Info on Instruments wanted please.

UK forum for general and technical discussion about the Z3 roadster

Moderator: Gazza

Post Reply
Bumpa
Joined: Fri 23 Jun, 2017 21:31
Posts: 50

  Z3 roadster 2.2i

Info on Instruments wanted please.

Post by Bumpa » Fri 25 Jan, 2019 17:36

I have a 2002 2.2 Sport. There are two things regarding the instruments that I wanted to ask about. The first is that the speedometer reads too high. I know most cars over-read a bit, but my Z3 is around 11% high. For example, when the TomTom shows a steady 70 mph, the speedo reads 80.

The second thing I have only just discovered after owning the car for 18 months. It has always had a small illuminated dot on the mileage display. I have just found out that this is the anti-tamper dot, which I believe shows that something has been done to the instruments in the past. I read that there is a procedure for getting the dot to go out, but I wonder if I do that will I risk the recorded mileage being altered? I have a fear that the car has done many more miles than the recorded 80K, and that someone has perhaps changed the coding chip or something else to get a lower reading. Is that a possibility?

Why do you think the speedo is so inaccurate? Could this all be related? One other thing, the other day I started the car and the rev counter didn't work. I switched off and restarted and everything worked as normal. That fault has not reocurred so far.

I hate electronics!

User avatar
Gazza
Site Admin
Joined: Tue 04 Oct, 2005 21:58
Posts: 9359

  M roadster S54
Location: Romford Essex

Re: Info on Instruments wanted please.

Post by Gazza » Fri 25 Jan, 2019 21:12

Mine is over by 8mph at 70mph, I’ve no idea why.
Thinking further, if the speedo is over reading would that mean the mileage is rising more than actual mileage ?
Tyre and wheel sizes are standard.

The dot could be due to the cluster being replaced, from memory the cluster checks with the ecu for a mileage match.
If a lower mileage cluster is fitted it will show the mileage of the original cluster that it replaced.

I am not the ‘all seeing eye’ so could be wrong :wink:

You could check the MoT mileage details online. https://www.gov.uk/check-mot-history
Gazza

"Understeer is when you hit the wall with the front of the car, oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall and torque is how far you take the wall with you"

Z3 S54 M roadster Image, BMW Z1, BMW M3 CSL, Z4M Coupe
ImageImage

Bumpa
Joined: Fri 23 Jun, 2017 21:31
Posts: 50

  Z3 roadster 2.2i

Re: Info on Instruments wanted please.

Post by Bumpa » Fri 25 Jan, 2019 21:59

Why didn't I think of checking the MOT history? Doh! I've just looked it up and the test results are there right back to 2006 and there is no sign of a suspicious mileage alteration. Well, that's a good thing anyway. perhaps, as you say, it had to have a new instrument cluster at some point in the last 17 years.

NZ00Z3
Joined: Thu 23 Jun, 2016 02:26
Posts: 70

  Z3 roadster 3.0i

Re: Info on Instruments wanted please.

Post by NZ00Z3 » Fri 25 Jan, 2019 22:17

In the E46 world, they have worked out how to re-code the instrument cluster to correct the speedo error. Unfortunately this is not an option for the Z3. Although the E46 guys have determined that there are two different speed calculations being used, 1 for the speedo with an "over estimate" factor and the one for the mileage recorded without the over estimation factor, so the mileage recorder is correct.

The easiest way to do a speedo correction is to install a box of electronic in the signal wire and add a correction factor. Something like the link below.
http://yellr.com/

The BMW dealer can remove the tamper dot. The higher recorded mileage will be the one used.

User avatar
Robert T
Site Admin
Joined: Mon 12 Jun, 2006 11:35
Posts: 10054

  Z3 roadster 1.9
Location: Cheshire

Re: Info on Instruments wanted please.

Post by Robert T » Sat 26 Jan, 2019 11:11

The speedo in the Z3 is deliberately set to read around 5-10% faster than you are actually travelling. When mine reads 70, the car is actually travelling at about 65mph by the satnav. I am not certain where they build in this "safety factor", but for the mileage not to be significantly skewed, I suspect it is at the gauge and not the speedo pickup. You can test this by putting the odometer into self-test mode and selecting speed display. You will then get a live readout of the speed sensor value in km/h, which you can then accurately convert to mph and see if it is the same as the speedo is reading and that of your satnav. Details of self-test mode are in the knowledgebase: viewtopic.php?f=18&t=20201

The tamper dot is illuminated when the mileage in the cluster and the mileage in the ECU do not agree. There is a reset procedure which will take the higher mileage of the two. I've not looked to see whether I can read both values with INPA, but I suspect it is something that it can do and then you would know what the two values are to see whether it is worth resetting or not. It might be that the car has had a new ECU, rather than a new cluster, which would result in the same dot.

Finally, the issue with gauges not working seems to be getting more common as the cars get older. There is definitely some fault detection built into the cluster and when a fault is detected, it shuts down the gauges to protect them. This doesn't affect the car, as the gauges are just there for the human to read - the actual signals are all digital and converted to analogue just to drive the gauges. I have an issue with mine that every once in a while none of the gauges will work - turn it off and remove the key long enough for the immobiliser to cut in and all will be well on the next start - this happens on average about once a year, so it is too intermittent to diagnose.

Cheers R.
Arctic Silver '99 Z3 1.9 & Black '59 Frogeye 1275cc
Image

LaRy
Joined: Mon 12 Nov, 2018 17:47
Posts: 10

  Z3 roadster 2.8

Re: Info on Instruments wanted please.

Post by LaRy » Sat 26 Jan, 2019 12:18

Hi,
One simple thing that no one has mentioned so far. What about wheel size? If those have a smaller diameter than the specificated wheels for the car, it will of course show wrong speed.
According to some international standard for speedometers, those must always show higher speed than real speed.

Bumpa
Joined: Fri 23 Jun, 2017 21:31
Posts: 50

  Z3 roadster 2.2i

Re: Info on Instruments wanted please.

Post by Bumpa » Sat 26 Jan, 2019 12:27

Thanks all, especially Robert for that clear explanation. I must have a go at the self test mode. I've never tried to use it. I also wondered if you could get at the speedo setting through INPA. I have it loaded on my garage PC. Next time the Z3 gets into the garage I'll plug in and have a look. As for wheel size, it's a good thought, but my car has the 17" wheels it left the factory with.

User avatar
Gazza
Site Admin
Joined: Tue 04 Oct, 2005 21:58
Posts: 9359

  M roadster S54
Location: Romford Essex

Re: Info on Instruments wanted please.

Post by Gazza » Sat 26 Jan, 2019 12:45

LaRy wrote:
Sat 26 Jan, 2019 12:18
Hi,
One simple thing that no one has mentioned so far. What about wheel size? If those have a smaller diameter than the specificated wheels for the car, it will of course show wrong speed.



Cough cough :wink:
Gazza wrote:
Fri 25 Jan, 2019 21:12
Mine is over by 8mph at 70mph, I’ve no idea why.

Tyre and wheel sizes are standard.

Gazza

"Understeer is when you hit the wall with the front of the car, oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall and torque is how far you take the wall with you"

Z3 S54 M roadster Image, BMW Z1, BMW M3 CSL, Z4M Coupe
ImageImage

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest