E30 Revcounter/Tacho question

Post Sat Jul 22, 2006 9:25 am

How is the tacho on an E30 driven?

Is it the same principle as a ford one where you have VCC, GND and Signal (Signal being a wire from the negative sie of the ignition coil)

Or is it an induction loop based system which picks up a trigger from one of the HT leads via a clip-on sensor?

Cheers

Post Sat Jul 22, 2006 9:38 am

It's driven directly by a signal from the ECU.

Not sure what the ECU uses to generate the signal, but probably the crank position sensor.

Ian.

Post Sat Jul 22, 2006 10:06 am

Cheers Ian

Does anyone know what sort of signal this is, frequency or voltage?

Post Sat Jul 22, 2006 10:53 am

Paulsimon8 wrote:Cheers Ian

Does anyone know what sort of signal this is, frequency or voltage?

Frequency. If I get a chance, I'll measure it and let you know exactly what the signal is.

Cheers,

Ian.

Post Sat Jul 22, 2006 1:35 pm

Cheers chap - you are a star

Post Sat Jul 22, 2006 1:40 pm

are you still having this problem? i would have phoned the garage to find out what they did to get mine working but were not really on speaking terms

Post Sat Jul 22, 2006 11:31 pm

yep, still having this problem, not a major problem, but still a problem

Post Sat Jul 22, 2006 11:40 pm

It goes from the ECU to the speedo on a black wire that passes through pin 9 of the C101 engine loom connector and goes to pin 7 of the blue cluster plug.

Post Sat Jul 22, 2006 11:43 pm

Cheers Brian

Whats the crack with the 6 cylyider and 4 cylinder chip for the rev counters

Post Sat Jul 22, 2006 11:53 pm

White coding plug pushed into the lower front right of the cluster.
6 pot gives 3 pulses per rev, 4 pot gives 2, so you have to tell the cluster which yours is.

Post Sun Jul 23, 2006 9:12 am

Cheers Brian,

I'll let you know what findings I have

Post Sun Jul 23, 2006 2:14 pm

Still having no joy with this

Altho, interestingly, is the signal from the ecu to the tacho a constant 12 volts with a varying frequency? or is it variable voltage?

Post Sun Jul 23, 2006 2:22 pm

Just guessing, but almost certainly frequency. It's very sensitive to a poor connection at the C101.

Post Sun Jul 23, 2006 2:28 pm

The C101 has been binned off as i've scrapped off the M20 engine ;) and fitted my YB cosworth lump.

The wire to pin 7 on the back of the insrument blue plug connected (via a removeable connection) to the original tacho output wire off the L8 ecu loom from the cosworth.

Only problem is, the cosworth standard rev counter worked off back emf voltage from the collapsing coil field - this was between 2 and 300 volts depending on the rpm, and then the tacho had a load of filters inside it to make this signal more useable.

bmw tacho's are not my strong point

If only Fuzzy knew how his worked, as it works properly he says

Post Sun Jul 23, 2006 2:31 pm

You need someone to put a 'scope on a standard E30 then, compare it with yours, and then get designing an interface.

Post Sun Jul 23, 2006 2:38 pm

Cheers Brian

Not everyone has an osciliscope kicking about tho

- expensive testing equipent

and it might be time to invest in some

Post Sun Jul 23, 2006 3:14 pm

Paulsimon8 wrote:Cheers Brian

Not everyone has an osciliscope kicking about tho

Some of us have

I'll try and take some measurements tomorrow.

Ian.

Post Sun Jul 23, 2006 3:44 pm

You are a GEM Ian - much appreciated

Post Mon Jul 24, 2006 12:14 pm

I've not taken it all the way through the rev range (neighbours wouldn't be too chuffed when I get to 7.8K rpm

), but here's something to give you a ball park figure.

At tickover, I was getting approx 40Hz at 5.95v RMS.

At 2k rpm I was getting approx 96Hz at 5.95v RMS

At 3k rpm I was getting approx 140Hz at 5.95v RMS.

From this you can see that the voltage is constant and it's just the frequency that's changing. Oh, and it's a pretty clean square wave signal.

The above measurements are what's coming out of my ECU, so they will be very slightly different to the E30 signal. I had to use a tacho calibration unit to get the tacho reading 100% accurate. Without this unit, the tach read approx 12% high at all rpm's.

Thinking about it, you may be able to use the same tacho calibration unit, as I think it can take a coil triggered input and give the correct signal for the E30 on the output.

Have a look at THIS

Cheers,

Ian.

Post Mon Jul 24, 2006 1:19 pm

Fantastic information Ian - i'll get onto my chap who is an electronics whizz and see if he can make a frequency counter or convertor

Post Mon Jul 24, 2006 4:32 pm

the tach just went out on my 1993 E30 cabrio.

all other gauges work, and the tach worked previous.....

where should i start to troubleshoot the source of the problem?

Post Tue Jul 25, 2006 2:33 am

robmpulse wrote:the tach just went out on my 1993 E30 cabrio.

all other gauges work, and the tach worked previous.....

where should i start to troubleshoot the source of the problem?

bumpidy bump bump

Post Tue Jul 25, 2006 8:59 am

robmpulse wrote:the tach just went out on my 1993 E30 cabrio.

all other gauges work, and the tach worked previous.....

where should i start to troubleshoot the source of the problem?

Black wire, pin 9 of the C101 enine loom connector.

Post Tue Jul 25, 2006 1:26 pm

Brianmoooore wrote:Black wire, pin 9 of the C101 enine loom connector.

WHERE DO I FIND THIS? THANKS FOR THE HELP, TOO.

Post Thu Jul 27, 2006 1:39 pm

Post Thu Jul 27, 2006 2:57 pm

Big, circular, black plug & socket on the bulkhead to the left of centre.

Post Mon Jul 31, 2006 6:38 pm

Chris-W wrote:Big, circular, black plug & socket on the bulkhead to the left of centre.

I have no idea what that means.... I am guess a language barrier....lol

oh, and I noticed last night that the MPG gauge is not working as well......does this change things? or could be the same problem?

Post Tue Aug 01, 2006 8:26 pm