Fist off, the term "coil packs" is generally misused when referring to VW applications. A true coil pack contains the coils for all cylinders in one block, or pack (who would have thought?). When referring to the commonly discussed VW-coil-pack-failure issue the correct terminology should be coil-on-plug ignition as each spark plug has its own coil, located on the top of the plug. For various reasons people have taken to referring to this type of ignition system as a "coil pack" system. I am not trying to change the naming convention, just trying to make you aware of it.
Engines that use a coil pack
12v VR6 (pre 2002.5)
Engines that use individual coils (coil-on-plug)
24 VR6 (post 2002.5)
Issues with coils and coil packs
The problem here is that both systems are failure prone (not in general, it just seems to affect VW's choice of components). The issues are outlined below.
The issue with VR6 coil packs actually predates the issues with coil-on-plug systems as it started with the MKIII VR6s. The problem comes when the actually casing of the coil pack cracks. Whether from heat, vibration, or something else the cause is not really known, but they will crack. Coil packs generate high voltages, when the coil are exposed (by cracks in the casing), the spark can actually jump to either ground, or another plug wire. This causes engine misfires.
As mentioned above engine misfires, a flashing check engine light, reduced power and bucking are all symptoms of a cracked pack. The behavior is usually exaggerated in wet or foggy conditions as the moisture in the air provides an easier path for the spark to jump.
An easy way to check if your coil is causing your check engine light is to fill a spray bottle with water, start your car somewhere dark (or at night), and spray water onto the coil pack (a black brick like object on the drivers side of the engine (the spark plug wires end on the pack)). If you see sparks, your pack is cracked.
-Is VW aware?
Yes, as noted earlier this issues goes back to the transition of VR6's from distributors to coil packs. HOWEVER VW has never made any official recall of these coil packs, 12v VR6 engines are not included in the recall that went out in 2003 for 1.8t's and 24v Vr6's.
-Fixing the problem
One solution is to buy a new coil pack, they are expensive however. Many of our vendors sell 12v VR6 coilpacks. Another solution is to fix it yourself. This involves filling the cracks (basically coating the pack) with a heat resistant epoxy product. The process is easy, cheap ( under 5 bucks for the epoxy), and it works. It is often referred to buy the name of the product most commonly used, "JB Weld". Three threads that can help you with the process (which anyone can do, it is not difficult)-
a 12v VR6 coilpack
24v VR6 and all 1.8t's
VW has had serious problems with its individual (coil-on-plug) ignitions. For whatever reason, the actual coils (the little boxes on top of your spark plugs), died, and died frequently. This causes loss of power, misfires, crappy throttle response, etc.
Check engine lights, power loss, complete engine shutdown, misfires, basically you should check your coilpacks (if they have not been replaced) anytime you have engine problems.
A scan of the engine codes by the dealer, a friend, or someplace that does it for free can give you insight into the problem. Anything relating to misfires or the ignition system can probably be attributed to the coils. Many times the car will not be able to be driven at all, in this case your best bet is to just have it towed to the dealer. Users in the 1.8t forum and the 24v Vr6 forum are particularly adept at diagnosing coil pack related problems.
-Is VW aware?
Yes they are, and they have issued a recall. At this point in time the earlier supply issues are gone, and your dealer should have plenty of the revised coils in stock. It seems that the newer cars (late 2003's and later) have received the new packs during manufacture, and therefore are not affected (although that is not a rule). Contact your dealer if you think you have coil pack problems. In addition, at this point most dealers will replace all the packs if one goes out and they are an earlier revision.
-Fixing the problem
The coils available now (J and L revisions) seem to have dealt with the problems. Once again contact your dealer.
This thread http://forums.vwvortex.com/zerothread?id=575535, is an account (some 50 pages long) of the entire saga chronicled on the Vortex.
2.0's use two coils in what is called a wasted-spark ignition system. The coil fires two cylinders at once, but since only one of the cylinders is on the compression stroke, the other spark is "wasted". Coil pack problems on 2.0s are extremely rare as they share no components with either of the above two systems.
Diesels are compression-ignition engines, no spark plugs, no ignition system. (lucky you!)
Modified by rs4-380 at 8:08 AM 1-12-2005