Eljay S

My wife's 2006 Mustang V6 automatic (130k mi) last week started up-shifting hard from 2nd to 3rd. (Down shift is okay.) And sometimes even 1st to 2nd can be hard. It's like a jerk that can throw your head back and a slight bang is heard.

But I noticed that if I drive it a certain way, it is shifts smooth as silk. When I continue to depress the accelerator further through those gears, it is fine. It's hard to explain – I keep downward motion on the accelerator instead of just 'riding' the gas pedal or keeping it stationary. (Sorry but it's hard to describe.) If I ride the gas pedal or depress it slowly, or let up on it as those gears change... WHAM... I get a really hard shift. Being those gear changes happen at about 10 and 20 mph, it's not hard to use this technique to overcome the issue, but there is an issue, obviously.

A few weeks before this started, I diagnosed the front passenger side cat converter rumbling and am about to have it replaced. I had the spark plugs and wires changed the day before it started the hard shift. (I had the plugs and wires double checked for proper installation and gapping.)

I'm not a mechanic and not wealthy enough to pay a shop for everything on our car, plus I like to learn about it and get away from my job in computers. So, in researching this, I heard the bad cat converter can overheat and cause the tranny issues, but more probable, it seems to point at the TPS, being I can overcome the issue by working the gas pedal differently. And I ruled out a bad spark plug job, as in misfiring.

So, that's my information and my guess. I'd like to know what you who are more familiar with these things think. And if it is the TPS, can you help me with info on diagnosing it and replacing it?

Thanks!!

Eljay S

Update: Replaced catalytic converter and now transmission shifts smoothly again.

66and06stangs

Wow, how does a catalytic converter have anything to do with the way a car shifts?

jwog666

a restricted converter will reduce engine power, this in turn causes the driver to push harder on the accelerator to get the desired acceleration, this increases engine load, and due to this the pcm ramps up transmission line pressure in anticipation of a high load upshift = harsh upshift

Eljay S

Yes, actually, two of the best exhaust shops informed me ahead of time the bad cat converter might be the tranny problem. So, it must be a fairly well known thing in their area of expertise.

jwog666

yes i have personally seen it several times. to the inexperienced, it sure does seem like a trans concern. i fell victim to this 1 time very early in my career lol. so i am always on the look for it when confronted with a "customer states transmission problem" concern.

Derf00

Learn something new everyday...

movielover40

Never would have guessed that.