still can't get rid of misfire!

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

  1. hey all, I'll start by apologizing for writing so much but I am trying to be as specific as possible as I want to kill this problem once and for all.

    I've been having a misfire problem with my 97 GT for the past few months, and everything I have done has done nothing to solve the problem.

    Here are the symptoms:
    -Loss of low end power
    -No longer pulls well at the top end (used to pull decent with PI manifold on)
    -A distinct misfire under load, usually at low rpms (most notably at ~1400, but does it all the way to 2000 or so) - car shakes me a good bit
    -This may be the way mustangs are, but the idle doesn't seem very smooth as I can hear "blip" noises from the exhaust
    -Occasionally, when I stop at a light, the RPMs will drop to 500, go to 1000, and follow a sine wave of sorts for a few seconds before idling at 750.
    -There is no sign of detonation/pinging (so I don't think it is fuel pressure related)
    -Car throws no codes

    Here's what I have done to try and fix it
    -Tried new Autolite AP764s, then replaced with copper 764s
    -Changed fuel filter
    -New IAC, new DPFE (EGR controller)
    -Cleaned MAF twice with electrical contact cleaner
    -Checked all vacuum connections, tightened intake tube
    -New PCV
    -Checked torque on the intake manifold - it was fine
    -Thinking that the "misfire" feel was my clutch slipping, I had a new clutch/flywheel put in

    Possible sources:
    -Plug wires have only about 15k on them, but I was thinking they are possibly the culprit?
    -Coil packs are stock as far as I know, and unfortunately I don't know any place around here that will test them
    -Possibly a weak alternator output isn't giving enough juice to the ignition?
    -Gap is fine on plugs, but maybe the car will only work properly with Motorcraft stockers?
    -God hates my car and doesn't want me to be happy with it? haha

    Thank you all in advance for any help you can give. As you can see, I have been wrestling with this beast for some time, my mechanic says he can't feel it but I definitely can - as he explained to me, if he drove the car every day, he would know what squeaks, rattles, etc were just part of it being a 9 year old car, and what was something new/problematic. The thing that stumped him was that there was no code being thrown. Any help is greatly appreciated, and sorry again for writing a book!
  2. run a compression test on all cylinders.

    if you can bring it to a dealer and have them run a relitive compression test with the WDS. you might have a valve sealing problem.
  3. Hmm, interesting. My rpm's also seem to go up and down at a light or when coming to a stop and i hear blips form the exhaust too. I also have 47k miles and don't think the plugs have been changed so im doing that next week. If that doesn't work, then sadly i might have to take it to the dealership and see whats up. :(
  4. try wires they seem to be a problem on 4.6 trucks
  5. Mike, I will look into a compression test whenever I am back home because I trust my dealer there. Interestingly enough, this seemed to have started after I first changed my spark plugs. I was running Motorcraft double platinums for about 20k miles (2 yrs) so I replaced them with correctly gapped Autolite platinums as per recommendation of Autozone, and the car seemed to start misfiring afterwards. When I did that plug change, I did not torque cyl 8 plug enough and the car misfired pretty bad for a while, then I torqued it but the misfire remained. Then I put in regular copper Autolites, and that didn't help at all. I then tried your oil change/spark plug cleaning routine, thinking the crank case was contaminated with gas, but the misfire is still there!

    I will say this though, you know when you do something to your car, and afterwards you are 200x more attentive to every little sound and shake? I think this misfire could have been going on even before the plugs and I only really started to notice it because I was paying close attention to everything.

    Also, I had my plug wires off when I did my PI manifold change, maybe I screwed something up by doing that? Like they got moisture in them or whatever? So annoying!! Keep the suggestions coming though guys, I appreciate the help.
  6. i'm having the same issues with my car too, it hesitates when i get on it and it bucks below 2K rpm, the car really feels like a turd :( . I've changed the plugs and cleaned the MAF but it still does it. i checked the oil and it smells like gas so i'll change that during the weekend and see what happens. keep us updated if you figure it out man.
  7. yeah man it sucks! i'm still waiting to get some more advice, cuz I really think I've run out of ideas. Being that it is a DD, I really can't afford to have it at a shop for an extended period of time
  8. Compress test, then leakdown test. That will give you a lot more insight into whats going on in there...

    FWIW, check your oil for coolant (it would look milky), and check your coolant for oil (it will look, well, like ****). That will almost rule out head gasket failure.

    If you still suspect electrical problem, drop by autozone/oreillys and have them check the voltage on it in a matter of a few seconds..

  9. get the autolites out of there and get another set of motorcrafts. Don't ever listen to autozone or any other chain parts store. atleast check the numbers on the side of one of the plugs and make sure that the right plug for your car. I would not put it past the monkees at autozone to sell you the wrong plug.

    Now I am leaning toward the plugs cuasing this problem.
  10. my car was misfiring pretty bad and i put new plug wires on it and it fix it. but anouther thing that has happen to me, and i know this will sound kinda dumb but when i was changin out my plugs one of my fuel injecter got unplug:bang: and made it run like crap soo maybe check your injecters out too
  11. they are the right model number, but you think its just the fact they are Autolites and not Motorcrafts? I will replace them and report back, hopefully this will take care of the problem
  12. thanks for the suggestion man... my injectors are all plugged in, i'll look into wires if putting in Motorcraft plugs doesnt help.
  13. I too agree wth the sparkplugs as being an issue but also you said you put wire on @15k ago, who's wires? alot of these aftermarket 39.95 wire sets are pure junk. if the plugs don't solve your issues, get a set of OEM Ford wires. you would not believe how many cars we get in our shop that have the same issues and had aftermarket set of wires sinstalled, our techs put on the factory Motorcraft wire set and "boom" problem solved.
  14. Randy, the wires are genuine 8MM Motorcraft. When I bought the car (@65k miles), the guy I bought it from had the plugs and wires changed at the dealership, and I have the receipts from that work in my folder of car stuff. The car now has about 81K on it. If the plugs don't solve the problem, would you recommend a set of 9MM Ford Racing wires? I like them because I can get them in red to match the car and they aren't too expensive.

    For that matter, what are the odds that it is a coil pack crapping out?
  15. well maybe you've hit on something here, I have been selling alot of coil paks for the 96 to 98's latley, Ford ones arn't cheap at @$79.00 each

    the Frpp wires are ok to use but if your Ford wires are fairly fresh, I would wait on replacing them just for the "bling-bling"

    get the miss straighten out first.
  16. keep us posted on this.
  17. I'll definitely keep you guys updated. I'm going this afternoon to pick up stock replacement Motorcraft Platinum plugs. Randy or Mike, any idea what the stock replacement plug part # is for a 1997 GT? I don't want to end up with the wrong ones. If I go to the dealer they should know though, right?
  18. AGSF-32PM is the stock plug.

  19. not really, I would drop 1 heat range and do not do platinums. get a set of Motorcraft AGSF-22C-F6 gap them at .050

    now the new plugs will be of the "full thread" design which replaces the old "1/2 thread" design plug, not to worrie it will work just fine.

    if your dealer can't get you the plugs, let me know as we have plenty at $1.95 each