M42 Tachometer wiring help

[jaredmac11]

Im trying to make sense of the tachometer signal for my E21 M42 swap. I thought this was handled with pin 9 on the C101 but I am not certain.

The ETM makes zero sense for the tachometer, but perhaps it carries another name in the diagram?

Hoping someone is familiar with the ETM and has gone down this path already...

[vpilarrt]

While the engine speed signal does go through pin 9 on C101 there's a lot more to it. The ECU receives a signal from the engine speed sensor (located on the bottom of the engine adjacent to the toothed ring on the front of the crankshaft) where it "processes" it and sends it to the service interval board in the cluster (pin 7 of C1). After more "processing" the now 4 "signal" lines connect to the tach through pins 1, 2, 3 and 4 of C4. I believe the engine code module also "processes" the signal. Use the '92 318ic ETM (its the most complete), see pages 1360-5, 6210-2 and 6210-3.

[jaredmac11]

Ah-ha.. unfortunately I was using the 92 318ic and looking at that same section; it was just all compacted and difficult to tell what was where. This is helpful though, I think I need to look at connecting to the ECU pin and not the C101.

I'll have to confirm. Thanks again, that was very helpful

[mikerunt]

bumping this old thread, and apologies if the info is elsewhere (searched and could not find). i am trying to wire up an aftermarket tach and looking for where to pull signal from. can anyone point me in the right direction?

[TobyB]

http://www.wedophones.com/BMWManualsLead.htm

from the '92 318ic manual (which seems to be the most accurate for the M42)

t

[mikerunt]

http://www.wedophones.com/BMWManualsLead.htm

from the '92 318ic manual (which seems to be the most accurate for the M42)

t

i wish i knew how to read and understand this!

[mikerunt]

http://www.wedophones.com/BMWManualsLead.htm

from the '92 318ic manual (which seems to be the most accurate for the M42)

t

[varg]

i wish i knew how to read and understand this!

So learn. It's not difficult. The BMW ETMs even have a key for what symbols mean, they are ideal for learning because they're impeccably laid out and readable.

30 seconds on google will tell you that E30 tachs accept a 12V square wave signal, one pulse per ignition event, which tells you what the ECU output to the tach is. So if your aftermarket tach (why? just use the OE cluster) takes that sort of input, you're good, just splice into the applicable wire. If it doesn't, figure something else out.