what should I know before buying a E89

[KennyP]

Originally Posted by RobbiZ4

The 2nd important task:
replace the 2 microswitches coupling lock in the boot every 10 years

What exactly happens if you dont replace these microswitches? How do they fail? And when they fail is it alot harder to replace them because boot lid, im guessing, would not be operable? Please explain why its recommendation nr:2 on your list and so important.

Im asking because i already have these switches but solved the issue i had. So im biased to not replacing these switches as they work fine... If i knew more about the risks it would motivate me to go ahead and replace them. Otherwise i would just put them on the shelf and replace when there is an issue with them.

[RobbiZ4]

The issues with these MS are very randomly, sometimes depending on humidity or temperature.

1) Sometimes one can here the malfunction when closing the trunk lid:
the trunk lid is already down, but the hydraulic pump doesn't stop or stops delayed up to 10 seconds. If that happens, the CTM interrupts it's operation due to the time difference between the left and the right switch.

2) Warning and gong while driving in the car without touching the roof
One of these MS changes it's switch status and indicates an open trunk lid to the CTM.

3) The trunk lid stucks or doesn't finalize it's intended operation
Wrong or lost signal from one or both MS.

On several of replaced and later on opened MS, I could see traces of corrosion inside of the black housing.

The risks are:
#1 you won't be able to close the roof anywhere on the road far away from home
#2 as it's not anymore operable, you can't open the trunk lid for any support or exchange of these MS
#3 the hydraulic pump might get very hot, as the CTM increases the operation time of the pump to finaly get the trunk lid closed

Statistics of the E89 roofs I've repaired in the past:
=========================================
40 % broken wires in the rear roof shell
40% randomly working microswitches coupling lock
10% broken hydraulic hoses in the rear roof shell
5% rusty hall sensors (HS) on the hydraulic cylinders in the roof shell (1 HS) as well as on the right coupling lock (2 HS), which will lead to wrong signals


5% other issues

With my EKG system I'm able to diagnose these upcoming faults in advance. The following measuring was taken on a stress test for these micros switches - only opening and closing the lid several times in a short period:
https://z4-forum.com/forum/viewtopic.php?f=23&t=129048



Both microswitches have to be opened or closed exactly at the same time. If there is a smaller or bigger time difference between left and right, the CTM will identify a rotary movement of the trunk lid, same as with those 2 microswitches in the rear roof shell.

If these time differences exceed an internal limit, the CTM immediately stops all activities and sends a warning.

In most cases, the resulting interferences are very surprisingly.


To replace these micro switches, you have to bring the trunk lid into it's vertikal position. If there is any issue, you can't operate the roof any more and you need very special tools.

In the following a pic of how to get acces on a coupling lock as well as the position of the microswitch (MS).

[surfwooder]

I'm a firm believer of lubrication of moving parts on a BMW. I own my 2009 BMW 3.0 Z4, and my wife owns a BMW 328IC, we bought in 2008, using Euro delivery. I inspected both and found no trace of lube on the Z4, and the 328IC. I wiped down all the seals and coated them with Gummi Plege. I notice a tighter seal on both cars. I opened and stacked the roofs and shot every joint with Wurth spray lube. All the noises stopped, and I timed the open close time, and found it came back into specs (22 sec on the Z) I look at every available wiring harness and saw only one wear point. I covered this point with friction tape, and noted the tape only after a few ups and down showed some rubbing. Here in the U.S. there is a effort by BMW NA to reduce the repair information available on later model BMWs. On the E89, very little is out there, even Bentley Publishers has no manual for the Z4. My 328IC E93 is supported but later models are not.

[surfwooder]

Originally Posted by KennyP

What exactly happens if you dont replace these microswitches? How do they fail? And when they fail is it alot harder to replace them because boot lid, im guessing, would not be operable? Please explain why its recommendation nr:2 on your list and so important.

Im asking because i already have these switches but solved the issue i had. So im biased to not replacing these switches as they work fine... If i knew more about the risks it would motivate me to go ahead and replace them. Otherwise i would just put them on the shelf and replace when there is an issue with them.

I agree with Robbi. Relays do fail. The weak part is the usually the relay coil, which is activated by the Convertible Top Module. The coils operate on 12vdc, low amps. The coil works like a magnet and pulls in the internal contacts that power the hydraulic motor. The voltage and amps for the motor come directly from the Battery Power Control Box. Internal to that box is a 50 amp slow blow fuse, to protect the motor. Should the motor become shorted and draws less than 50 amp, the contacts in the relays could become welded in the on position resulting in motor over heating, and finally motor failure. I have a 2009 Z4, I've changed the relays, and now I'm thinking of doing a amp meter test to check the draw of the motor during operation of the top. This will determine the health of the motor. I bought my Z 4 years ago, with no history. I also keep a log on all my repairs on both cars, this helps keep track on recurrent problems. These cars are complex machines, so record keeping helps a lot.

[RobbiZ4]

Originally Posted by surfwooder

Should the motor become shorted and draws less than 50 amp, the contacts in the relays could become welded in the on position resulting in motor over heating, and finally motor failure.

Unfortunately it's the oposite:
At first the inner relay contact can weld due to the high inductive load, when the motor stops. But if this welded contact can not open anymore, the motor will run continously until all plastic will melt inside of the motor. Have a look at the following pic of such a desaster:

Originally Posted by surfwooder

...and now I'm thinking of doing a amp meter test to check the draw of the motor during operation of the top.

We've measured about 37 amps on an E89. Might even be a bit higher for short moments when the motor get's shut off, but below 50 amps.

[Meonstoke]

Originally Posted by RobbiZ4

The most important thing is, getting the 2 salmon relays replaced every 5 years to avoid an expensive damage of the hydraulic pump.

The 2nd important task:
replace the 2 microswitches coupling lock in the boot every 10 years

Hi Robbi,

This reads as a good precaution to take when purchasing an E89. Thanks for sharing your advice and insights.

M.