Rev counter faulty reading

[BazK]

Hi.

My car is a Ford Sierra 2.0 Litre d.o.h.c. The rev counter suddenly started showing about half what it should. I have looked for loose connections, etc, but found none. Any ideas what's gone wrong, guys?

BazK.

[inz]

:/ I have the exac same problem only tho my one is always like that.

[dr pepper]

theres a little black thingy at the coil with 2 wires from it, its a filter for the tacho, check the connections here, and maybe try another of a scrapper.
sean.

[inz]

Originally Posted by dr pepper

theres a little black thingy at the coil with 2 wires from it, its a filter for the tacho, check the connections here, and maybe try another of a scrapper.
sean.

Hi happy new year btw what if i say to u that i have a self made tacho i have a dashboard with tachometer connected.. to coil with out any filters + what dose this filter do? + do i really need it? :S

anyhow in short word’s my coil wire goes to -ve side of coil. with out any filters

[dr pepper]

would a self made tacho be a lm2917 ic and a few other bits including a meter?, or is it a unit from another vehicle.
the filter removes electrical noise and spikes from the signal largely caused by back emf from the coil itself, this can cause tacho readings to be out, often half or double actual, if your tacho isn't protected by zener diodes on the coil input, then its likely to be fryed.
when you said btw, did you mean brothers of the third wheel, i'm a member.
sean.

[inz]

Originally Posted by dr pepper

would a self made tacho be a lm2917 ic and a few other bits including a meter?, or is it a unit from another vehicle.
the filter removes electrical noise and spikes from the signal largely caused by back emf from the coil itself, this can cause tacho readings to be out, often half or double actual, if your tacho isn't protected by zener diodes on the coil input, then its likely to be fryed.
when you said btw, did you mean brothers of the third wheel, i'm a member.
sean.

Hi. no its a unit for another vehicle. for some other sierra. but the dude that made me this mod said that its done by getting a dashboard of another sierra with tachometer and 1 wire to coil. and no other stuff is needed. but i never thought and he never said that u need a tachometer filter and maybe can u give me a photo of 1 ( filter ) + are u 100% sure that its the case? + i am not sure that the tachometer shows exactly half due to that its winter now and i donno its like 0 or up to -5 in here. it should be like ~1500 rpm right? when its cold... but when i start it shows 500... so i am confused.

and now to the btw. btw is a short word for "by the way" )))))

[dr pepper]

i use the linux operating system for internet access and my poxy camera will not work with it, so i cannot send you a photo.
the filter is usually next to the coil (on cars with a tacho), its a lile black thing about an inch wide by 3/4 inch high by 1/4 inch deep, and it has 2 wires on it, one wire connects to the coil negative (the one that goes to the ignition module), and the other wire goes to the tacho signal wire, so the module is 'in line' with the tacho signal.
heres a trick if you want to check your tacho (works on most), on the tacho - connect the ground to battery negative and the ignition terminal to battery positive (so the tacho has power), then connect your battery charger negative to the battery negative, but dont connect the charger positive to the battery, connect it just to the coil signal terminal on the tacho (without still being connected to the coil of course, the charger pos just goes to the tacho), your tacho should read exactly 3000 rpm for a 4 cyl unit.
sean.

[inz]

OK here it goes. so far what i know
The Instrument panel ( i called it dashboard ) or somebody would say clock on some forums has 1 green wire the one that we get the signal from coil. his number is 11 ok there are two types of schemes i will show you 1st is the up to 1987 year / 2nd is from 1987 to 89 now on the last one there is ur so called coil filter ( @ scheme its called "suppressor" )
and on the 1987 model there is no suppressor. but now the part that the green wire goes not only to coil -ve side but it has to be connected to ignition module ( on scheme called ESC II ).

Now i can try connecting my green wire to ESC II but what will that give me? will it fix the faulty reading? or i can try fucking this Suppressor and adding it. but still if i get suppressor i still have to connect the green wire to ESC II

the under the hood photo



The up to 1987 year scheme



the from 1987 to 1989 year scheme

[dr pepper]

ok, i tried to understand your explanation, the tacho taps off its signal from the coil, so you will have a wire from the ign module to the coil and then the same wire goes to the tacho signal input THROUGH the suppressor.
on the relative drawing S110 is a connector at the side of the coil, one of those little round rubber thingies, once you find this you'd tap one of the 2 wires from the suppressor to it (without breaking any original circuits), and the other wire from the suppressor to the tacho signal input (try the filter both ways round).
you could try just connecting the signal terminal on the rev couter direct to S110, but i wouldnt advise it as you could knacker the ign module.

