Weak spark from end of HT leads

[cherrybeard]

Hi, so I have a slight misfire at idle and a bit down on power during low revs and high throttle.

Pulling HT leads one by one:

1 and 3 Quiet clicking sound and no visible sparks

2 and 4 Louder clicking and bright visible sparks arcing to cam cover

Noticed that the HT lead ends on the coil pack had 2 and 3 the wrong way round (probably been like this for a while) and swapped them round the right way.

Now 1 and 2 have weak spark and 3 and 4 have the stronger spark which easily jumps to earth. Not sure what this means is wrong with the coil pack but have ordered a new one (£40 Unimotor branded).

 

Primary coil resistance - 0.9ohm

Secondary coils (1&4, 2&3) - 14.4kohm

All leads show resistance increases in line with their length

Battery voltage at centre terminal of loom connector

 

Question is, if the firing order is 1,3,4,2 then how comes there wasn't a major misfire if 2+3 were connected to the coil pack the wrong way round?

[scottybo]

fairly certain escorts run wasted spark, someone will corrct me if im wrong, so that may have allowed you to get away with it for a while

[the_big_man]

Most older fords run the wasted spark system so you can mix them up a bit and they will still run Prob got a bad coil pack me reckons

[cherrybeard]

 Thanks thought it might be the wasted spark but not sure.

 

New coil arrived today and I checked the resistances.

Primary coil measured at 0.9ohm which is exactly the same as the old one but still almost twice the specified value (haynes). Should I be worried about that?

Secondary coils are slightly lower at 13.3kohm

 

Ill go see the car at the garage tomorrow and see what type of sparks the new coil is throwing out. Is the test I was doing (pulling each lead in turn and watching how easily the sparks jump from the end of the lead to the cam cover) ok as a representation of a healthy coil or does it not mean much?

 

cheers

[condor83]

Hi cherrybeard,

    When I tested my coilpack because I thought the engine was having a missfire I got very similar values so I think the coil is good.

    The spark should looks thin and blue, but not thick or blurrish, exactly as a eletric lighter.

 

    Zetec engines uses waste spark system, thats why you must measure the resistance between a pair of coils outputs and not a output and ground. That's because the coil pack are indeed two coils.

 

Regards,

[cherrybeard]

Condor, I spoke to the technical department at Intermotor and they said that the coils should be around 0.6ohm but that 0.9 is fine!! They said that if the resistance falls to below 0.3 or less then that could put strain on the HT system. Not sure whether they were blagging or not.

Anyways, I fitted the new coil and there is a definite improvement (only round the block driving) but the interesting thing was that when I pulled the HT leads off (as in the test above) cylinders 1 and 3 now have good arcing spark but 2 and 4 are sparking but nothing that you can visually see! Why the hell are only 2 HT leads sparking properly? It can't be a major problem since the car drives 'fine', it would just be nice to have some clarification over the issue.

 

Got a long journey this weekend so will see if any problems are still occurring.

[Stu]

You can't test wasted spark setups by looking for spark on the plug. The plug exposed to atmosphere will always appear to have a very weak spark!

[condor83]

Hi cherrybeard,

    Are you connecting the spark plug to ground when you are testing it?, that is maybe why you ain´t seeing the spark.

    When I tested my coilpack I did that because I saw a weak spark or the spark wasn´t comming from the tip.

    Respect that you reading 0.9 ohms at the primary that could be related to the accuracy of the instrument, I don´t know what instrument are you using but usually tester/multimeters ain´t to accurate at very low ohms, some I had when I short circuited them I read something between .2 or .3 so add that to .6 and would read .8 - .9 ohms. Although don´t bother with that, the important readings are for the outputs because when the coil overheat it burns the wires isolating coating and that leads to a low resistance reading.

    However just testing the coil thru its resistance isn´t definitive, you could read acceptable values but once it get hot and/or it's operating at high voltages the real resistance could be much lower, because with a tester you are only testing it with 9V at best.

 

Regards,

[cherrybeard]

The test im doing is whilst engine is running, pulling a ht lead off the plug and holding the bare end of the ht lead in the vicintiy of the plug well opening so no plug attached to the ht lead. Just watching for sparks coming out the end of the insulation and arcing to cam cover, so technically arcing to ground.

 

As for testing resistance, im using £30 multimeter so no idea on accuracy really. I will give it another go whilst the coil is hot.

Also, I am testing the coils with all connections removed I.e. off the car. is this ok?

 

is there a way I could test the coil without soecialist equipment?

Cheers

[cherrybeard]

Well the new coil pack worked wonders.........for about 5 hours into my 8 hour drive. Engine was pulling strong in all gears even at low revs.

Then I out my put down in 5th going up a hill and something went 'click' (metaphorically not audibly) and it diverted straight back into shite mode again and has been like it since.

Ive just got home from the return journey (6 hours of labouring the engine) so will try and do some testing tomorrow but to be quite honest the car is a total shitbag and ive kinda lost interest after almost 6 years of chasing possible dodgy sensors, wiring breaks and random air leaks.