brubix
Posts: 13
Joined: Thu May 22, 2014 9:49 am

REX little mistery

Wed Feb 07, 2018 5:03 am

I drive my i3 REX since August 2014.
In more than 70.000 km I tested the car (and the REX) in all kind of situations, and I think I know pretty well what I can expect. Honestly, I truly believe this is an amazing car, practically with no limits (if only the REX could offer a little more power and the tank a little more capacity, but this is another matter).

Not a single a problem so far, except the following, which appeared for the first time a few months ago (about at 60.000 km).

Highway on the plain, speed around 120 kmh, battery goes under 5% (approx.) and the REX turns on.
For 15-20 minutes the car slows down to a speed as low as 35 kmh up to 70 kmh maximum.
Then it can accelerate again even to the top speed, if the battery still has some juice.
Never had this problem before: the car always could (and still can) run at least at 120 kmh even when the battery goes to zero (except during those 15-20 minutes).

I would think to the ageing of the battery but what makes me really puzzled is that this happens only if the gasoline tank is full !
Same pattern, but with the tank at 3/4 and the problem doesn't occur.
In fact, the only thing that changes in those 15-20 minutes, is the fact the tank progessively empties from full to 3/4 (approx.)
Moreover, if I stop to refuel and resume the trip with the battery still very low (obviously) the problem doesn't occur a second time.

Here a you can see a few pictures of what the display shows when the condition is "active":
https://drive.google.com/drive/folders/ ... NNq0b3Pwb5

Local service has already checked the car and got in touch with the country headquarter's engineers but all they could offer are a few silly explanations that do not explain the observed behavior.

Any thought?

tjburbach
Posts: 50
Joined: Fri Oct 13, 2017 7:28 am
Location: Austin, TX

Re: REX little mistery

Wed Feb 07, 2018 3:26 pm

This sounds a lot like the state of charge issue that some others have run into where the i3 is not correctly measuring the condition of the battery. Here is an article about it with the related service bulletin numbers. However it does seem odd that the service technicians would not already know about this.

http://bmwi3.blogspot.com/2017/03/incor ... dings.html
-Tim

tjburbach
Posts: 50
Joined: Fri Oct 13, 2017 7:28 am
Location: Austin, TX

Re: REX little mistery

Wed Feb 07, 2018 3:42 pm

I rushed to reply after looking at your photos but reading the post again in more detail the failure you describe is different than the state of charge. I wonder if your failure is related to the fuel tank pressure sensor causing the Rex to not run at the rpm required for the speed you are driving. Then after the tank gets to 3/4 full and you depressurize it to fill the tank up the sensor works correctly, for some amount of time. One experiment I can think of would be to get into the failing condition with a full fuel tank, then stop and use the pull handle to manually depressurize the tank and open the tank fill cap. Close everything up and try running again to see if the behavior changed.
-Tim

tjburbach
Posts: 50
Joined: Fri Oct 13, 2017 7:28 am
Location: Austin, TX

Re: REX little mistery

Wed Feb 07, 2018 4:08 pm

I was looking over the Rex document thinking about this some more. The technical documents mention that the Rex goes through a warm up cycle that can last up to 360 seconds at up to 2400rpm (the speed it would normally run to maintain a vehicle speed of 50km/h).
In order to bring the combustion engine and the catalytic converter to operating temperature, the
combustion engine is operated at a speed of 2,200 rpm - 2,400 rpm during the warm-up phase
(5). This is dependent on the speed driven and, at the same time, represents the idle speed of the
combustion engine. The period for this warm-up phase is roughly 360 seconds depending on the
ambient temperature
The graphs imply that as the state of charge falls the Rex rpm should increase in order to make power to charge the battery. One possibility then would be that the Rex is staying in the warm up cycle (the system believes that the SoC is high enough to spend time warming up the emissions system). Another possibility is that the Rex thinks the ambient temperature is too high and is reducing rpm in order to attempt thermal management control. What is the current weather conditions where you are driving?
-Tim

https://attachments.priuschat.com/attac ... Engine.pdf

brubix
Posts: 13
Joined: Thu May 22, 2014 9:49 am

Re: REX little mistery

Wed Feb 07, 2018 10:45 pm

Thank you for your interesting remarks.
I forgot to mention that BMW already replaced the tank sensor.
It always happened in mild (or not-so-cold) weather. Last time must have been around 5-6° Celsius, but before it certainly happened in warmer days.
What I find really puzzling is the "full tank" factor. I definitely try your suggestion to manually depressurize the tank and I'll report back (although it will take a few days since I'll be traveling [by train !] in the next days).

brorob
Posts: 104
Joined: Sat Oct 31, 2015 5:53 am

Re: REX little mistery

Sat Feb 10, 2018 9:12 am

I wonder if something is malfunctioning with the thermal cooling system for the batteries. The batteries could be getting too hot then cooling down to a normal operating temperature during the reduced speed duration which would give you full power again. The reason I suspect this is when it was really cold out and I just started driving, without any departure time or preconditioning, my power band would only show a few bars until the batteries warmed up from driving. Could be just the opposite happening to you.

Would be interesting to see the battery packs temperature when this happens.

brubix
Posts: 13
Joined: Thu May 22, 2014 9:49 am

Re: REX little mistery

Sun Feb 11, 2018 12:06 am

Is it possible to see the temperature of the batteries ?

alohart
Posts: 2121
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: REX little mistery

Sun Feb 11, 2018 12:11 pm

brubix wrote:Is it possible to see the temperature of the batteries ?
"batterietemp" is item 14.05 in the Service Menu. Search for "service menu" to learn how to access it.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

brubix
Posts: 13
Joined: Thu May 22, 2014 9:49 am

Re: REX little mistery

Thu Feb 15, 2018 5:11 am

First report. Upon my insistence they checked again and this time they "calibrated a sensor" and "re-programmed the car", whatever this means. I downloaded my profile to a usb key and now I see <i-step>I001-17-11-543</i-step>, if this is the current version. Unfortunately I cannot tell which version I had before.
I've just made a short test in the same conditions (tank full, exhausted battery, speed > 100 kmh) and the problem did NOT appear.
Next week I'll make a second, more demanding, test on a longer trip, when I'll be able to drive the battery down to zero.
However in the past, the problem manifested right after the REX turned on, and the battery still had some charge (4-5%).
Thanks to everybody !

tjburbach
Posts: 50
Joined: Fri Oct 13, 2017 7:28 am
Location: Austin, TX

Re: REX little mistery

Fri Feb 16, 2018 2:04 pm

Hope the "calibration" fixes the problem so that you don't have to worry about it any longer.
-Tim

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