Bucking on acceleration

Discussion in 'SN95 V6 Mustang Tech' started by Sparkle, Jan 30, 2010.

  1. Need some ideas please... I'm pulling my hair out!
    Ever since last summer, my 03 mustang 3.8L manual has been running rough and hesitating on acceleration. It's noticeable in 1st bucking at about 1700RPM, bucks if I take off from 2nd gear, in 5th bucks at very low RPMs when pressing gas decently. Runs fine and smooth in high RPMs. Here is the history:
    July 09:
    platinum plugs, wires, fuel injector cleaner, fuel filter, radiator hoses, clutch, flywheel
    no difference
    October 09:
    alternator, camshaft sensor, crankshaft sensor, ignition coil pack
    got worse, threw code for coil pack, put old coil pack back on.
    wouldn't even idle, had to rev it hard to run it at all
    took to ford dealer, told me pcm failed. they replaced pcm. one day after it was running rough again. took back to ford dealer, threw code #3 misfiring. they replaced #3 after market plug with motocraft plug. ran great. week later, running rough again, same as last summer.
    January 10:
    put new motorcraft plugs on, no difference.
    today: replaced entire air filter assembly including mass air sensor. tried another coil pack from different auto part store, ran worse, put old coil pack back on. running same as last year.
    what gives?!?!?!?!?!?!
  2. Where are you getting your coil packs from? I certainly hope not from Autozone. Parts from that place have a mysterious tendency to become defective. Their parts they get are of bad quality. Make sure you get it from any other place besides Autozone. Are you running any codes from the CE light? Even if there is no CE light on , there still can be codes in memory. Don't pay a Ford dealer to run diagnostics on it, just go to Advanced Auto or some other auto parts store and ask to have them scan it for you. They'll do it free of charge. I am having trouble understanding why it is running worse with a new coil pack. the only thing I can think of is that you are getting defective units.

    One last question. I noticed you replaced the camshaft sensor. When you replaced it, did you have it re-calibrated? if not then that may very well be your problem. Did the problems start before or after the camshaft sensor install?
  3. Your help is greatly appreciated!!!

    Ford tested my original coil & said it was fine so I don't know what's up with that. No clue why its worse unless I've gotten 2 faulty from autozone & advance auto parts.

    It started running rough in june 09. Everything got worse back in oct after replacing the coil, camshaft & crankshaft. That's when I took it to ford & they said pcm failed & replaced it. I assume they recalibrated everything then?

    Autozone employees had few ideas... MAP sensor... I see all stangs except 3.8 have one, so I guess the MAF takes its place? He also suggested igition control module. Said they would test it if I can get it out, but I can't seem to locate it.
  4. Oh, another idea from someone was the o2 sensors. I realize its good to replace all this after 110k miles, but I've put so much money into it (esp for pcm) at this point I need to just fix the problem & make sure it doesn't blow the pcm again.
  5. Oh, another idea from someone was the o2 sensors. I realize its good to replace all this after 110k miles, but I've put so much money into it (esp for pcm) at this point I need to just fix the problem & make sure it doesn't blow the pcm again.
  6. Excessive EGR flow can cause a Buck or loss of power. Try disconnecting and plugging the EGR vacuum line. It may through a DTC code related to EGR, but it is OK because it is for testing.

    If the condition improves with the EGR vacuum line plugged, suspect bad DPFE. Note: the EGR valve could still be bad (IE, allowing flow when commanded to be closed). If a high mileage car, consider replacing.

    OBTW. A MAP is a manifold absolute pressure sensor. A MAP is used on older Mustangs and is not needed on Mass Air Flow (MAF) cars.

    OBTW2, bucking/lugging also occurs under high load/low RPM situations. I am confused as for the reason to start in 2nd gear. This creates a high load/low RPM condition also needing a lot of clutch slip. Why?

    Also, try using less throttle under low RPM's. The idea is to not destroy engine vacuum with excessive throttle opening.

    Are you doing the work yourself? Consider investing in an ODB2 scanner. Might have paid for itself already considering all of the other parts allready replaced.
  7. Bad EGR is very possible. But at 110k miles it still seems rather unlikely. These parts last a lot longer than say those on a 5.0. I'm not saying the 5.0 is a bad motor (hell no.. :p ), just that the 3.8's run a bit more efficient and EGR don't get clogged easily. Unless you had a constant rich condition. It's usually exhaust soot that clogs up an EGR diaphragm. I've got over 140k miles on my 96 and the EGR is still operating well. I won't rule that out yet though.

