4.6iS transmission downshifts automatically

[stupenduzzman]

I recently purchased a 2001 4.6iS. I bought it to tow my trailer and racecar around, however I've experienced some interesting things while towing. I always tow in manual mode. First, occasionally when cruising in 5th gear the engine revs will go up by 500 rpm as if it has shifted down but it still says it's in 5th gear and after a little while the RPMs drop again. The RPM change is not large enough for it to be a 4th gear change. What could this be?

Secondly, after cruising for a while and usually while going uphill or with headwind, the transmission will automatically shift into 4th in manual mode. It will not allow me to shift into 5th even if I'm going downhill afterwards. Occasionally it would even shift into 3rd, again without me doing anything. It will get stuck in the lower gear for a short while and after about 5 minutes or less give me control back to shift up.

Background info:
Trailer is an enclosed 18 foot and combined weight of trailer + car is right around 6000 lbs. X5 is bone stock expect for X-pipes in the exhaust and a Prodigy brake controller. I'll use this opportunity to say that the X5 is awesome at towing. I towed 1300 miles recently and apart from the issue above it was perfect. The self level rear end + a weight distribution hitch worked well. It felt super stable, even in ~50 mph cross winds and 65 mph cruising speed. The one and only downside was gas consumption. I barely managed 10 mpg on the first half going 55-60mph and 8.7 on the return trip at 65-70mph.

[RRPhil]

Originally Posted by stupenduzzman

I recently purchased a 2001 4.6iS. I bought it to tow my trailer and racecar around, however I've experienced some interesting things while towing. I always tow in manual mode. First, occasionally when cruising in 5th gear the engine revs will go up by 500 rpm as if it has shifted down but it still says it's in 5th gear and after a little while the RPMs drop again. The RPM change is not large enough for it to be a 4th gear change. What could this be?

This is just your torque converter lock-up clutch engaging & disengaging and is perfectly normal

Secondly, after cruising for a while and usually while going uphill or with headwind, the transmission will automatically shift into 4th in manual mode. It will not allow me to shift into 5th even if I'm going downhill afterwards. Occasionally it would even shift into 3rd, again without me doing anything. It will get stuck in the lower gear for a short while and after about 5 minutes or less give me control back to shift up.

The transmission ECU will override you in manual mode if it feels you are doing something inappropriate. The controller is programmed with a number of driving modes including ‘Hill Mode’ which it automatically engages if it detects a combination of high engine torque, high throttle angle and low engine speed. Different shift maps are used depending upon its calculation of the severity of the gradient which will hold the transmission in low gears to varying degrees.

Phil

[stupenduzzman]

Awesome, thanks!

[epdarks]

Now that we got that out of the way, post some pics of that 4.6is!

[tmv]

[stupenduzzman]

Here's a low-quality picture of the X5 + trailer.



and here's one of the cars that goes into the trailer

[epdarks]

Imola 4.6 = DROOL

I spy an intercooler on your E36. And your fenders look a little wider than stock

Are you over on Bimmerforums in the forced induction forum?

Cheers

[tmv]

Nice Imola 4.6iS and fun track car.
epsarks, those fenders look to be rolled and pulled to fit those wider wheels.

[PetrieJ]

Originally Posted by epdarks

Imola 4.6 = DROOL

I spy an intercooler on your E36. And your fenders look a little wider than stock

Are you over on Bimmerforums in the forced induction forum?

Cheers

Second. So jelly!


EDIT: Noticed you're in the Bay Area. Why haven't I seen you at any GGC Autocross?

[stupenduzzman]

Originally Posted by epdarks

Imola 4.6 = DROOL

I spy an intercooler on your E36. And your fenders look a little wider than stock

Are you over on Bimmerforums in the forced induction forum?

Cheers

The fenders have been massaged a bit, still only fitting 255s though. Going with Hard Motorsport rivet on flares as soon as the new turbo is on. I am on BF.C with the same username and do browse the FI section. I lurk mainly, don't post too much.

Originally Posted by PetrieJ

Second. So jelly!


EDIT: Noticed you're in the Bay Area. Why haven't I seen you at any GGC Autocross?

I did 2 auto-x with GGC last year but got yelled at for drifting. My car doesn't really fit into any classifications where I can be competitive so I mainly stick to track/drift days. Will hopefully be at either the NASA Thunderhill day mid August or the GripDriftSkid event at the end of August also at Thunderhill.