Intermittent miss/stumble 02 Windstar

I have an intermittent miss/stumble on my '02 Winstar. It is not regular enough to be a constant miss on a given cylinder. Just that at idle it I experience an occasional stumble a second or two apart, and sometimes the same thing, at about the same interval while driving. It gets worse in wet weather. I have already done the isolater bolts, and recently replaced the plugs (replaced with OEM Motorcraft).

In reviewing former posts, I see several possible causes (coil, EGR, plug wires, etc.)

I was considering trying wiswind's EGR isolation test, but have two concerns. One is the comment that the EGR doesn't operate at idle. If that's the case, it would seem that the fact that I experience this problem at idle would rule the EGR out. Am I correct in this thought? The other is that I pulled the cowl, but couldn't seem to get at the EGR valve wihtout pulling the upper intake anyway. Did I miss something?

Just wondering whether where y'all suggest I should start in trying to diagnose this, because I don't want to just throw parts at it (partly because I am a frugal Scot, partly to keep unnecessary materials out of the landfill).

I'm thinking that I should at least start with new plug wires. Not sure that testing the coil will help, since it is an intermittent problem.

All suggestions are welcome.

Welcome to the forum!

First of all, the EGR valve rarely fails on these vehicles, so stay away from it! It's a expensive component. It is more probable for the DPFE sensor (part of the EGR system) to go bad and cause some misfiring problem but, as you said, only during cruise when the system is active.

I would remove the coil pack and take a look at the rear of it. It is a common problem and tends to crack at the epoxy insulation causing the spark to arc to ground. It is always more noticeable during wet days because of moisture in the air. You can test for resistance with an ohmmeter and pass the test but those small cracks will still give you problems.

Bottom line, if you see even smal cracks at the back of the coil pack, replace it.

Oscar.

Thank you, Olopezm. I'll pull the coil and give it a close look. I replaced the plugs over the week-end (I'd put in a set that weren't double platinum and learned from reading here that that is a no-no). The miss at idle and light acceleration is gone, but I had to punch it this morning, and she bucked a bit, indicating that the coil might be bad after all. If I don't see anything obvious on the coil, would it make sense to replace the wires (they are original and the van has 184k miles).

Hmm...

Those wires are old, I don't know what a regular replacement interval would be but 184k on the original wires is surely too much. From experience I know most people change them at 100k miles.

I know you can measure resistance across each wire to test it, don't know the exact resistance per foot for windstars, maybe somebody else can post it. But since they are original and knowing that wasted spark ignition systems (like our windstars) tend to wear the wires faster, I would replace them first and inspect the coil pack while at it. If the coil pack shows no obvious signs of damage then just reinstall it and test drive your windstar.

I hope that's all it needs.

Oscar.

Thank you, Oscar. After reading other threads, I was thinking that replacement would be a good idea, and might as well, since the cowl is going to be off anyway. (I'm getting really good at that!)

I know you can measure resistance across each wire to test it, don't know the exact resistance per foot for windstars, maybe somebody else can post it. But since they are original and knowing that wasted spark ignition systems (like our windstars) tend to wear the wires faster, I would replace them first and inspect the coil pack while at it. If the coil pack shows no obvious signs of damage then just reinstall it and test drive your windstar.

I hope that's all it needs.

Oscar.

The standard wire resistance should be in the vicinity of 6k to 7k ohms per 12 inches (30cm).

As for coil packs, absence of visible damage and cursory resistance testing does not always mean they are good. Insidious isolator fault will cause misfire and is invisible. It can be detected however by performing a resistance test between primaries and secondaries on each bank (one probe placed on the tower contact and the other on the corresponding primary pin in the coil power connector). This should be a closed circuit, any resistance there indicates isolator fault and the pack must be replaced.

The standard wire resistance should be in the vicinity of 6k to 7k ohms per 12 inches (30cm).

As for coil packs, absence of visible damage and cursory resistance testing does not always mean they are good. Insidious isolator fault will cause misfire and is invisible. It can be detected however by performing a resistance test between primaries and secondaries on each bank (one probe placed on the tower contact and the other on the corresponding primary pin in the coil power connector). This should be a closed circuit, any resistance there indicates isolator fault and the pack must be replaced.

I don't know if I'm not following here, do you mean resistance between the big lugs and the connector blades? If that's the case (I might be wrong) then what you said it's incorrect; primary resistance should be measured between all 4 blades (3 coils and one common); and secondary resistance should be measured between adjacent towers.

Since the primary coil induces voltage to the secondary, measuring resistance between primary and secondary (as you mentioned) should give an OPEN circuit or infinite resistance; any other value for resistance or a shorted circuit (0 resistance) would indicate the coils (primary and secondary) are shorted and needs to be replaced.

Oscar.

I don't know if I'm not following here, do you mean resistance between the big lugs and the connector blades? If that's the case (I might be wrong) then what you said it's incorrect; primary resistance should be measured between all 4 blades (3 coils and one common); and secondary resistance should be measured between adjacent towers.

Yes, and primary resistance should be 1 ohm for each.

Since the primary coil induces voltage to the secondary, measuring resistance between primary and secondary (as you mentioned) should give an OPEN circuit or infinite resistance; any other value for resistance or a shorted circuit (0 resistance) would indicate the coils (primary and secondary) are shorted and needs to be replaced.

Oscar.^

You're right, I did not state it correctly. What I meant to say was there should be no continuity between primaries and secondaries when no load is present.

In all honesty.....if I were going to do the work of removing the coil pack.....I would replace it.
It seems to come up as a failure on the 1999 and newer windstars for some reason.
It can have a crack that you will miss in a visual inspection.
Use care to avoid plugging in the spark plug wires in the wrong places.....very easy to cross them up!.

If the spark plug wires are original, they may be due for replacement.
I get nervous about handling of old spark plug wires as they can become brittle with age.
The less flexing, the better.
I try to only have 1 plug disconnected at a time to avoid crossing them up.
If you replace the wires, use care in the placement of them to avoid contact with sharp/hot surfaces.

In all honesty.....if I were going to do the work of removing the coil pack.....I would replace it.
It seems to come up as a failure on the 1999 and newer windstars for some reason.

The tests are usually performed on-vehicle as part of a misfiring troubleshooting sequence and serve to either confirm or eliminate the coil pack as the source of the problem. It can help avoid needlessly replacing the pack.

Failure due to physical damage is more common on '01 to '03 models which have the plastic-body pack. The '99 and '00 models have the same EDIS-6 unit as first-generation models.

Use care to avoid plugging in the spark plug wires in the wrong places.....very easy to cross them up!.

Indeed, especially considering Ford's odd 4-6-5 sequencing on the front cylinders even though the rear ones are 1-2-3

.... the comment that the EGR doesn't operate at idle.......

This comment (I hope I didn't make it!), is incorrect.

The EGR SHOULDN'T operate at idle.