still can't get rid of misfire!

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


  1. Brute03

    Brute03 Member

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    a shot alternator can indeed cause some strange problems. my car was misfiring pretty badly and it threw a camshaft sensor code and mutiple misfire code, after two new sensors it still wasn't fixed.

    turns out it was a bad regulator, but instead of getting a new alternator i got it rebuilt. now it's bucking and jerking again in any gear under 2K rpm and the car is a real dog, i've only been getting 11-12mpg!! so i'm gonna get a new alt. and hope for the best
     
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  2. stangGT97

    stangGT97 New Member

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    alright man thanks for the input! keep me updated on your situation, and I will do the same
     
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  3. stangGT97

    stangGT97 New Member

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    just picked up a PA Performance 130amp alternator (stock replacement) for $190 off of ebay, free shipping. we'll see if that helps
     
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  4. Brute03

    Brute03 Member

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    alright man, lemme as soon as you get it
     
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  5. stangGT97

    stangGT97 New Member

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    ok, I never received the alternator due to paypal complications. Here's the scoop with what's been done thus far:
    New Accel coilpacks,
    New 8mm motorcraft wires
    New AGSF32PP plugs (I believe that was the code, theyre right anyway)
    New PCV
    New DPFE sensor (thought the EGR was opening erratically)
    New airfilter (motorcraft)
    Cleaned MAF, replaced IAC
    Alternator could probably be replaced but no charging issues really
    New clutch
    4 New O2 sensors

    Yesterday I started the car (it sat for a day) and it misfired like crazy - the whole car was shaking, could be heard from the exhaust (almost like a cylinder wasnt firing at all), but gradually smoothed out after a minute or so. The motor itself was shaking in the engine bay. If I'm cruising along at 2100 in 4th, then pop it into 5th gear - keeping the throttle light, I feel the car jerking pretty distinctly, RPMs are generally at right around 1400-1500. No codes are being thrown.

    I have noticed what I think is an exhaust leak, I hear it when I'm driving next to another car or by a building (a tap sound), not to mention I can smell some exhaust when stationary. I couldn't tell you where the leak is coming from, I had my clutch done but I crawled underneath and made sure everything was torqued properly.

    svttech76 recommended a leakdown test but I have no idea where to get one out here in Ohio. What do I do? Can an exhaust leak cause part throttle bucking?
     
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  6. Brute03

    Brute03 Member

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    yes a leak can cause some issues due to the corresponding o2 sensor getting an inaccurate reading
     
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  7. stangGT97

    stangGT97 New Member

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    I guess I'll have to take it to an exhaust shop to have it checked out. I guess that makes sense why it would misfire after sitting for a while, the seals probably shrank up and make the leak larger
     
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  8. Mike97gt

    Mike97gt it doe snot Mod Dude Founding Member

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    I would fix the exhaust leak and see if that helps. after that I think I would start to suspect the PCM in your car.
     
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  9. stangGT97

    stangGT97 New Member

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    okay thanks for the advice... I'll have to find a decent exhaust shop around here and have them locate the leak. Out of curiosity, how does the PCM get screwed up? Electrical surges or heat? And does a faulty PCM cause the problems I have been having? thanks!
     
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  10. tomustang

    tomustang Psychotic Member Founding Member

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    I see them lurk
     
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  11. stangGT97

    stangGT97 New Member

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    can a bad MAF sensor cause this low rpm bucking? I was on the 5.0 forum and a guy said that was the remedy to a misfire problem he was having that sounded similar to mine. I know they're not the same engine but it's just an idea. I did drop the MAF when I was installing my CAI about a year ago but as far as I can tell the sensors are intact. Could they be damaged without me being able to see it?
     
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  12. 40oz

    40oz Member

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    For God's sake, take it to a dealership and have them look it over and diagnose the issue. Don't try to tell them what to look at or what you thinkk is wrong, just describe the symptoms and let them figure it out. You don't have to have them replace the easy stuff, but pay someone who knows what they are doing take a look at it. You can go on and on here with a car that never runs right, chasing phantoms and spending money and never fix the problem, or you can turn to a professional, get it fixed in a day, and not have problems anymore. You make the call.
     
    #72
  13. stangGT97

    stangGT97 New Member

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    o wow calm down there buddy. The main reason I dont take it somewhere is because it's my main mode of transportation, and since it runs, I can still take it to work. I'll take it to a dealership but I don't know how I'm going to get around since I don't know anyone out here. Have some patience, no one's twisting your arm to read this thread. Someone down the line who is having the same problem can search and find some of the things that could be causing their own misfire and might have better success in solving the problem. Most people never follow up with their problem threads and maybe I understand why, if they just get attitude from people for wasting their time.
     
    #73
  14. squares98

    squares98 Member

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    40oz. does have a point, dont be so quick to bite.
    If your PCM or some harness is bad you will never know until you drop off your car at Ford. Plus a rental car is only about $25 a day.
     
    #74
  15. COramprat

    COramprat Drone Driver Mod Dude

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    Exactly what the dealer wants...pay twice as much for them to do the same things he has already done. We have a tech section on Stangnet just for this purpose. To help find a problem and maybe save someone some cash in the process. Lord knows I've saved a ton asking questions here.

    Now...back to our story...
     
    #75
  16. dz7b7h

    dz7b7h New Member

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    Have you put a scanner on there to make sure you aren't getting any codes. I have a 97 GT Vert and she's been known to throw codes without triggering the CEL. I had the exact problem you are having along with a short in the PCM wiring. You want to talk about a PITA!!! Don't give up man. I got mine straightened out and I know very little about cars.

