Manky Monkey Motors

Hi all, got to the point of wiring 😱 everything is good and working except the Rev counter. I cannot get it to work off the ecu. There are no points or coil, just a coil pack that goes straight to hot leads. Someone said wrap a wire around an ht lead. Anyone any ideas of how I can get this single wire to work ?

You lost me at "ECU"! :(

I lost myself 🤣🤣

Is it an old style that needs a loop of (coil points circuit) wire through it - ie 70's Lucas smiths? If so, and your ecu is a wasted spark systen you might have a problem. So first thing, is it the old type?
If not, then it will have a single sense wire which you could try wrapping around one of the plug leads - but you might find it reads double...
More info needed.

It is a modern system, the Rev counter is a digital read out style dash. It is a single wire job that attaches in to the system, I have tried various ways, but I’m not getting anywhere except peed off. Speedo works, fuel gauge is reading. All the lights indicators etc are working in this dash, but the revcounter seems to not wanting to play. I have found a little information that states you just splice it in to a wire on the spark management box, but, which one 😱 the electronics are fully adjustable to get a read out.

Its likely that the wire, like most kit on modern cars, is looking for a signal as apposed to induction. Depending on what its looking for it could be from crank position or cam position sensors. It could be that the wire you are looking at could be the signal from the ECU to the digital read out which is interpreted at the head end.
If you know what the harness was from then you may be able to work it out. I suspect it is signal out to the head end.
All supposition mind. I'm no expert. You need to determine what the cable is looking for or sending bearing in mind a single sensor or sender unit can control many items/parameters across the engine. The opposite can also be true. For instance my Saab has no cam position sensor. It continuously measures the resistance across each spark plug during each cycle and couple this with crank position sensor will give you accurate parameters and can tell which cylinder is malfunctioning and can correct fuel delivery to each cylinder.
A bit long winded but hopefully helpful  ;D

Thanks for the input 👍
I tried to find a signal, there is a cam position sensor with 4 wires, I may splice into them in the hope I can get a signal.

Unlikely it will be lloking for a sensor signal, they vary too much.
Try connecting it to one of the coil firing wires ( there would usually be a plus supply and two firing wires on a wasted spark system). This might give you a half rpm reading, but this is fixable.

👍 more splicing and soldering 🤣🤣 oh, I tried the wire wrapped around the plug, nothing. Brand new silicone leads but I cannot get a signal, I tried my clip on timing light and that didn’t work either but does on the bike 🤔

Connect to one of the switch wires on the coil. If the coil's a wasted spark it will have three, maybe four wires. Three makes it simple, there will be a 12V supply and two switches. Connect to one of these. You should have some options to callibrate the counter. In the case you haven't, and it reads low you might have to resort to diodes and connect to both switch wires.
Oh, to go back to the 3/4 wires, I don't recall what the 4th one does tbh.

👍👍

Phew😱 well, latest update on this. It seems I have a pulse ! And I need volts. Then my old boss baffled me with needing a pulse to volts converter, or maybe a transistor that will boost the voltage, we found a signal, notice the use of the royal we 🤣, so his oscilly thingyme, gave a pretty pattern but it’s between one and four volts, my old analogue tachometer gave a half speed reading. The rest is beyond me, lots of calculations, fag packet drawings and a promise he will be back, hopefully with the right wotsit. 🤣🤣 meanwhile down here in Plymouth, the Coppersmith retired is wandering the streets totally baffled, do I really need a stupid rev counter, been screaming the bits off engines for over 50 years, two strokes, four strokes, singles, multis. Diesels even. I know when the revs are there near enough, maybe just chuck it in the bin marked not wanted on voyage 😡

Your "modern" tach needs volts? I think not. It wants to read pulses.
Your old one works but reads half? Connected to one of the coil switch wires? Are you going to use this, assuming it read correctly?

I’ve given up on it for the moment. It’s beyond me.

I connected into every wire on the coil pack, but it reads 12 volts constant, I couldn’t find a signal but the old analogue one did pick up a reading on the white wire and was quite stable read out. On the wiring diagrams it shows a tachometer take off from the igniter pack that is the one that is measuring very low outputs. But the digital one doesn’t show any reading whatsoever. Google throws up a lot of failures by others.

Minimutly you are correct the rev counter needs pulse I have volts, so I’m told I need a volt to pulse transformer thing 😱

Hmmm, I wonder if you have an amplifier built in to your coil pack - one that takes a tiny signal from the ecu, then uses a transistor pair to switch the coil on and off? Can you scan the wiring diagram?
If this is the case it will be very difficult to make yor counter work. However, you say you"old" one works?
Need more info on both rev counters as well. Are you set on ditching the old one?

Ha, this is more complicated than you think, see copied post from one of the forums, yes there is an ignitor in the coil packs, which means it's going to be difficult, and maybe the wrong pack is fitted since the early ones are hard to find:

#13  Rev Counter Not Working: post #13 Martin Y
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Posted 10 September 2013 - 03:26 PM
If the tacho has never worked since you've had the car, it's possible someone has already replaced the coil pack and used the wrong type.

The original 1.8 like yours uses 4-pin coil packs and one pin on each of the two coils feeds the tacho. The '95 onward 1.8 gets its tacho pulses from the ECU directly and the 4th pin on each coil is deleted. But the early 1.8 has a quirk where if the ignition is left on without the engine running it can start to heat the coil and eventually burn it out. That means the 4-pin coils are rarer, more expensive and hard to find. You wouldn't be the first to find 3-pin coils had been fitted instead of the proper 4-pin type.
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