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Discussion Starter #1
Two observations:

1. Why add multiple single-points-of-failure to a design (4, 6, or 8 'coil packs'), where previously there was only 1 single-point-of-failure i.e. the centralized ignition tower? Did they achieve at least an 4/6/8 fold reduction in defects and 4/6/8 fold increase in MTBF? I'd have to work the numbers out, but I'm guessing they'd actually need something like a 30 or 40 fold increase in reliabilty of each to wind up with the same likelihood of failure overall.

2. Coil packs rest directly on the engine block. Gee, I thought heat was the enemy of electronics? At least they didn't put the packs on the turbo exhaust housing?


So, if these are the risks, what are the advantages?
 

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Re: Coil pack design philosophy: pushing the envelope? (RechtsFahren)

This design eliminates another 4, 6, or 8 points of failure, the high tension spark plug wires. It also will provide more voltage to the plugs since there will be no loss through those plug wires.
As for the heat issue, well, that's a good question.

Remember, there are B5s out there that have had no coil pack failures in many miles of driving. This problem was one where a particular vendor supplied the parts that failed early. It happens. Early B5s were built with aluminum tie rod ends that failed. Luckily that was considered dangerous enough to cause an accident through loss of steering, so a recall was done.
 

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Re: Coil pack design philosophy: pushing the envelope? (SteveD)

Does it not also allow for more flexibility in engine performance, by allowing more control over each cylinder's ignition? Or am I making this up?
 

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Re: Coil pack design philosophy: pushing the envelope? (SteveD)

I don't think it's a design issue, more of a QA issue. My 1998 had all of it's original coil packs when I sold it last year with 85,000 miles on it...
 

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Re: Coil pack design philosophy: pushing the envelope? (duandcc)

I'm not heavy into the design specifics of this, but basically having one puts you in a position of a single point of failure, having four or six still allows you to limp... Secondly, it allows for more freedom as the time necessary to build up a charge to fire a plug cylinder goes up by a factor of four (or six..). It's this last item that is the driving factor, ibt. From a cost standpoint, it raises the cost, and is anathema to VWs production parts control pholosophy otherwise, so they wouldn't do it if their weren't some notable performance (power, smog, etc.) benefits.
 

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Discussion Starter #6
Re: Coil pack design philosophy: pushing the envelope? (Green_Hornet)

All good points, everyone! On the limp mode though, that comes at a high price (potentially) if it ruins your cat. Anyone know roughly how long we can limp without ruining the cat i.e. just to pull to the shoulder, just to go a few miles?

That's interesting, I thought it might buy more time to build up a good spark.

What I was surprised to see was that a number of people with the older AEB have had failures, too, just not as many (but it still seems out-of-the-ordinary), and some VR6 people on the 'tex saying packs have not been overly reliable on the VR6 either.
 

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Re: Coil pack design philosophy: pushing the envelope? (RechtsFahren)

There are many benefits to multiple coils. The V6 has multiple coils as well, they're just not a "coil-on-plug" design (so there's even more points of failure - the individual coils and the wires). The problem is not inherent to having multiple coils, it's a design flaw or defect in the parts VW has chosen. My 9 year old / 140k mile Audi has individual coils and they're still original. When it's fixed all will be well. Don't count on engine designers going back to a single coil with emissions always getting stricter.

<BLOCKQUOTE>quote:<HR>Anyone know roughly how long we can limp without ruining the cat<HR></BLOCKQUOTE>

I wouldn't go very far at all. However, if you open the hood and disconnect the injector (it's also computer controlled, has a little plug on the back of it) you should be able to go pretty far. Unfortunately that requires you to spend some time diagnosing which coil has failed.


<![CDATA[There are many benefits to multiple coils. The V6 has multiple coils as well, they're just not a "coil-on-plug" design (so there's even more points of failure - the individual coils and the wires). The problem is not inherent to having multiple coils, it's a design flaw or defect in the parts VW has chosen. My 9 year old / 140k mile Audi has individual coils and they're still original. When it's fixed all will be well. Don't count on engine designers going back to a single coil with emissions always getting stricter.

<BLOCKQUOTE>quote:<HR>Anyone know roughly how long we can limp without ruining the cat<HR></BLOCKQUOTE>

I wouldn't go very far at all. However, if you open the hood and disconnect the injector (it's also computer controlled, has a little plug on the back of it) you should be able to go pretty far. Unfortunately that requires you to spend some time diagnosing which coil has failed.


[Modified by Macabre, 9:58 AM 1/2/2003]
 
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