StagHunter

Recently my car started missing and showed a code 0303 - misfire detected #3 cylinder. The plugs are 10,000 miles old, the wires maybe 30,000. I didn't see any arcing at night. Hooking a timing light to #3 wire showed the misfire. I'm thinking it's the coil, which is original, but before I pop for a $100 part I'd like to test it. Car is a 94 3.8 V6 BTW.

Chilton's manual says the primary resistance, measured between the B and coil terminals on the plug should be .3-1 ohms, which it is. Secondary resistance, measured between the spark plug towers and coil terminals on the plug should be 6500-11500 ohms. Mine are all open circuit, much higher than spec. So the coil must be bad, right?

My question is should there be any conductance between the primary and secondary windings of the coil? I wouldn't think so and it seems curious that all three coils in this module are bad. Is Chilton wrong or should I just stop fretting and order the part?

usermst9673

just an fyi you can get those coils for about 70 bucks at an autozone.

StagHunter

Thanks for the tip. The local places I looked into (Napa, Advance) were all considerably more.

Here's the deal with the coil. Chilton manual says to measure secondary resistance between the primary coil terminals on the power connector and the spark plug towers. Quote: "Measure...the resitance between each corresponding coil terminal and the spark plug wire towers on the ignition coil." But that makes no sense. There should be no conduction between the primary and secondary windings. It should be open circuit, and that's what I see.

If I measure between the two plug wire towers at the ends of each secondary coil, I get about 13.7K Ohm in each. Still above the range (6.5-11.5K), but at least I get a measurement that makes sense.

Is the Chilton book wrong, or am I still not getting this?

usermst9673

Well heres what alldata said looked it up while i was at work. Im not for sure if i really understand what the chiltons manual asks ive never been a fan of em for much. Btw how many miles are on your car?

Ford does not provide standalone testing or resistance specifications for this component, the only test provided by Ford for the Coil Pack is a pinpoint test procedure. For diagnosis and testing of the ignition coil
Ignition Coil
The ignition coil, which is mounted on the upper intake manifold, can be described as a coil pack containing three separate coil units. Each coil unit is individually controlled by the Powertrain Control Module (PCM) through separate wire leads. Each coil unit activates two spark plugs wired in a series by the spark plug wires.[*]One spark plug activates on the compression stroke and uses the majority of the ignition coil's stored energy.[*]The other spark plug activates on the exhaust stroke and uses very little of the ignition coil's stored energy.[*]Because the pairs of spark plugs are connected in a series, one spark will travel from ground to the electrode while the other spark will travel from the electrode to ground.[/ul]The spark plug:[*]changes the high voltage pulse into a spark which ignites the fuel and air mixture.[*]originally equipped on the vehicle has a platinum-enhanced active electrode for long life.[/ul]The Crankshaft Position (CKP) sensor:

NOTE: Initial engine ignition timing is set at 10 degrees ±2 degrees Before Top Dead Center (BTDC) and is not adjustable.
[*]is a variable reluctance sensor triggered by a 36-minus-1 tooth trigger pulse wheel located on the crankshaft inside the engine front cover.[/ul]The sine wave type signal generated from the crankshaft position sensor provides two types of information:[*]position of the crankshaft in 10 degree increments[*]the crankshaft speed (rpm)[/ul]The Powertrain Control Module (PCM) uses this information to determine ignition coil turn ON and turn OFF times and misfire detection.

StagHunter

When the factory service manual cost hundreds of dollars (when the car was new), the Chiltons was pretty much the only game in town. I have since scored a factory service manual from eBay, but the test procedures are in the Powertain and Emissions manual, which I don't have, and isn't readily available. I may head back to eBay for that one, too. FWIW, I find the Ford manual practically unreadable, and usually end up consulting the Chiltons book first. Maybe I should pick up a Hayne's manual as well.

My car has 119,000 miles on it.

That sounds pretty familiar. I'm sure I've read that either in the Ford manual or the Chiltons, or both. Bottom line is my new coil will be here tomorrow morning and we'll see if that solves the problem. I ended up ordering it from Rock Auto. The Autozone lead was a dud. It seems parts are priced differently depending on where you live. Here in Jersey, a V6 Mustang coil costs $76 as opposed to, say, $56 for that same coil in KY. Go figure...

usermst9673

wow thats stupid autozone does that! oh well. Did the new coil work?

cuda2000

I know this thread is old, but I need an answer on this....
When testing the coil pack on 3.8 v6 mustang, according to haynes and chilton manuals, and autozone (which gets its info from there I'm sure) it says if the secondary resistance is not between 6k and 11k ohms (across pairs of wire connectors) then replace the coil pack.
The one that was in my car read 12.9k on one pair and 12.4k on the two, so I got a replacement and tested it at the auto parts store and it read 12.4k on all three pairs.
Both coils I tested got .8 ohms on the primary side across all 3 terminals.
This is in line with the person who started this thread. So has anyone tested theirs and gotten any less than 12.4k?

I bought the replacement and didn't see a difference (idle is not smooth) so must be a different problem for me, but I'd still like an answer.