I have an intermittent problem on 3 cylinder, coil pack. Today got the coil pack out and tried testing it with multimeter for resistance. Tried continuity and resistance but none of the number had any sence.
So I'm asking where to probe the coil pack to check for resistance.
Car is punto 1.2 8v, 2001.

Thank you.

The low tension coil is checked across the pins at the plug on top of the coil. Should be about 0,5 Ohm.
The secondary high tension coil resistance is measured between the two ht leads. Should be about 7 k ohm.
What readings are you getting?

Rare (but possible) for a coil pack to go down on one cylinder. What's happening with the spark on no.2 cylinder?

Have you tried swapping the coil packs round?

On LT is reading 0 on HT reads 8,5k ohms, on both packs. Now swapped packs and waiting for rough start to occur and check if the problem "moves" with pack.
Problem is that the car starts rough and after few seconds it settles. But lately it settles after a few re-starts. This rough start occurs about once a month, regardles of weather (cold,hot,humid,dry) or engine temp (cold,hot).

If it's only misfiring on start up, I'd be inclined to discount the coil packs. Leads are more likely.

Can be (but don't be scared) early signs of a head gasket on the way out.

I'd think lead(s) more likely than coil packs, but see how you get on.

Sometimes a misfire on start up can be a head gasket on its way out (early signs, keep an eye on coolant level).

I would agree with Fingers. If a coil pack is dead both cylinders are too. The 8,5k sounds ok.
What range setting are you using to measure the LT side. 0 - 1 or 1 -10 ? Some meters find it difficult to read small resistances. Does the meter have a zero function? It is by far more likely that the HT leads are causing the trouble rather than the packs themselves.
Slight misfire at idle when cold is an early sign of headgasket failure, usually accompanied by steam from the exhaust, falling coolant levels and maybe a slight gurgling water noise from the heater matrix in the first few seconds after starting. If you remove all the plugs and find one or two a different colour to the rest that would also point to headgasket trouble.

Musfire is not related to outside temperature or the car temperature. It just happens every now and then.

Run the motor in the dark and see if you can see sparks leaking out anywhere along the HT leads. Spraying them with WD-40 can help prevent misfiring, temporarily at least, especially if water is getting in at damaged leads.
For the cost of new leads I would be inclined to replace them anyway. They don't last forever - although mine are original and still doing fine.

Test a coil pack thats failed
I've tested 2 for resistance and there fine but both HAD failed

Why?
The coils packs on a multi-meter aren't under any load, so that tiny break / crack / overheated bit isn't causing a huge issue

Now put it underload, that problematic area cant cope and the coil pack doesn't fire

tbh i'd test with what you can see - is there a spark and a good one?
No - its probably time to replace it

ziggy

After a bit of time, got today under the bonnet at removed ht leads and spark plugs. The plugs did 12k miles (written on service note). 2 of them have white deposits and 2 of them are grayish. Made a picture but don't know how to post it... Did resistance test on ht leads 2 of them were 650-ish ohm, 1 was 550-ish and last one was 450-ish, and also saw 3 of them are same brand and fourth is a different one.
What can I test or check further ? Spark plug on HT lead and into coil pack and check for spark strength ?

Thank you in advance.

testing HT's is pointless too unless you get a new reading and check later on in life to see if there is a change

Why? there all different lengths = Different resistances
So no point

as for checking spark - yes you can

get the spark plug out - and fit an old plug to prevent petrol vapour escaping out cylinder

You can then put the spark plug on the rocker cover and move it away slowly to see when it stops sparking

if it can jump about 1inch (3 - 4cm) then its all good tbh

Ziggy

If its badly sparking can the cause be the HT leads ? Fitted new spark plugs and car still misfiring, and changed coil packs around and still if I disconnect the HT leads from bottom pack (one closer to front of the car) the car dies. Are my assumptions good ?

It'll be the leads. Get new ones.

Even if they were the same length (and therefore gave the same resistance) the voltages involved will find the tiniest fault in the casing and jump to earth. If the voltage goes to earth, it can't go to the plug, so either no spark or bad spark.

Hope that new HT leads will cure the problem. Next week going to mechanics to do a compression test if its good changing leads. The mechanich had same punto, changed plugs, leads and coil packs. None cured the problem did a compression test and had bad compression on one cylinder.
Thank you guys for the help.

Changed spark plugs, leads and coil packs and the car is still misfiring. Compression test was good. Did that test if my ECU is bad or coil pack and saw that tester was dimly flickering so I guess the ECU is fine.
Do you guys have any more idea what to check on the bloody car... ?

You've got to define "good".

Do the olde start at night, look for blue flashes, trick (bonnet up, of course ).

If that shows nothing, I'd find out which cylinder is misfiring, and look at that injector.

Misfire should result in EML. Code read may suggest something.

Injectors have the same resistance 13,8 ohm. Is this a definitive test or do I have to test them in a different way ? Hoping to put it on a computer today or tommorow.

ljubo700 said:

Injectors have the same resistance 13,8 ohm. Is this a definitive test or do I have to test them in a different way ? Hoping to put it on a computer today or tommorow.

Click to expand...

well it appears they are all wearing the same

Other possibility is the injector has a blockage, or is just dribbling instead of spraying fuel = a poor bang or little bang = slight miss as its not getting the bang it needs

I'd be popping them out and checking

I'd be cheaky - pop all 4 into bottles - disable the ignition system, and crank the car over to check what its like

Ziggy

Looks like injectors 1 and 4 have gone, tommorow going to buy second hand ones, and change them and report back, hopefully this will solve the damn puzzle.
Thank you guys for the help.