What's this connector?

[simonsimoff]

Can anyone tell me what this connector is for please? It's hanging down from the plug for the ECU on my 325se.

Although it doesn't appear to be used on my car, I'm just curious what it's for.

I've got the problem with my rev counter not working and I'm tidying up the wires which have been messed about while I look into that.

[asmith88]

iirc is for the obc, im assuming you havent got one?

[simonsimoff]

I do have the OBC fitted - when it works, as it's out of action with the rev counter at the moment - although it doesn't have any cables going near that connector.

[simonsimoff]

Hmm, OK thanks Will. I don't have aircon and my car's a manual so I guess I can ignore those.

No my economy gauge and rev counter still don't work. It looks like a popular problem from what I can see in the forum.

My SI board batteries are fine, fuse 10 and 21 are OK, I have power to the torch charger, and I've tried a couple of other gauge clusters which didn't show any life either.

The next step, from what I've read, is to test for continuity between pin 6 of the ECU and pin 7 of the blue plug going to the gauges. I've got the diagram in the Bentley manual that shows me which is pin 7 on the blue plug, but I don't yet know which is pin 6 on the ECU so I was looking that up.

[Brianmoooore]

If you look into the face of the ECU plug, you will see that the pins on the end of each row are numbered, albeit with a very small typeface.

[simonsimoff]

Thanks Brian. I'll look the plug in the face first thing in the morning when I have some daylight.

[simonsimoff]

Good morning.

I just checked pin 6 of the ECU plug with pin 7 of the blue plug and I do get a connection.

Any suggestions as to what else it might be?

[Brianmoooore]

First thing we need to know (and this applies to all of you, with all faults!) is:
Has this fault been present since you have owned the car?
Has this fault occurred since work has been done on the car?
Has this fault occurred since the car has been laid up for some time?
Has this fault simply appeared suddenly in the curse of normal use?

[simonsimoff]

I've had this car for around nine months. The rev counter originally worked.

The car had another engine swapped into it in September which was like for like - another facelift 325 engine into what is a facelift 325se.

The rev counter worked at that stage too and suddenly gave up two or three weeks later.

[simonsimoff]

The car is used daily, but the engine that went into it had been laid up for at least six months.

[Brianmoooore]

The rev counter pulse is generated by the ECU, goes along the black wire you've checked, and is fed to the rev counter electronics on the SI board in the instrument cluster.
Most common cause of rev counter failure is SI board batteries going short circuit, followed by a poor connection along the black wire.
In spite of your positive continuity result on the black wire, give pin 9 of the C101 engine loom connector some attention, where it passes through.

[simonsimoff]

I gave pin 9 a quick clean but there's no change. It looks very clean inside C101 - no signs of any corrosion or any water getting in. I double checked the connection afterwards and it's definitely getting continuity across that pin.

[Brianmoooore]

I gave pin 9 a quick clean but there's no change. It looks very clean inside C101 - no signs of any corrosion or any water getting in. I double checked the connection afterwards and it's definitely getting continuity across that pin.

That really only leaves the engine ECU and the cluster as possibilities. If your multimeter has an AC volts or frequency functions on it, you may be able to detect a signal on the black wire. I would expect a frequency of around 40 Hz at idle to around 350Hz at rev limit, but I've no idea what sort of voltage to look for.

[simonsimoff]

Yes, it's strange because I tried the other two clusters to no avail, and I also swapped over a spare ECU yesterday briefly just because it was a quick thing to check but it made no difference either.

I'm thinking of trying to get my other E30 running - I'm hoping that just has a flat battery from being sat a while - then I'll try the clusters I have in that to see if I can rule those out or not.

[Brianmoooore]

Unlikely, but worth a shot: You checked the black wire for continuity, and it tested OK, but try checking it for resistance to earth as well, with both ends disconnected.
Another zoner had a problem last week which turned out to be an internal loom short circuit, probably as a result of one particular wire being fried, when the main engine-body earth strap came adrift.

[simonsimoff]

Thanks, I'll check that too. It'll probably be next weekend now before I get a chance to look again.

I was hoping it would be something adrift like that when it first went because I've already had to fix a number of other issues on the car due to similar problems - two jubilee clips loose and missing on coolant hoses, and a couple missing from a fuel hose leaking fuel, and a loose vacuum hose...

I took the radio out (since the rev counter died) because the wiring for that was a mess, and the same with the alarm.

It's been a case of trying to fix one problem each week.