Trip computer inputs from ECU?

[newsh]

I have a couple of strange issues appear on my 3B.

First off the battery will go flat if left for a few days yet if I switch off, disconnect battery and introduce ammeter between terminal and cable and then lock the car there is no more than 3 or 4 milliamps flowing, presumably for the clock.

A possibly related symptom is that when switching on the ignition in the morning after zeroing the hour meter the night before, the hour meter will show 8 or 10 hours, ie the car thinks I've been driving all night, so something is definitely staying powered up.

Lastly (at the moment lol) The trip computer has stopped showing the average readouts, they both show 0.0 and the MPG reads 200 on the throttle and -- -- -- off the throttle.

I have been looking at the circuit diagram but not sure which signal I should be trying to trace and where to look for the A23, 27, 42, 45 connections might be found. Also if there's an obvious connector which may have come unplugged!

Any help here would be greatly appreciated!

Circuit diag below

http://www.s2central.net/S2_Schematics/B/B33.PDF

[Error404]

Have you checked the trip computer plug? That will cause some of those issues with the average readings if its a loose / bad connection. I believe the yellow connection under the dash that feeds the TC with fuel consumption info would cause this if its a loose or bad connection.
Not sure about the the others though...

[newsh]

The yellow plug in the back of the cluster? I'll have a look again in daylight.

There's also a couple of of connectors on the aux relay carrier? T5 and T10?

[newsh]

Anyone care to comment on the battery issue?

Or the Trip issue? Bearing in mind the symptoms, which signal is most likely to be missing?

[prj]

I would say perhaps the vehicle speed signal is missing...
But you really need to take a scope and look, it is hard to say otherwise.

It is completely possible you have a cold joint inside the cluster as well.
You need to troubleshoot it from the basics.

[Error404]

The yellow plug in the back of the cluster? I'll have a look again in daylight.

There's also a couple of of connectors on the aux relay carrier? T5 and T10?

yellow plug is on the trip computer loom, plugs into the mess of wiring around the fuse board, feeds the trip with fuel consumption signal from the ECU afaik

[newsh]

Cheers chaps.

I've tried 2 clusters, same symptoms with both.
The 2 lines to the ECU buzz all the way through from the cluster (one on yellow and one on black plugs), via the 10 and 5 pin black connectors at the Aux relay panel to the ECU connector. These are the Engine Speed and the Consumption Signals.

The Speed signal I can buzz from the cluster to the Aux relay carrier but I'm unsure or where it goes (or comes from) from there? I dont recognise any of the possible destinations in the diagram.

Speed signal wire is white and blue..

[newsh]

Hmm, actually the speed signal on the white /blue wire is an output, so if the speedo is working then the speed signal should be in the cluster and available to the trip computer. So maybe the ECU has stopped outputting the consumption figure?

[prj]

Well, you will need to measure on a working car.
I don't see why it would stop though.

Also, "buzzing through" gives a very little idea. You wold not be able to detect a short like this.

You need to run the car and monitor the signals with a scope.

[newsh]

Had a scope on it today. Can see the "consumption" signal appearing at the back of the cluster, looks to be approx 3v pulse changing width with the throttle. Is this voltage good?
Speedo is working so the road speed signal must be there. What am I missing here?

to recap
Its the same on 2 different clusters
MPG readout is 23.5mpg at rest and 200mpg when moving with the throttle open, -- -- -- when moving with the throttle closed. (The car knows it is moving so speed sig is present)

What other tests can I do?

[newsh]

Ok (having pondered in my sleep) from the symptoms above it would appear that the "consumption" signal is not actually getting seen by the cluster. The car knows it is moving but thinks it is using no fuel hence immediately reading 200mpg. As PRJ suggested I'm going to try and look at the signal on another car to see what it looks like.

[prj]

Yeah, compare them.
If it is the same, then you need to inspect the cluster electronics for cold joints.

[porkkis]

Speedo may work even if the speed signal is not getting anywhere from there.
Does your diff lock turn off automatically? Have you recently made any radio installations and plugged the white/blue speed signal wire somewhere it should not go?

[newsh]

Porkis. The blue/white wire is not connected at the radio, I checked that already (and again just now)

But the diff is not disengaging automatically!

[prj]

If it's not disengaging automatically either the wire going to the diff is cut, or you have no speed signal.

Did it use to disengage automatically before?