    Another thing, there is no ignition control module. Thats why you can't find it. Instead the ignition is controled by the PCM.

    I'm still leaning towards an uncalibrated Cam sensor. Especially that you said everything started just after replacing that.. the crank sensor and the coil pack. It's a common problem. I've seen it a half dozen times already in earlier threads. It is either uncalibrated or the sensor could be faulty. The dealer charges extra for calibrating those. I've seen them installed by dealer service dept's and still not get calibrated. Try this, unplug the electrical connector that goes to the cam sensor and then try driving it for awhile. Trust me, the engine will run fine without it. Just that there will be a slight hesitation in the throttle response. If the problem resolves itself after unplugging the sensor, then it's a calibration issue or defect.
  8. Ford TSB 02-22-1

    Found an interesting TSB that may apply here. It has to do with an incorrect CAM position sensor being installed for the application. Also mentions that the wrong tool (or no tool) being used to sync the sensor.

    Engine Controls - Engine Surge/Rolling Idle/DTC's Set
    Article No.




    1994-1997 THUNDERBIRD
    1995-2003 TAURUS
    1996-2003 MUSTANG
    1995-1997 AEROSTAR
    1995-2003 RANGER, WINDSTAR
    1996-2000 EXPLORER
    1997-2003 E SERIES, F-150

    1994-1997 COUGAR
    1995-2003 SABLE
    1997-2000 MOUNTAINEER


    Incorrectly installed gear driven camshaft position (CMP) sensor synchronizer assemblies may be hard to diagnose. Vehicle may exhibit poor fuel economy, driveability Diagnostic Trouble Codes (DTCs) P1336, P1309, P0340 with MIL light on. Loss of power, surge, hesitation and runs rough on acceleration may also be present.


    New diagnostics have been developed for WDS to diagnose incorrectly installed gear driven camshaft position (CMP) synchronizer assemblies. Refer to the following Service Procedure to diagnose a possible mis-installed synchronizer assembly and proper installation procedure.


    Items Covered In This Article

    ^ "Hall" vs. "VRS" sensor function
    ^ Vehicle history scrutiny for past service of the synchronizer assembly
    ^ WDS - Power balance test
    ^ WDS - CMP and CKP wave signal comparison
    ^ Wave Comparison chart - CMP vs. CKP
    ^ Correct (CMP) synchronizer installation tool application & installation procedure
    ^ "Top Dead Center" (TDC) alignment
    ^ Synchronizer installation tool application chart

    Hall - Effect (Hall) and Variable Reluctance (VRS) CMP Sensors

    CMP sensors are used on all current model year engines, regardless of fuel system or ignition system type. The CMP sensor provides the Powertrain Control Module (PCM) with cam position information to indicate # 1 cylinder, on the compression stroke

    There are two different types of CMP sensors:

    ^ The three-pin, Hall-effect sensor (Figure 1)
    ^ The two-pin Variable Reluctance sensor (Figure 1)

    Although the Hall-effect (three-pin) and the Variable Reluctance (two-pin) CMP sensors perform the same function, their signal appearance is quite different and they are not interchangeable.

    ^ The three-pin Hall-effect sensor uses a Hall effect device and a magnet to generate a digital square wave signal (Figure 2)
    ^ The two-pin Variable Reluctance sensor is a magnetic transducer, which uses differential voltage across windings to generate a voltage waveform that is similar to a sine wave (Figure 2)

    Both sensors provide a switching voltage as the engine rotates.
  9. I'm betting on the EGR problem, since you have good response under high RPM /load conditions. If coil pack or bad plugs /leads etc....... problem would be worse at high load condition.
    Looks to me like the EGR may be stuck slightly open or DPFE problem.
  10. My car is the auto 3.8 and it's been bucking or surging at mid press of the throttle and I've unplugged the egr and it feels better but still does it then I unplugged the fuel rail pressure sensor and it's way better so it might be the sensor or the pump unplug it and drive a bit see if it helps