little better after putting in OE Motorcraft plugs. I will be getting compression tested as soon as I can make it home, and then if that checks out, its probably the coil packs. I was hoping someone could give me some insight about the resistance readings I took on the CPs but so far no one has replied about them... lemme relist

    Secondary resistances (Haynes recommends <11.5kohm
    -All resistances were 12.5kohm and greater

    Is that a problem?
  11. Ok I think I managed to fix the misfire. Me and a buddy put on new Motorcraft 8mm wires and seafoamed. The plugs are new Motorcraft plats. We also found a good amount of corrosion on one connection on the passenger side coil pack, which we cleaned out. The car seems to run better, I didn't feel the misfire, and the exhaust isn't popping as much any more. Hopefully this completely cured it. Thanks again for all your help!
  12. Thanks for the update! Glad to hear it's running better! :nice:
  13. oh yeah I am relieved too, I was ready to take this thing out behind the shed and put 'er down :)
  14. damn!.....
  15. well now that this thread has been bumped up, I might as well give another update. The car started missing again, so I installed Accel coilpacks, but it still does it. The car pulls great through the rpm range, but down low at light throttle it will still buck.... so annoying
  16. I had same problem while back too. Turned out to be bad wires at first. Then the alternator.
  17. Not an obvious choice but how is the battery and alternator?
    Take it to a Walmart TLE they will test the system for free.
    I have seen this cause strange problems.
    Also remove the ground on the drivers side of the engine/chassis and give it a good clean, hell give every ground you can find a good clean removing corrosion re-attach the ground and paint over to ensure a good connection.

  18. well everything in the ignition system is brand new - plugs, wires, coil packs. The alternator is the original, and I do notice sometimes that it seems my charge is a little on the low side even with the car on. Maybe thats what it is. svttech suggested a leakdown test, but now that I've moved to Ohio I have no idea where I can get one.

  19. ok man I will take a look at my connections later today. thanks!