Lost Spark

[sj-bradley]

You may have 12 volts there, but putting a heavy load like a lamp will cause it to try and draw too much current.

 

Measure the volts after you connect the lamp and you will find it nearly at zero volts and the lamp "grounds" the voltage out.

Put the meter in series with the lamp and see how much current is being drawn and you will find very little - not enough to light the lamp. A 5 Watt light will need just under 1/2 amp to work otherwise it's just a short to ground.

 

Simon.

[agent_zed]

hmm. The haynes manual says though to connect a 20w bulb between the LT connections without the coil connected and crank the engine and the light should go on and off. I figured 5w's should be ok. What does the coil need normally? does the current change when cranking?

 

although i suspect the dizzy is not providing the switching to tell the amplifier module to turn on and off as it didn't do anything when i tried.

 

maybe i'll just replace the dizzy and see if that works and then the module failing that. And if that doens't work god knows what is wrong as that will be pretty much everything replaced.

 

The annoying thing is that for the past 7 years she's started on the button everytime. She was running fine febuary time.

[sj-bradley]

If you measure the resistance of the coil ( Low tension side - not plugs).

 

You will get a low resistance 1 or 2 ohms which mean that it will take 6 - 12 amps each time the coil is grounded.

That is why Haynes recommend a 20 Watt lamp as this needs about 2 amps to light up.

 

The lower 5 Watt lamp will only let through 1/2 amp which means the coil may not produce a big enough spark at the plugs as the primary is limited to a max of 1/2 amp when it really wants much more.

 

Also, the frequency at which the lamp is switched may also mean that the average power seen by the lamp will not be enough to light it up either.

 

Also - as the coil is an A.C device when working, the impedance at engine revs mean that the effective resistance (impedance) will be higher than the short circuit calculations imply.

 

Simon.

Edited May 29, 2014 by Simon B

[Guest mark little]

I'm just heading for the garage to get mine sorted, put the new coil on tonight, still no spark and after reading the other posts above I know it's beyond my limited knowledge

[nigelt]

You say you have put a bulb across the live feed and ground and that it fails to light up. It could be that there is a resistor in this live feed that limits the amount of power to the coil pack and to the amplifier. Effectivly avoiding a short circuit when the transistors turn on in the amplifier. If this is the case, the 12v will be dropped across the resistor and there won't be any volts left to light the bulb.

 

I am not familiar with the pinto setup, so the above is only a suggestion.

 

You could try connecting the 5w bulb to the positive side of the battery and the other side to the output of the amplifier. as you rotate the dizzy the bulb should go on and off. If not, the amplifier could be dead, or there is no supply to it, or its not getting a proper input from the dizzy.

 

Nige

[agent_zed]

Hey,

thanks guys think i was reading the haynes manual wrong as its not worded that well. So i took the dizzy out and cleaned it up a little and put it in a warm place to make sure there was no water in it. Tested it and it returned the correct resistance as per the book. Checked the continuity of the 3 cables coming from the dizzy and they were all fine to the first connection.

 

tested the continuity from the inner connections of the dizzy to the plug on the ign module and that was fine also

 

Tested the + off the coil and have 12v

 

Span the engine with a single sparkplug lead from the coil. no spark

Removed the coil and put a bulb in its place and span the engine. No flashing bulb. So assuming i have read the manual correctly now... If the bulb is not flashing the ignition module or the dizzy is not turning the power on and off to setup the charge in the coil.

 

Since the dizzy is reading the correct ohms and the cables to the module are sound i am thinking now that it could be the ignition module/amplifier.

 

does this seem logical?

 

Mark - this should be similar process for the xflow i would think. Any luck so far?

[sj-bradley]

Try just connecting the spark plug to the coil and ground the coil yourself with some 5 amp wire briefly on / off and see if you can make it spark yourself.

 

To ensure you don't get any back volts from the coil, put your other hand in your pocket. If you can't get any sparks, then either the plug lead, plug or coil is dead.

 

Coil primary should be about 1 or 2 ohms and the secondary should be near 10 or 20,000 ohm (10k - 20k)

 

There may be a common connection between the coils. (Zetec uses a wasted spark so there isn't one in that coil pack)

 

Simon.

[agent_zed]

coil should be fine as i bought a new one last week as i thought that might be the problem. First coil was reading fine but figured it was a cheap part to replace to start with.

 

thanks

[Peter Bell]

Think you will find the flashing light works with a points distributor but not sure if it would work with a hall effect one!

[agent_zed]

think it should as the signal is amplified by the module which then switches the LT negative same as usual. The book describes the bulb method for the electronic dizzys.

 

thanks for the thought though, i'll double check.

[Guest mark little]

Alright all,

I need to go back to basics, when the starter motor turns the engine over what creates the current to the coil, I'm only asking because I fixed the dash back properly after fitting the Speedo drive and wondered if I caught one of the wires, does the coil live come from the ignition? The ignition is accuspark with the ballast coil, the small ballast box has 2 terminals one top and one at the bottom, the top terminal goes to the positive terminal on the coil, the bottom terminal is not connected, is this correct. Just need to get my head around a few of the basics, wiring has never been one of my strong points.

 

Cheers Mark

[Guest Dtr36]

my limited knowledge on my efi pinto is ignition switch provides 12v+ to positive side of coil,12v+ to dizzy there also a negative to dizzy and a twin core cable from dizzy to ecu which switches ecu negative feed to negative side of coil on and off as dizzy rotates

[sj-bradley]

If you have a ballast coil, then the real coil voltage is a 6 volt coil.

 

The ballast is there for cold starting. It is switched out temporarily to put 12 volts (actually more like 10 when cold starting) across the 6 volt coil in order to get a brighter spark for the cold start.

 

Then the ballast goes back in circuit when running so as not to burn out the coil.

 

If you are not getting a spark, I would also check the ballast to see if that works too.

 

You should be able to replace both ballast and coil with a 12 volt version. Don't just replace the coil with a 12 volt one without also removing the ballast as you will get a weak - or non - spark.

 

Simon.

[agent_zed]

Hi Mark,

i certainly don't understand the physics behind it but in its most basic form when a low voltage current is supplied to the coil a larger current is setup in the HT windings. When the LT is switched off the magnetic field collapses and the HT current ramps up and is forced to discharge (hopefully via your spark plugs).

 

Basically the distributor switches the LT wiring on and off at the right time to get the coil to produce the spark. The points dizzy i assume physically switches the negative wire to the coil (might be wrong). On the electronic dizzys there is a pickup which fires a signal to the ignition module/amplifier which then uses that signal to turn the negative on and off electronically.

 

so in theory it must be either the signal or points in the dizzy, ignition amplifier (if you have one) or coil if you are getting no spark at the coil.

 

Hopefully thats somewhere near right as thats what i understand from the reading i've been doing so far.

 

Do you have a haynes manual? i can scan the ignition part if you want. I have the sierra and i think the mk1 fiesta which will be xflow.

 

hth

[sj-bradley]

Yes, you can mechanically test the coil for a spark if you wipe a contact over the LT side of the coil (Effectively make your own switch to switch the coil on/off) and see if a spark appears at the plugs.

 

Points version of distributor does the same thing. The electronic version relies on switching transistors to do the same job.

 

So, if you can mechanically make a spark with a wire, this means either the dizzy side or the internal transistors on the amplifier are dead. (It could be something else with electronics - maybe the input side etc - depends on how complex it is.)

 

Coils and plugs are simple devices. They either work - or they don't (Btw - spark plug gap ok?)

 

Simon.