Thoughts on a Transmission Issu

[knfxda]

I have a 2001 4.4i and for some reason, I decided to top off with 89 Octane (10 gallons), today. I normally run 93 Octane, but wanted to see if a "blend" of the 2 would be noticiable.

The engine runs fine, however within 10 minutes of doing so, the transmission is now shifting late. I never run it in Sport mode, but it feels to me like it is stuck in Sport Mode. Shifts are not occurring until about 4k rpms. Downshifts are also late to the game.

I tried Sport mode and there was no noticeable difference or improvement. I tried manual mode and it still appeared that the "software" was overridding my choices. I would shift into 4th, but it would not shift and then indicate 3rd.

I've only driven about 15 minutes like this and given the roads that I was on I was not able to push it beyond 4100 rpms in 3rd to see when/if it would shift into 4th.

I've had no problems otherwise with the trans. It does have 115k miles on it and I have not changed the trans fluid (nor did the prior owner, I suspect - given the state of all of the other fluids that I have changed).\

Honestly, even with the high miles, the trans was one of the factors that I used in buying the X as it was so smooth and appeared to have no issues.

Could 10 gallons of 89 octane really affect sensors to the point that the trans is acting this way?

Open to any thoughts or suggestions.

thanks!

[upallnight]

Well with lower octane gas the knock sensor will tell the computer to retard the timing so that the engine won't self destruct. So yeah, lower octane can affect the way the trans is behaving. Next time put back premium and see if the problem don't go away.

[epdarks]

I personally would think the 2 issues are unrelated.

Either way, you are on borrowed time at 115k miles. A trans replacement is likely in your future.

[JCL]

Originally Posted by knfxda

Could 10 gallons of 89 octane really affect sensors to the point that the trans is acting this way?

No, not from the resultant 91 AKI octane rating (half 93, half 89).

But if that fuel contained water or too much ethanol, then that could potentially impact drivability. I would expect more engine symptoms in that case, though.

Given that it is not shifting properly in steptronic mode either, it sounds much more like a transmission issue than anything external.

[knfxda]

Well, I applied the infamous BMW fix...

I parked the car and turned it off. When I went back to it later, all was good. As if nothing happened. Transmission felt the same as it did previously.

I may be wrong here, but I get the sense that the BMW "compeuters" will sometimes get "confused" and a simple turn the car off and turn it on again seems to reset everything.

Now my problem is that swapping out the transmission fluid was the last thing on my list and I'm worried about doing it, now.

I plan on doing it in 3 weeks or so. So, if I don't see any other symptoms between now and then, I'm going to go for it.

Here's hoping I don't regret it!

[knfxda]

I forgot to add - the only other thought that I had was that CPU took somthing I did as "aggressive" and it "learned" that I wanted to drive aggressively.

After shutting down the vehicle, it unlearned this and went back to its normal programming.

That is the only thing that makes sense.

It really didn't feel like a "transmission" problem (in the sense of gears/clutches/moving parts and the like). It felt like a cpu problem. It seemed to be running a different profile than normal. There wasn't any slipping, hard shifts, clunking, etc, or anything that you would normally think of as mechanical problems.

[RRPhil]

One possibility : The transmission has a 'cooling strategy' mode which is activated automatically by the ECU if the transmission fluid temperature is unacceptably high. In this mode, upshifts are inhibited to deliberately maintain high engine speeds and therefore oil pump speed (and hence flow through the cooler). If you have a laser IR thermometer it might be worth pointing it at the transmission sump pan next time you get this problem to see how hot the fluid is getting.

On Range Rovers (same engine & transmission) this problem is very common because the bottom eight rows of the main radiator, which provide the cooling water to the transmission oil cooler, become blocked with sediment over time and stifle the cooling flow. I'm not sure whether or not the E53 cooling setup is the same?

Phil

[SlickGT1]

We have just been graced by RRPhil. Awesome.

Phil, have you finished the ZF6 speed rebuild? I have a few valve body questions on the 6hp26 and it delaying reverse engagement for up to 3 seconds, occasionally after a lot of stop and go traffic.