Rev counter help please.,si batteries?

[Dlb26]

Hi all I am after some help with my rev counter /service lights
When switched off I have three green led's lit even when reset. If I start the car they remain lit and the rev counter works fine until 3000rpm at which point it stops working and the led's go out. If I stop the engine they come back on and restarting will reset the whole process with rev counter working up to 3000rpm.
I have checked si battery voltage including after 15mins in the freezer and get 3. 15 volts on both.

[Dlb26]

Sorry
Forgot, car is 1988 325i chromie

[Speedtouch]

Sounds like the batteries are pretty healthy, if they are giving 3.15V each.

[Dlb26]

That's what I thought

[Speedtouch]

Well, here's what the Zone Wiki has to say about it:

http://www.e30zone.net/e30zonewiki/inde ... ot_Working

Worth checking the C101 connector, by the sounds of it...

[HartgeH27]

Good shout Maurice.............

[Brianmoooore]

As already said, batteries seem good, but C101 problems aren't going to affect the resetting of the SI lights, so, unless you have two coincidental faults, I think you're barking up the wrong tree there.
3 volts on each battery suggests this is the later version of the SI board with Lithium batteries. These are considerably less reliable than the original version with AA sized NiCd batteries, and although I've never come across this particular combination of problems with one, I'd suggest trying a complete replacement board of either type.
Having said that, I wouldn't be at all surprised if, in the end, this turned out to be an alternator fault.

[Dlb26]

Thanks brian, I've had a quick look at the C101 plug and nothing obvious so you may be right and yes it is the later battery type. Not sure if it's relevant but I disconnected the main battery to play with the C101 plug and on reconnecting it has taken a while for the leds to come back on and I have the fifth one lit also (suspect no. 4 might be a dud led) rev counter didn't work at all during this time. Haven't had chance to run it since the lights were back on to try rev counter but I don't think I have changed anything as yet. I do have a spare si board from an eBay spare binnacle that has slight damage from using over long screws, not sure if it has cut any tracks, would any damage here effect the rev counter and service lights if I tried it as a test? Also economy gauge only ever worked with foot to the floor at higher revs but was like that when the rev counter worked properly.

[Brianmoooore]

Can't think of any screws that could damage the SI board, but even if tracks were damaged, the resulting symptoms are likely to be different from what you have now.
Any SI board that has been lying around unused for a while, inside a cluster is likely to have problems of its own. If it has NiCd batteries, then these are likely to have run flat, which shouldn't harm them if they were in good condition, but if they are several years old, they may have corroded and leaked.
If it has Lithium batteries, these will die in a few years if not switched off*, and are not rechargeable. Once run down, they need to be changed.

*Boards supplied by BMW as replacements for failed units had three pins and a jumper link, with a large orange arrow sticker pointing at it. Jumper link had to be moved from 'off' position to 'on' position before using the board. Boards fitted at the factory did not have the jumper pins fitted, but had a small wire link
soldered in place near where the two 'on' pins would be fitted. If storing this type of board, the wire link should be cut.

You say your car is a '88 chromie. I suspect this is the first use date, and the build date is somewhat earlier, since '88 cars should all be facelift.
There's a small possibility that your car sends the fuel rate signal (used by the economy gauge) and the engine speed signal (used by the tacho.) from the ecu to the instrument cluster by a small three pin plug and socket on short branches from the engine loom near the ecu and from the body loom near the instrument cluster, instead of via the C101.

[Dlb26]

It's a convertible, did I read somewhere that they had chrome longer? It's on an F plate and I've seen newer G plates for sale etc. The screw damage has come from two longer screws being fitted where the black surround is attached to the binnacle on the central of the four lower holes.

[Dlb26]

Partial success, I've put batteries (2.8v spares) in spare si board and tried it. Rev counter and econometer work great now however when switched off the rev counter needle sits at about 800 rpm, I could live with it but turning the ignition on brings it back to zero before starting. Service lights look like they are working properly, nothing when switched off, 5 lights with ignition and then go off when engine started. Unfortunately speedo now seems out of sync with actual road speed, it goes up slowly and won't go past 50. Unrelated problem caused by all my fitting and removing or related? I didn't think speedo and si board did a lot of interacting?

[Speedtouch]

Maybe worth trying a new set?

[Brianmoooore]

Partial success, I've put batteries (2.8v spares) in spare si board and tried it. Rev counter and econometer work great now however when switched off the rev counter needle sits at about 800 rpm, I could live with it but turning the ignition on brings it back to zero before starting.

Very common fault with the Lithium battery version of the SI board. Causes no problems, and doesn't affect the accuracy of the tacho. in use. I have no idea what the actual failure is at component level.

Unfortunately speedo now seems out of sync with actual road speed, it goes up slowly and won't go past 50. Unrelated problem caused by all my fitting and removing or related? I didn't think speedo and si board did a lot of interacting?

New one on me, but you're quite correct that there's no interaction between the speedo. and SI board.
All the speedo. electronics are self contained on the unit itself, and no connection to the rest of the electronics on the SI board, other than a feed of the road speed signal to the economy meter part of the SI board.

[Dlb26]

I have a spare, untested but I'll try it tomorrow, do any of the speedo wires go through C101 plug? Just wondering if I have caused it by opening it.

[Dlb26]

Solved, spare speedo has cured that little problem and all good again. I even have a working econometer that I never had before. Thanks to everyone that helped.