I have a 2007 V6 Mustang with about 10,000 miles on it.
Recently, a very weird issue has been happening with the transmission when in overdrive.
When warmed up and once in overdrive (40-45 mph) if you continue to accelerate while staying in overdrive up to 50-55 mph, the car will sort of lurch/sputter. When this happens, the RPMs don't move, no lights come on, etc.
The first time it happened, the best way I can describe it is that it felt like it was running out of gas.
It will only do this in overdrive. If you turn the overdrive off, it accelerates in top gear as smooth as can be. With the overdrive on, if you step on the gas hard enough for it to pop out of overdrive, it will also accelerate as smoothly as can be.
I took it to a dealer this week and they had it for 6 hours and ran every test in the book (so they say) and everything came back normal.
Nonetheless, it still does this is very annoying. Any ideas what could cause this? It's been happening for a week or so now and does it every time I drive. Thanks for any help.
I think I had the same problem a few weeks ago on my 2005 V6 Automatic. The problem happened many times, but only for a day. Its like it didn't want to go down from high gear when slowing down and putting on the gas. I don't know if this fixed it, but I popped the hood and re-sat all the spark plug connectors and put fresh gas in. I'd be interested to see if you can figure it what it is as I've this feeling it may happen to me again.
It's interesting you mention about the spark plugs because I recently had them changed. I had the stock Motorcraft plugs taken out and put in AutoLite XP 104 which is supposed to fit in the V6 Mustang. I didn't think this could be a problem because if something was wrong with the spark plugs wouldn't you notice an issue with the engine/transmission pretty much all the time? But I do find it odd that it started right after I changed the plugs. And I've put gas in it recently so that's probably not it.
Hmm. Spark plugs? Thinking about it I had a 30K service a couple of weeks before the car 'problem' day, and they probably changed my spark plugs too (as well as a bunch of other stuff). Wonder if changing them would fix your issue? Might not be related, as you're right - you think you'd see it all the time, just throwing it out there.
On that note, I bet the shop put in the cheapest ones they could find in mine. Wonder if there are any better spark plugs out there to get more performance?
Well i am going to try re-sitting now and see if that does anything. But there are several kinds of performance spark plugs out there, whether they do much or not who knows? I got the AutoLite but i have heard very good things about certain kinds of Bosch.
The problem stopped for a few days after I messed with the spark plug wires. But now it is back again and even worse it seems. The hesitation is stronger and it also hesitates when under hard acceleration. I'm thinking now it may be a fuel filter / fuel pump issue. Still no check engine light though.
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Weird Overdrive Problem - 
