Rev counter 325i sport

[minimatan]

I bought a rev counter second hand and the idle sits at 2500rpm, rather than 1500.

Could someone please explain why this is and how it can be rectified, if possible, with the existing unit?

[Brianmoooore]

if we are talking about the rev. counter module from an E30 cluster, then probably the needle has been taken off and refitted in the wrong position.

[minimatan]

No it is the entire instrument cluster that I replaced. Are non-Sport instrument clusters differed to those for the sport?

[kam-325i]

all 325i clusters are the same.

Are you sure the cluster is from a 325i ? there is a coding plug on the clusters.

[Brianmoooore]

The only difference in clusters, except ancient ones, is the fuel gauge, which must be matched to the fuel tank size. There is a plug in coding module on the lower right front of the cluster, which sets the rev. counter for four cylinder or six cylinder cars.
As kam-325i is hinting at, the chances are you have a four pot coding plug fitted, which will read 50% high when connected to a six pot.

[minimatan]

Yes, I think that may be the answer as I am certain that the instrument cluster is not from a 325i.

So what should I do in order to endure that the rev counter reads correctly ?

[kam-325i]

remove the coding plug from your old cluster and fit it to the new cluster...

[minimatan]

I think that we have disposed of the old cluster

[kam-325i]

I think that we have disposed of the old cluster

Oh Dear.......

[Brianmoooore]

There's a good chance that you will need the fuel gauge as well. Why did you change the cluster?

[minimatan]

Because the batteries on the Si board failed meaning that the rev counter only ever worked after around 45 mins of the engine running if at all. So it seemed easier to swap the unit.

[Brianmoooore]

Well, you know different now. Plus the SI board batteries in the one you have fitted will also be on their last legs if they've never been replaced.
£2 each for a couple of batteries would have been a better bet, plus you could have attended to the 220 ohm resistor in the pad warning circuit at the same time.

[minimatan]

I did buy the batteries from Maplin but I simply cannot find time to do the job properly, considering that my soldering skills are non existent.

[minimatan]

An update for you gents further to your invaluable advice.

We found the cluster and fitted the old connector, but... it now indicates an idle speed of just over 1000, which seems a little high... any insights?

[Brianmoooore]

Someone been playing with the throttle stop? Throttle cable too tight or sticking?
Before getting too involved it would be a good idea to confirm that the rev. counter is accurate.

[minimatan]

Well, from a previous encounter on a surrey meet, I have been told that the throttle cable is routed incorrectly. The mechanic thought so too, but it is quite long so we couldn't see where else it should go. I'll ask one of the guys at tomorrow's Surrey meet.

How would one go about verifying the accuracy of the rev counter?