Hi, I was wondering anyone has an idea what could be causing the problem with my mk2. I converted my golf a while ago which now has an abf on carbs with a stand-alone ignition unit. I sorted out the rev counter by using the diode and resistor setup which works absolutely fine. However, when I apply electrical load, i.e headlights on, blowers etc the rev counter drops to almost 0, and bounces. As soon as I remove the electrical load, so nothing turned on it goes back to working fine. The rest of the clocks, i.e indicators, clock, fuel and temp all work fine, it just seems to be the rev counter. Thanks in advance.
Hi, I’m pretty sure the schematic was as follows: a and b coil wires - each into a 1N4004 diode and then both are spliced into a zenor diode. I actually don’t have a resistor in this circuit, not sure if I should or not ? So it’s powered off both the coil wires, and then, goes into the normal rev counter wire after the diode setup. Do you think it could be a bad earth ?
I found this schematic, which is pretty much what I used. I have read online that putting resistor to ground after the zener can help things, do you think this could help ? Or is it possible I need a smaller zener diode ? It’s just odd that the rev counter works perfectly and then as soon as you add the additional electrical load it starts to drop and bounce erratically.
Well, first of all I also don't understand why this is influenced by other users that just use 12V from the battery when you only have the setup to the rev counter coming from the coil. Adding the resistor will be a safety to decrease the current. But what kind of coil do you have? I suppose it is a DIS coil, right? Can't you use the output from the ECU?
Yeah I am using a wasted spark DIS coil, I think it’s from a ford mondeo/ka. I couldn’t use the tach output from the ecu as I tried connecting it to the clocks but it didn’t work and the manufacturer stated that it would only be compatible with more modern clocks. Initially I was running a distributer and abf coil, and just tapped the tacho wire into one side of the coil and it worked great. But as I’ve gone for the wasted spark set up, most of the ecu manufacturers state that using the diode set up above is the only method for making the rev counter work on older vehicles.
That's why I build the signal amplifiers I do get how the diode setup should work, but why you have the problem when a load is added I honestly don't know. I also don't like the idea of tapping off on the coil, but that's probably just in my head. I already sent one of my amplifiers to Tony. It's not so expensive to send it to the UK, so if you are interested, let me know, I'll build one and send it to you
could just be a bad earth. if its a CE1 car with MFA there is a male spade on the cluster loom, from here there should be a female spade with wire off to the side of the head. easily missed when loom is converted. Can just run a wire from this to the earth claw worst case
Thank you both for your reply’s. I’ve got a ce2 loom non MFA, so no earth to the head that I can see, I traced the loom back from the clocks and into the fuse box so I’m guessing it just earths through a common earth on the fuse box on a ce2 ? Do you think adding the resistor to the diode conversion would make any difference ? Also, on initial start up for a couple of minutes this morning, putting the lights/fans on had little difference, so I’m starting to think that maybe it might have something possibly to do with temperature ? Could it be the regulator on the alternator failing when getting hot, which would then cause a voltage drop and when applying extra load, the coil wires aren’t getting a steady 12v ? I measured the voltage across the battery this morning, which was around 13 volts with everything turned on, I might try and get the car hot later and see if it drops below 12v. Do you think this would then affect the rev counter if so ?
alrighty no extra earth for you then, its just got the one earth to the internal earth bus in the fusebox if it was an issue with voltage I'd expect engine running to be affected at the same time, you could try wiring in that resistor (pull down resistor) but if it was that I'd expect it to be a problem all the time not just when hot also... in theory going off the coil negative terminals should be fine, I mean thats how all petrol MK2 are from the factory after all. But if the ECU has a dedicated rev counter output I'd rather use that with an adaptor, I'd assume you can use the same unit as the 20v boys do
Do you have any other lights (leds) dimming or not working properly on the dash, when turning on headlights, blinkers etc?
