2nd Gear Downshift Missing/Backfire

FL2005GT said:

If I do a high-RPM downshift to 2nd (putting RPM's at 4K+) to get on it for fun/passing, I sometimes get serious stuttering and even a small backfire if I do it too quickly. If I blip the throttle to match revs (not easy with the new ETC system) or slip the clutch a little bit, this stops it from happening entirely. Only an issue downshifting to 2nd, never 3rd or 4th.

This may be normal (in other words, my bad driving by popping the clutch too quickly), but it's just something I never experienced driving my 2000 GT or the '89 GT I used to play with sometimes. On those, I could be going 40 or so, do an abusive downshift to 2nd, chirp the tires and go with no hesitation or...I don't know...maybe it's drivetrain lash. I've never had it happen on any of the other sticks I've driven, either.

Only mod I have is axle-back Flows.

Anyone else run into this?

Click to expand...

Get a tuner,its probably the torque managment or TCS. I hated it before I got a tune. Does it do it with the traction control off?

yeah, if you really get on it with the TCS on nono: ), it will fall on its face. its in the computer. ford wants to give you 300 horses, but it wants its parts to last for a while as well.

Problem

You aren't hitting the rev limiter are you?

dont know if this is right... but...

doesnt it studder because of the syncros in your transmission have to do the rev match because you didnt do it with the throttle?

or maybe is the clutch that rev matches... but i always thought it was the syncros... thats why people with busted syncros have to rev match... but it could also be the clutch... well... if it is the syncros replace ever instance of the word clucth in the next couple paragraphs with the word syncro... lmao

your clucth has to grab the crank and make the engine spin as fast as the driveshaft is moving...(i understand that the driveshaft and clucth go different speeds depending on what gear ratio and gear the trans is in... this is just oversimplifying it)

Example:
since youre in 3rd going ~2000rpms and you downshift to 2nd the driveshaft is still going the same speed but in order for the gear speed to match up in the trans. the engine has to move up 2000rpms quicker putting it at ~4000rpms... but since you didnt rev match the car jerks when you let the clucth out quickly because it is grabbing the engine and turning it faster... this would explain the smooth downshift when you rev match or slip the clutch (slipping the clucth works because you are giving the clutch a chance to slowly turn the engine faster... instead of dumping it and making it happen suddenly)

ANYWAYS... this is pretty normal... well that is if your talking about what i think your talking about...

my car does the same thing and its a 99 v6 5-speed


edit: about it not happening in 3rd and so on... going with my theory.... the driveshaft has alot of momentum (because of the higher speeds) so it (the clucth) is able to turn the engine fast easier hence it being smoother... in other words no studder

Sounds like when your downshifting you might actually draging the back tires for a second. If the TC is on....it might think your sliding and start pulling timing, fuel, etc.

Mine will do it as such: I will be on the interstate, 75mph, then get on a ramp to merge onto another interstate. I put it in 2nd for the ramp since it is a slow curve. I match my revs, and let the clutch out slow, and am proceeding along in second gear, ~3000rpm down the ramp. When I reach the interstate again I gas it good in second to merge, and it will hesitate and stop so bad that I go forward in my seat from the decelleration. Not my idea of a safe way to merge, but I guess I don't ever really need to accelerate quickly in low gear in a sports car. Also, this almost only happens when dropping down gears from highway speed and then resuming highway speed quickly in that gear again. Who knows.