my opinion is that the tacho ford use on some of their cars is a unit with a digital input, these are designed for the signal to come from an ecu or ign module directly, but to save cash they have adapted this type of tacho to work straight from the coil (with the filter to adapt the signal), but that is just my opinion.

incidently, i'm looking for a ignition system drawing for my sierra, its an 1800 cvh carb 1990, any chance you could post it on this thread if you have access to it, i intend to take the engine out of this sierra and fit it too my jeep kit car, so i want to strip out only the wires from the loom that are for the ignition system.
yes i know i'm a sierra killer

cheers, sean.

[inz]

Hi. anyhow today i wanted to watch what’s under the hood but forgot and not its to dark :< but i believe that if i am not mistaking i already have a wire from ignition module ( ESC II ) connecting to my coil -ve side? but how can i try to fix this stuff to work with out suppressor coz the old module were with out suppressor ;/ and maybe i have an old
moudel vers? + do u know what this wire dose that goes to ignition modulo maybe if the modulo is broken itself? :S or different tachometers can have different coil's? or maybe there is a different between the old instruments panel that work’s with out the suppressor and the new once?
i can show u a photo of what’s inside my instruments panel.

anyhow about ur ignition scheme its on the 1987 to 1989 picture just the right of my green box look closely there is 1.8 CHV sign if u want more schemes give me ur email and i can email u all that i have.

[dr pepper]

yep i realise the drawing is for my car cheers.

if your car starts then the esc module is fine, at least on the green wire coil output.
yep the green wire does go to the dash clock cluster, even on cars without an original tacho.
i was thinking all along that you were 'side fitting' a sierra tacho, but i've realised you said an aftermarket tacho, most cheaper ones are designed to be connected directly to the coil, and you could do that and it'd work fine without the 'filter'.
expensive ones are sometimes designed to be connected to an ecu, my mini has a drag-n-tach rev counter that will only work with an ecu output.
look at your tacho and see if theres a manufacturers name and a model number, i'll try and find out something on it for you.
p.s. does your car have 1 coil and a distributor, as far as i know all dohc's have, if your car has 2 coils and no distributor like most newer cars then that certainly explains why you're getting half readings, most after market tacho's are designed for single coil 4 cylinder engines.
sean.

[inz]

Originally Posted by dr pepper

yep i realise the drawing is for my car cheers.

if your car starts then the esc module is fine, at least on the green wire coil output.
yep the green wire does go to the dash clock cluster, even on cars without an original tacho.
i was thinking all along that you were 'side fitting' a sierra tacho, but i've realised you said an aftermarket tacho, most cheaper ones are designed to be connected directly to the coil, and you could do that and it'd work fine without the 'filter'.
expensive ones are sometimes designed to be connected to an ecu, my mini has a drag-n-tach rev counter that will only work with an ecu output.
look at your tacho and see if theres a manufacturers name and a model number, i'll try and find out something on it for you.
p.s. does your car have 1 coil and a distributor, as far as i know all dohc's have, if your car has 2 coils and no distributor like most newer cars then that certainly explains why you're getting half readings, most after market tacho's are designed for single coil 4 cylinder engines.
sean.

nonono u got me wrong i am using an SIERRA REV COUNTER instrument panel, from anothere sierra and by default i didnt had a green wire go to my dashbord. i had to make 1 myself. my car is 2.0 carburator. with 1 coil and a dsitrubutor and btw wich wire goes to distrebutor the high voltage one? or somth? or the same -ve side :S and in the sierra case the ECU is ESC II right? or i dont have an ECU :S

[dr pepper]

ok then.
dont connect to the high voltage on the coil, the green wire from the coil negative goes to the rev counter with the suppressor in line.
it is odd that your car's a 2.0 and doesnt have a tacho, maybe the engines a transplant job.
sean.

[inz]

Well the car had old instrument panel like old car's from 1985 or something. but this suppressor thing. its just a radio interfearnce stuff, + i must get it, and what do u mean by not connecting the high voltage wire

[dr pepper]

nope the suppressor adapts the signal for the tacho to work properly as far as i know, if it does that, then you really need it, and it wont harm to have it even if its not needed.
i said do not connect the ht becasue the tacho works on the lt.
you should have it working by now, is this being a pain in the backside then?.
sean.