kjs474

When I get to 40 mph, the revolutions on the engine immediately drop to about 1,200 and stick. If I press the accelerator, it gains speed very slowly and the rpm's go up extremely slowly as well. Does anyone know what this could be caused by? Thank you.

Young_Gun

Shifting into the overdrive gear lulz

In my 07 v6 thats about where I was at 40. Not quite 5th gear but a bit too much for 4th.

In my 06 GT 5 speed, I go to 5th at about 40

kjs474

It's an automatic though. My apologies, I don't know much about the gears in cars, but I'm assuming you're talking about a stick-shift?

kevinmalec

Maybe automatic transmission slipping?
I have a 5 speed manual and have never experienced that.

Young_Gun

Doesn't matter lol, you still have gears

But, I haven't driven a v6 Mustang in 6 months, so listen to them over me haha

aaquib1992

+1. I have an auto, and although tuned- even when stock if I hammered it I would occasionally get a downshift if the car felt it was in the wrong gear. You could have a variety of problems, or none at all and just be suffering from throttle lag.

You say you're having weird rpm issues, try cleaning the throttle body as this is commonly the source of wandering idle issues.

You said the car goes up in rpm very slowly? Can you elaborate a little more, like is it a hesitation or just VERY slow acceleration? Could very well just be bad gas, how many miles since you swapped out the fuel filter? Do you have an aftermarket tune?

Derf00

A stock auto mustang is very, how shall we put it PC...sluggish. It's tuned for MPG not performance.

1200 rpm at 40 mph is 5th gear (Over drive on). Try turning the OD off (button on the side of your pinky). YOu'll know its off because there will be a light that pops up on your dash telling you its off.

Anyways, in 5th these cars are dogs so if you only moderatly press the pedal it will stay in 5th and just accellerate...very slowly. With OD off , the highest gear the tranny will use is 4th unless you redline it in 4th, then it will shift to 5th.

If you leave OD On (no light on dash) Next time the car is cruising along at 40mph and the RPM are around 1200. Floor it, it will down shift a lot faster. Practice without traffic though so you don't end up rear ending someone...

On a site note, a good aftermarket tune can adjust that sluggishness out and make the tranny wake up. I did that in mine and even on Moderate throttle it is way more responsive.

Nuke

Will the tranny downshift at that 40 MPH, low RPM, if you get on it or only if you go WOT? Is this something that just recently started or has it been doing it for a long time?

As stated above, the 4.0L V6 is kind of a dog (my wife has one... the 4.0, I mean...) but it should respond to mild acceleration at about 40 MPH in 5th gear by downshifting to a lower gear. There could be many reasons it's not; many of which are easy, inexpensive fixes. But we need more info.

Young_Gun

I'll go out and see how many RPM's I'm at in 5th gear at 40. It should be similar, as I'm not tuned yet.

Nuke

I'd certainly disable OD (5th gear) and confirm that she'll at least spin-up to higher speeds and RPM's, just to narrow it down to the tranny not downshifting properly. Of course, if you're babying it in 5th gear and not giving it enough throttle to downshift then it WILL just seem to sit there and not pick up much speed...

I'm guessing about 1200-1300 RPM at 40 MPH in OD with 3.31 gears. I'd check my speed vs RPM spreadhseet but my excel is hosed up and I can't get in it.... yet.