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Discussion Starter #1
I am having a problem with my 2006 Vulcan with 168k miles on it, chugging or bucking a single time at around 40-45 mph. AC off. Usually at a slow acceleration up a slight hill at part throttle. I can also get it to double or triple chug or buck on a level when I try to keep the speed at 42- 45 mph. I am thinking it is a transmission related issue since it is only at that speed range.

I replaced the ignition wires, plugs, air filter and cam synchro last spring with Motorcraft parts. Plugs I will have to check brand but all were checked for gap. I pulled the upper manifold and cleaned it and regasketed everything, even the manifold runner valve. Idle is perfectly steady at approx. 600 rpm. Transmission was had fluid and filter changes every 40k or so, with the last change before the winter.

The only issue that doesn't seem 100% right is the injectors are making more noise than any of my other two Taurus. Not sure if that is anything to be concerned about. Almost sounds like a bad cam sychro but I have listened to that with a mechanic's stethoscope.

I have gone through the search function and found two related problems members had. One member ended up selling the car before he found the problem and another seemed to think it was a collapsed air filter.

I have run the codes and there are none. I noticed that ForScan has a couple of torque convertor parameters that I can check while I am driving to verify its function. I think I saw torque convertor pressure and solenoid.

I am open to suggestions on possible causes. I really don't know very much about the transmission on these cars since the ones I have had usually last over 240k miles.
 

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It does sound like lockup converter chuggle. If you've been doing pan drops, then only about 2/5 of the fluid gets changed each time. A full 12-16 qt Mercon V flush using a shop flush machine is more effective at transferring all the old fluid that gets trapped in the converter.
 

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Discussion Starter #5
I drove around in drive instead of overdrive and I didn't feel the buck but I still need to drive it like that for another day or so to be positive.

On the fluid and filter change issue above, the normal process for me is to suck out the 8 quarts and the add new fluid back in. I drive for a 100 miles and then do a pan drop and fluid change. This last time I didn't do the initial suck out of fluid but did the pan drop and fluid.

I am thinking it may have something to do with overdrive and not the torque converter. I may try the red tube additive that contains friction modifiers.
 

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I have been monitoring torque converter lockup on my 03 with a small GPS sized scan tool for many weeks now. It is absolutely amazing how frequently the PCM is at least partially unlocking the convertor for no apparent reason. With the original PCM code you could feel some of these actions as the converter re-lock was much quicker. With an update version of the PCM code it is quite hard to feel as the re-lock is very gradual. Lock and unlock at very light throttle are quite close together in throttle counts.
 

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Discussion Starter #7 (Edited)
Well I have been driving the 2006 Taurus and trying to find out exactly the reason for this random buck at 40-45 mph. It seemed to do it even when in Drive instead of Overdrive.

While driving my car today I had to go up a hill I normally don't go up. It is a very steep hill and I lost a lot of power and I shifted down to Drive. The car set a code. I then drove another 80 plus miles and felt a bucking more frequently than usual. I read the code once I got home, P-0352

Code: P0352 - Ignition Coil B primary circuit malfunction
Module: Powertrain Control Module
Diagnostic Trouble Code details
Ignition Coil B primary circuit malfunction
This DTC may be caused by :
Open ignition coil primary circuit.
Short to ground in ignition coil primary circuit.
Open ignition coil POWER circuit.


I ohmed the primary coils and got around 7.4 ohms on all. I then ohmed the connector from red lead to each coil signal and got around 1100 ohms on all three leads. Not sure if it is valid but I thought it would at least indicate a bad wire or a bad driver circuit.

I pulled the coil and notice the coil is all cracked. This is actually a coil off my 2001 that I swapped two years ago when I was getting a very rare one time buck. I will replace the coil because of the cracks but not sure it's the issue. I wasn't getting a misfire code.

Well I guess I will do another swap with one of my 2001s to test a new coil also.
 

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I have been monitoring torque converter lockup on my 03 with a small GPS sized scan tool for many weeks now. It is absolutely amazing how frequently the PCM is at least partially unlocking the convertor for no apparent reason. With the original PCM code you could feel some of these actions as the converter re-lock was much quicker. With an update version of the PCM code it is quite hard to feel as the re-lock is very gradual. Lock and unlock at very light throttle are quite close together in throttle counts.
I read in an older thread that the programming is terrible and the A/C clutch engaging actually causes the torque converter to unlock and re lock for a split second. It's very blatant when you're cruising in lockup at about 45MPH.

Well I have been driving the 2006 Taurus and trying to find out exactly the reason for this random buck at 40-45 mph. It seemed to do it even when in Drive instead of Overdrive.

While driving my car today I had to go up a hill I normally don't go up. It is a very steep hill and I lost a lot of power and I shifted down to Drive. The car set a code. I then drove another 80 plus miles and felt a bucking more frequently than usual. I read the code once I got home, P-0352

Code: P0352 - Ignition Coil B primary circuit malfunction
Module: Powertrain Control Module
Diagnostic Trouble Code details
Ignition Coil B primary circuit malfunction
This DTC may be caused by :
Open ignition coil primary circuit.
Short to ground in ignition coil primary circuit.
Open ignition coil POWER circuit.


I ohmed the primary coils and got around 7.4 ohms on all. I then ohmed the connector from red lead to each coil signal and got around 1100 ohms on all three leads. Not sure if it is valid but I thought it would at least indicate a bad wire or a bad driver circuit.

I pulled the coil and notice the coil is all cracked. This is actually a coil off my 2001 that I swapped two years ago when I was getting a very rare one time buck. I will replace the coil because of the cracks but not sure it's the issue. I wasn't getting a misfire code.
Very strange...
 

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Discussion Starter #9
I replaced the coil pack today with a Motorcraft one. Old coil ohmed out the same as the new one on all primary coils. I reset the codes and took it for a 10 mile drive and it did not chug or buck. I will not claim fixed until I drive it for at least a week but it's promising.
 

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Coils heat up and expand internally and get intermittent and can / will finally fail. Good catch, I see coils do that in my line of work all the time. Common problem on gas valve coils in dryers.
 

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Discussion Starter #11
Well to help people with similar problems in the future the replacement of the coil has fix the problem it the chug. Thought it was a failing trans or solenoid but luckily it was not. Shifts really smooth. Must need a good spark to help shifts.
 

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Glad that was an easy fix. Took a full year for me to find that one on mine with the airfilter.
 

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Discussion Starter #13
Thanks I was glad it was only a $85 Motorcraft coil. I am checking my MPG because when the coil was bad I drove 80 miles at 45-55 mph on country roads and got 27.8 MPG. Seems good for a bad spark.
 

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I bet it only misfires under the right conditions, low RPM higher load.
 

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You know.... you have me thinking about my 03 now. I have a slight chug at idle(been that way since I fixed the PCV issue, correcting the idle). I replaced the plugs and wires and had the same issue. It doesn't happen all the time. The coil 'looked' new like it was replaced before I bought the car but I never inspected it. I have to look at that today now to see if I find any cracks or if it was an el cheapo replacement.
 
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