Is My Gt Normal?

Discussion in '1996 - 2004 SN95 Mustang -General/Talk-' started by jefx, Apr 30, 2014.

  1. Hi. Im new here. I just bought a 2002 GT with 91,xxx miles
    Build Date: 10.06.2002
    Vehicle Line: Mustang
    Body Style: Coupe
    Version: GT
    Engine: 4.6 SOHC EFI
    Transmission: 4R70W (AODE) 4-Speed Auto Trans
    Drive: LHD RWD
    Axle Ratio: 3.27

    I changed plugs (autolite plats), fuel filter, air filter, cleaned MAF, cleaned IAC, replaced EGR, fixed vacuum leak, changed oil and trans oil, and unplugged battery to reset ECU.

    It has no CEL or pending codes according to my Actron scanner.

    pre-tune up it ran 7.9 sec 0-60 with trac off
    post-tune up it runs 7.6 sec 0-60 with trac off
    my 2012 base 3.7 auto with 2.73s runs 6.9 sec 0-60 on the same stretch.

    it feels really rough, loud, and restricted, but still has enough torque to squeal tires at launch and sometimes chirps shifting into second.

    The idle is inconsistant and occasionally stumbles to an almost stall, especially when heat or a/c is on. It also sometimes lurches during acceleration and temporarily feels smoother and faster (feels great!), but always returns to the grumpy restricted feeling right afterward.

    it also doesnt want to start sometimes... especially after i have been driving it hard. it will crank over fine, but just doesnt fire up. it always starts fine from a cold start.

    The alternator seems fine... its runs normaly after I disconnect battery, even with lights and radio on.

    it sounds and feels "grindy". no pinging, but sounds like it labors to pick up rpms, it feels "heavy". I was expecting it to rev up faster and decel faster then it does....

    My wife and I raced my 2 stangs. She in the 3.7 and me in the GT. The results were just as the times I posted. the 3.7 was a couple car lengths ahead when she let off around 75 mph.

    Heres some Actron readings at warm idle:
    ABSLT TPS% 19.2 (92.6 at WOT)
    CALC LOAD% 26.2
    MAF FLOW GR/SE 5.31
    IAT F 51

    Is this car normal? I have zero experience with this car/engine and I dont know what to expect. I realize its not a race car in stock trim, but Ive read that the factory spec is supposed to be sub 6 sec 0-60, and this car is far from that mark. I just want it to run to its engineered potential, and I dont think it is. Any advise/help is appreciated. TIA Jeff
  2. Maybe check those ignition coils. And check the alternator volts with a voltmeter. I think its supposed to be in the 13s while the engine is running.

    As far as performance, the auto equipped New Edge GTs are not strong performers bone stock. Even back when they first came out they were pretty lame compared to whats out there. Autos are around a mid 14 to a low 14 (low 14 on a very good day). Manuals are around a low 14 to maybe a high 13 (high like a 13.9 on a good day). A stock 11-14 V6 Mustang can easily match and beat an auto New Edge. So don't feel bad.
  3. IDLE RESET PROCEDURE - copied from another forum....

    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 accurate 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!!!


    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 proceed 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 within 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.
  4. Thanks for the replies. I also have a 2004 F150 and I have experienced bad cops before. This GT isn't having the same bucking missfires as my truck does with a bad cop, and the misfire test comes back clean on my Actron. I am going to clean them up anyway based on the advise.

    I will try the idle reset, but Ive read a bunch of conflicting info about setting the TPS. If the signs are pointing to a bad TPS, I would rather just replace it.
  5. Sorry, I'm not much help with the 4.6, but you're right about the TPS