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Misfiring - Spark Plug, Injector, or Coil Pack?

10-12-2010, 01:14 AM
Ok, I know there's already info on misfires. Bear with me and hopefully, someone can tell me if I'm going the right direction or if I'm off.

I have a 2000 Windstar with 125,000km. 3.8L V6. The plugs were replaced last summer with Ford oem plugs from the dealer. All other ignition parts are original. Battery was replaced last fall and the voltage reading is good.

I have a misfire at idle. It's not throwing a code. CEL is NOT on. I can feel the misfire.

I detached the EGR top vacuum hose and plugged the hose. It didn't make a difference.

I put my timing light on the three spark plug wire accessible from the front (without removing the cowl). Wires 4 and 6 are ok. The misfire is coming from number 5, I can see the timing light miss the odd time.

Question. Since I found the miss while attached to the plug wire, does that mean I can eliminate :
The spark plug - I'm thinking the plug isn't firing if the coil doesn't send the signal.
The plug wire - same reason, if the coil doesn't send the signal, the wire can't carry it.
The Injector - it doesn't care if the spark plug is firing.

I'm thinking the problem is the coil pack. I didn't get a chance this weekend to pull the coil pack for testing.

Am I correct in my assumptions, or should I go and check the injector, the plug, the wire, then the coil packs?

I traced the wires fro cylinder 4,5,6 going around towards the back of the engine (under the cowl). Can I access the coil pack if I remove the cowl or do I need to get at it from under the van.

Thanks a lot.

10-12-2010, 04:23 AM
The cowl is easy to remove ... don't be afraid of it. You need to remove the cowl to get proper access to the cables and ig pack. With your miles, I would go ahead and ante up for both cables and ig pack.

Don't overtighten those plugs!

10-12-2010, 05:39 PM

Let's take a stab at this.

First, If you've put the timing light on the #5 wire and you can see that it's not firing, it certainly looks like you're in the right direction. You could always swap wires with the cylinder next to it. (JUST TO BE CLEAR HERE.....swap both ends of the wire. Move the bad wire IN ITS ENTIRETY, to a known good plug and retest) You shouldn't worry about the injector, it has no idea about the firing.

The plug wire could be the problem, but I'd suspect a bad coil. I've got a 2000 Windstar w/ 3.8l and an subscription for it Unfortunately, what I'm out of town and don't have ready access to my van and my subscription just lapsed, so what I'm about to tell you is strictly from previous experience on other vans and somewhat off the top of my head.

The coil packs are probably three coils that each have two contacts. So, just for discussion sake, lets say that the coil packs are bunched like this (1,4 & 2,5 & 3,6). As the engine approaches firing time for cylinder 1, it's going to fire both cylinder 1 and 4. It doesn't matter on 4 because of the pistons location in the combustion cycle. The connector coming from the computer to the coil pack is probably a four wire connector. One is going to be 12v constantly. The other three momentarily ground in sequence. As one wire grounds, it will fire it's respective coil packs and then immediately return to a high (non-ground state).

Using what I've discussed, you should have some new troubleshooting to do. You should check the spark plug wire that is on the same coil as your suspected bad one. If it's good, you can do some shadetree mechanic-ing here. Put your known good wire on the other side of the coil pack. (the one you just tested) Leave the known good wire disconnected (you don't want to misfire multiple cylinders at the same time...I'd rather simply misfire one and have the other not fire at all) Your car will run very rough because you are down to 2/3 of your available cylinders, but you should definitely be able to check your timing light to see if you are getting fire to that cylinder.

Bad news for you is that if any single coil goes bad, you'll have to replace the coil in its entirety. If you find out that the coils are good, you'll need to move toward the computer to troubleshoot further.

Now my final disclaimer....everything that I've offered was off the top of my head and from my experience working on a Chrysler van. Perhaps Ford did it differently, but I doubt it. Good luck and let me know how it turns out.


10-12-2010, 08:40 PM
To simplify things, just change the coil pack. In 140,000 miles I changed mine twice already.

10-12-2010, 10:17 PM
To simplify things, just change the coil pack. In 140,000 miles I changed mine twice already.

knock on wood, i've got 172k miles on mine with the original. my suggestion:
start w/ plugs and wires.

10-14-2010, 09:32 PM
To simplify things, just change the coil pack. In 140,000 miles I changed mine twice already.

Why spend money without troubleshooting? What if it's his spark plug wire and he buys an unnecessary $50+ part. What I've suggested shouldn't take more than 20-30 minutes to try. I do think that he's probably got a bad coil, but I don't purchase anything until I'm sure it's bad (or I can't properly test it)


10-15-2010, 01:01 AM
Thanks for the suggestion guys. I have to wait till the weekend, but I'll remove the cowl and check the primary and secondary and secondary resistance first. if they check out, then I'll remove it and check for cracks.

I've run the engine in a dark garage at night, and I didn't see any glow from arcing.....but that's inconclusive.

I'll check the wires, then the plugs after that.

You guys are lucky....I priced the cost of a new ignition coil around here, $158 plus taxes.

Thanks again.

10-15-2010, 01:19 AM
Have you looked at I'm not sure about shipping to Canada and what not, but the MOST expensive one they had (which was Motorcraft) was around $50. Even if you gotta pay a little extra for shipping, it's gotta beat that. has always been extremely cheap on car parts. If you've got a few days to wait, it's worth it. BTW, for everyone else, recently, I've used Amazon quite a bit. They are right in line with Rockauto on most of their stuff and I have a free Prime account (because I had an .edu address) and so they are another very cheap parts source. (And quick....if you have Prime).

Timing, Keep us posted on the progress....btw, how you gonna check the primary/secondary on those coils? It seems to be somewhat useless to me. If you swap the wires, you'll know the culprit. Measuring resistance of coils is not really an exact science. Unless its absolutely open, how are you gonna determine whats good/bad. Just curious.


10-15-2010, 09:02 AM
Mark is right about testing the coil pack leading nowhere ... but I did have a pack that failed once, and there was significant conductivity between the two cable terminals of one coil and ground. Sufficient, but not necessary, for proof of failure ....

10-15-2010, 07:27 PM
I was so focused on checking the resistance, that I forgot about just swapping the plug wires. I'll probably do that first then. Thanks for reminding me.

I was going to check the coil resistance and compare number 5 to number 4 and 6. But like you guys said, swapping the wires will be a better test.

10-15-2010, 07:33 PM
Try rolling the injector, plug, and cop to another pos,
also do a compression check.

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