    Also, noticed that you have a PI Intake... Did you use adaptor plates or rtv? Could be blown RTV... have you made sure your TPS is reading right? If you are getting spark, which I think with everything that you've done you should be
     
    #76
  17. stangGT97

    stangGT97 New Member

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    thanks for the tip... I never thought to get it scanned because I have no CEL. I used the RTV method but I don't think its a vacuum leak bc I have a stable 800rpm idle, it's just that there are little exhaust blips at idle and this 1500rpm misfire. I will take this down to Autozone and have them check for any codes and I'll see if I can get them to vacuum test the manifold to see if that may be an issue. I did check vacuum right after the install (1 yr ago) and it was right up to par, but things change over time anyway.

    Thanks a lot for your suggestions! If I don't show any codes or any vacuum problems, then I'll hand it over to the dealer before I'm tempted to push this off a cliff
     
    #77
  18. dz7b7h

    dz7b7h New Member

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    Ever since I upgraded my CAI, tb and plenum anytime I disconnect the battery I have to go through the entire process of disconnecting the IAC and letting the car restablish idle.. if i don't it misfires and acceleration sucks..
     
    #78
  19. stangGT97

    stangGT97 New Member

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    What does this process entail? Maybe I'll give it a shot
     
    #79
  20. dz7b7h

    dz7b7h New Member

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    DO NOT TOUCH THE GAS PEDAL!!

    What you will need: a mutlimeter, a big screw phillips screwdriver and some sort of small metal piercing tool
    What will be handy but not necessary: an extra set of hands, a scan tool that will give you live data readings. you can rent one from O'Reillys or Autzone.

    You will probably get a million different responses on how to do this. This is how I have done it and it works for me. And I've done it a lot. Refer to short in PCM wiring :lol: :bang:

    1. Disconnect the negative terminal to your battery and turn on your headlights for about 10 minutes(there's a lot of speculation as to how long. some people will even say to disconnect the positive terminal and some people will say to leave it disconnected over night.)
    2. Disconnect the wiring harness connector to the IAC
    3. Turn off headlights and reconnect battery. DO NOT TOUCH THE GAS PEDAL!!
    4. (People will probably argue over this step) DO NOT TOUCH THE GAS PEDAL!! Try to start the car. If the car won't start adjust the set screw on the throttle body a 1/4 - 1/2 turn and try again. Repeat until the car will stay running. It will run rough but that is what you want. (some people will say to turn the set screw a few turns before starting your car then turn it down until the car idles at 700rpm or so then)
    5. Either way you go let the car sit and idle (DO NOT TOUCH THE GAS PEDAL!!!) until the car reaches operating temperature which to me is when the needle moves to the right leg of the letter 'N'
    6. DO NOT TOUCH THE GAS PEDAL!!! Step 5 allows the computer to relearn idle settings. It's pretty cool when you follow my procedure because you can actually hear and feel the car figuring out the proper idle settings. It will go from idling rough to idling smooth as it warms up. Once the car is warmed up verify that the car is idling at around 700rpm. (this is where the scan tool comes in handy cause you can be more accurat but eye-balling it works too) If the car is not adjust the screw until it hits ~700rpm and then let is sit maybe another 10 minutes DO NOT TOUCH THE GAS PEDAL!!!

    DO NOT TOUCH THE GAS PEDAL!!!

    Turn the car off. Reattach IAC wiring harness. Now some people out there will tell you that this step is not necessary but I totally disagree. Remember we adjusted the set screw on the throttle body. That means that the voltage reading from the TPS sensor has changed. It should read between .96 and .99 volts. (someone correct me if I am wrong) Anything outside of that range will cause all sorts of issues including misfires and rough idle.

    7. Now this part you may want to look up and verify before you go piercing wires. What I do is I stick the middle wire with a metal pin, a heavy sewing needle works pretty good (I think, it may be the top wire if you are viewing the connector while still connected) some people just peel off a piece of plastic wire cover because they have to do this so often.

    8. Set your multimeter to volts. Turn your car to key, on engine off. then place your positive lead of your mutlimeter on the metal pin and your negative to some ground point. If it comes up as a negative that is okay as long as you are -.96 to -.99. If you get this reading then great you are done and hopefully your issues are gone. If not procede to step 9

    9. This is where and extra pair of hands come in handy. Using a large screw driver you will need to loosen the bolts that hold the TPS. DO NOT USE A SCREWDRIVER THAT IS TOO SMALL BECAUSE YOU WILL STRIP THE BOLTS. They probably will be really tight so you have to really lean on the screwdriver and use some finesse. They will come off. Just don't try to turn the bolt all at once or you will strip it. A lot people have broken their TPS from being too rough with these bolts. Again, I'm not a mechanic by any means but just use some common sense.

    10. Once the bolts are loose you will need to move the TPS up or down and continue to read the voltage. Once you get it to the desired setting you can retighten the bolts. What I do is I find .97 and then as carefully as possible I tighten the TPS down. what will happen is the voltage will change usually to
    .96 or .98 but that it okay. Once you are done with this manually open the throttle body a few times and close it then reread the voltage and make sure it is still withing our desired range.

    11. You should be good. I would put a little putty on the whole you made with the pin. Drink a dozen beers or so and crank you car. DO NOT TOUCH THE GAS PEDAL!! I would give the car a once over, make sure nothing came loose while you were messing around under the hood. Let the car idle for a few minutes then take her for a spin. You may want to wait on the dozen beers.

    I hope this helps and fixes your problem. Like I said I had a similar issue and it turned out to be a cobination of a bad set of MSD wires only a few months old and a bad TPS. Shortly after that my EGR valve S%^T the bed and then my car developed a short in the lead wire for the PCM effectively resetting the computer every time it blew a fuse. But, I hopefully have it all fixed now. My car has been running smooth with the exception of a slight misfire due to some corrosion on one of the spark plug wires. I cleaned the connectors and have been golden since.
     
    #80

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