Ignition Coil - Need Opinions Pls.

[Off_Timing]

Guys,

Basically, I want to know if I should replace the ignition coil pack.

We have a 2000 Windstar, 3.8L V6 with 131,000 km.

The spark plugs were changed with Ford OEM ones about 10,000 km ago.

Wires and ignition coil are still original.

We have an intermittent misfire on number 5 and 6 cylinder. I hooked up my timing light to each wire and watched the strobe.

CEL is not on. My scanner shows no codes. It's not stalling. It doesn't feel like it's going to stall. You have to feel for the misfire to know it's there.

I cleaned the MAF a week ago.

Tonight, I pulled the wiring harness off the ignition coil pack. The readings between B(+) and the other three connectors were 1.3 ohms, 1.8 ohms, and 1.8 ohms. Haynes says reading should be between 0.3 and 1.0 ohms.

Between the coil tower pairs, I was getting about 13.6 K ohms. Haynes says reading should be between 6.5 k ohms and 11.5 K ohms.

I didn't have time to swap any wires (it's late and getting dark).

What do you guys think. Is the coil bad?

Thanks.

[olopezm]

I would just replace it.

As you must already know from your manual cylinders 5 and 6 aren't in the same winding and since the values aren't within specs...

A friend taught me that clogged EGR ports can also cause misfiring.

Oscar.

[spugeddy]

Could also be a bad wire.... I had a slight charred spark plug wire that was one of the fronts, it must have been making contact with something hot and melted away some of the insulation causiing arcing I am sure....at least visually inspect them (the rear ones are challenging) If you are going to replace the coil, I would also replace the plug wires while you were at it. Did you see any cracks (even hairline) on any of the coil packs towers.....

I am on my THIRD coil pack (155,000 miles)

[suburbanstevie]

Wow, just two weeks ago I had a misfire in #2. I crawled under the car to check the wire on the plug, and the wire sorta crumbled in my hand (135 Kmiles). So figured I needed to change the wires and plugs. Did that and STILL had a misfire. so went ahead and checked the coil witht he ohm meter, and sure enough one of the coils was short.

Could this be your problem? you say the coil checks out OK. But I would still go ahead and change the coil, and seriously think about checking/changing the wires. changing the wires is a somewhat easy task if you remove the cowling. Work slow, (so you don't break any of the little plastic holders). the manuals say to change one wire at a time, but I find it best to carefully diagram the wires (what goes were), and remove them all as two "assemblies" with the clips attached. then you can remake the assemblies and put the clips onto the wires before you put them back onto the engine.

[kafkacell]

Full injectors clogged are also a very common cause of misfire in all Windstar. Cleaned mine 2 months ago and misfire just disappeared. Engine runs way better now. In your case coil seems to be failing but injectors tend to get clogged and needs to be serviced maybe once in a year.

[Off_Timing]

Last night I removed the ignition coil. No carbon tracking. No cracks, hairline or otherwise.

I ran the engine for about a minute before I removed the ignition coil. It felt fairly hot. Anyone know if that's normal?

I was going to swap spark plug wires to see if the misfire follows, but when I hooked up my timing light, 3, 4, and 5 were all missing intermittently.

Physically, there's nothing wrong with the coil. But the high resistance reading (out of spec) I think is the reason for the misfires. Is the high resistance reading on the coil enough of a reason to replace it? They're $180 + 13% tax where I live.

Thanks.

[olopezm]

AFAIK even a slight variation in resistance can cause problem either with coils or wires (I bought a new set of wires a year ago and were slightly higher than normal in resistance, the engine ran so badly that I had to return them and bought a different set).

One more thing is to check continuity between the primary and secondary coils. There should be NO continuity.

Oscar.

[tomj76]

I wouldn't worry about the resistance of the windings, so long as it's not an open circuit (i.e. > 1 Mohm) or a a short circuit (i.e. <10 ohm).

As far as the resistance of the primary windings (low resistance side), it is difficult to take accurate resistance measurements with a DVOM when the value is < 1 ohm. The contact resistance between the probes and the device and the resistance of the probe leads introduce errors. As long as the resistance is not extrememly high (> 10 ohm), I count it as good.

Before replacing the pack, make sure your EGR ports are clear and open, make sure the EGR tube and the signal tubes are not clogged. Make sure your air filter is clear, and that your MAF sensor is clean.

These are all realtively cheap things to check, although the EGR ports take a bit of work to get at.

Without some evidence that it's clearly a problem with the coil pack, I'd change the wires first, because the rubber can only stand up to the high temperatures for so long before breaking down.

As far as the coil pack getting hot.... it will get warm. Electrical power is dissipated in the pack which generates the heat. If it's too hot to touch then it's showing signs that there is an electrical problem. However, it might not be the coil pack at fault. For example, stray sparks can increase electrical current, and cause excess heating in the pack.

[Off_Timing]

Ok, so here's the deal. Boy, do I feel stupid. I'm posting this cause I think there's a lesson to be learned here.

I was using my timing light to check engine misfire. Figuring that inconsistent strobes means misfires.

I bought OEM spark plugs (I start with the cheapest solution first) and changed number 4 spark plug. I ran the engine (sounds smooth) and hooked up my timing light....but no strobe! I thought I really messed up and number 4 was not firing at all. Long story short, the problem ended up being a defective inductive pickup on my timing light. As soon as I used a different inductive pickup unit, my timing light strobe was (pretty much) smooth and consistent.

So now I know, make sure the tools I use are working correctly. Glad I didn't spend almost $200 on a new ignition coil pack.

.....maybe I should buy a scan tool....hmmmm

[kafkacell]

I bought an OBDII USB cable and I use my laptop (OBD software) to scan codes and do real time data. This way I diagnosed a misfire on spark plug number 5. Cleaned injectors and cleaned all spark plugs. No more misfire since then.

regards