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V6 S197 General Discussion This section is for technical discussions pertaining specifically to the V6 variation of the 2005 and newer Ford Mustang.

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Old 07-12-2013, 11:42 PM   #1
Magnum's Mustache
 
Join Date: Jul 2013
Vehicle: 2007 Mustang v6 4.0
Location: Texas
Posts: 2
Default 2007 v6 tensioner shake and missing at high rpms

Hello forum! I have a technical question concerning a recurring problem I have been having. First I will detail my setup and then chronologically go through what I am seeing.

I have a 2007 V6 4.0L Mustang that has 155k miles on it right now. It has the standard setup, no mods or anything fun like that. Iíve taken good care of her, regular oil changes switching to high mileage around 100k, filter changes, fuel filter, motorcraft spark plugs, basically all the right stuff at the right time. Itís been good to me. Texas housed, very warm most of the time.

About a year ago, I noticed that she started rough every time. She would start up, regular rpms, then drop and sound like she was going to die, then recover a few seconds later. The stang would shimmy just a bit in the process, I could feel it in the pedal. Afterward, no problems. I thought it was a fuel problem. I ran some Seafoam through it, cleaned the MAF and throttle body, new belt, and changed the plugs out again with Ford parts. Seems to be a bit better (could have been in my head) but was still there, so I kinda gave up and it seemed to slowly recover. I wrote it off to possibly be some bad gasoline or maybe e85 got in there. Not sure, but the problem seemed to resolve itself on its own. I was still a little concerned about it.

So now about a few weeks ago I realized it seemed like my alternator was grinding louder. I noticed some other signs of alternator failure. So I checked voltage. Battery was good, 12.6 or so with the car off. Running, about 13.5 or so. Turn on AC, lights, and defroster and it dropped like a rock back to 12.7 or so. So it seems it could not keep up under load. I had it tested at Autozone to make sure and the machine said it failed. So I bought a new one. I also noticed when I was under the hood before that the tensioner was jumpy, seemed to be bouncing around a lot more than it should. Seeing as it was never replaced, I went ahead and replaced both parts (alternator was remanufactured). So, alternator is now kicking out the voltage, even under load. Thatís good.

Now the tensioner is still jumpy. Seems to be the same amount of movement as before. While the belt was off, I turned all the pulleys and they seemed fine, no give and no movement laterally. Spin was good. I canít see where the vibration is coming from.

And to top it off, the old rough start is now back. Same symptoms as last year. Really odd. Did the computer reset from having battery disconnected for a day throw the system for a loop? So I warmed it up and revved it to about 3500-4000 and she misses, about once a second, at about 3500. Drops about 500rpm with each miss. No matter the pressure on the pedal she wonít get past this 3500-4000 point. She drives fine under regular conditions, even at highway speed.

So my question is, where should I start with the wobbly tensioner and rough start / missing? Plug wires and coil?

Sorry for the super long story but I felt all the details were relevant. I appreciate the help from the forum, Iíve read for years but never had to post before.
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Old 07-13-2013, 01:41 AM   #2
akdoggie
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Check you crankshaft balancer to see if it hasn't started coming apart. It has most likely decided to give up the ghost. I've never personally experienced this, but was reading that you hit a certain RPM area it will miss due to imbalance. I don't know if that is true, but it would cause a vibration shake. Maybe that is what you are feeling, and not so much a miss?
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Old 07-13-2013, 02:08 AM   #3
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Quote:
Originally Posted by akdoggie View Post
Check you crankshaft balancer to see if it hasn't started coming apart. It has most likely decided to give up the ghost. I've never personally experienced this, but was reading that you hit a certain RPM area it will miss due to imbalance. I don't know if that is true, but it would cause a vibration shake. Maybe that is what you are feeling, and not so much a miss?
I'll check that. Help me with what too look for, however. That was the only pulley I really could not check because of no free spin. I do get a slight visual that it appears the least bit wobbly when at high RPM. I mean it is VERY slight to the naked eye. I will inspect closely, am I looking for cracks, movement, etc?

Replacing one of these seems complex but within my limited expertise, I just don't want to do a needless repair. Thanks for the reply, however!
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Old 07-13-2013, 06:52 PM   #4
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Try this. Take a piece of chalk and mark a straight horizontal line from front to back on the balancer and pulley. Start your engine and give it a couple thousand rpms, then let off and stop the engine. Check the chalk line and it should be where it was when it was started. If it is off, then you have a bad balancer. The two pieces will turn if it is bad, and they can be 180 out with no problem. That's how I'd do a quick check. Good luck.
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Old 07-13-2013, 06:52 PM
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