Contour Enthusiasts Group Archives Forums General Troubleshooting Is the dealership wrong???

EEC-IV, I believe, had the capability of doing a power balance test during the KOER test. Not sure if OBD-II (EEC-V) has this capability.

In any event, a cylinder power balance test involves shorting the secondary ignition to ground, not primary. This does not involve providing an open in the secondary circuit (e.g., pulling off a spark plug wire to disable a cylinder). You are in essence allowing spark to go directly from the coil tower to ground instead of allowing the spark to jump across the spark plug gap to ground. This is no way damages the coil, ignition drivers (transisters), computer, etc.

Damage could be caused, however, if a person were to pull a spark wire from the plug to disable a cylinder since the spark will find its own path to ground, possibly through the coil and or/drivers.

As far as the test not being applicable to waste-spark ignition systems, that is simply not true. The secondary circuit is never opened during the test. The spark only bypasses the spark plug gap on the cylinder being tested, thus not allowing power to be produced on that particular cylinder only. The companion cylinder spark plug fires normally on both the exhaust and power strokes.

Sorry about the long post, but this is an extremely useful and powerful diagnostic tool that has many misconceptions.

The CBT does not affect the spark side of the system.

It works by sequentially shutting off injectors to see what the effect of a known cylinder drop-out has on the overall performance of the engine while it is under test.

This makes the whole discussion about shorting out the ignition moot.

Getting back to the original problem, a #6 injector is unlikely to cause a P0302 misfire code.

I'd vote against the dealership's diagnosis.

Steve

Rod, this is a friendly debate. I'm in no way taking this to be a flame or argument. I just hope we're not hijacking this thread, but I think the original poster is just going to take his car to the dealer anyway . We may have to take this to PM if the mods think this is too off topic.

Well, to get back to things, a cylinder balance test does not tell you why a cylinder isn't producing power, only to identify which ones. Shorting the secondary spark provides a convenient method to disable the other working cylinders, thus making the one that isn't producing power stand out (due to no RPM drop when disabled).

Once you know which ones, then you will have to use other diagnostic techniques for those particular cylinders such as scope testing the secondary ignition (or primary), compression testing, and fuel injector testing. The tests you perform after cylinder balance pinpoint the reason for the misfire. I hope that answers your question about the possibility of masking a bad injector, if I understood correctly (or were you talking about the companion cylinder?).

I don't know know enough about electronics to agree or disagree with you about the effect of the spark wire's resistivity on PCM performance or electrical performance. I'm aware of the electromagnetic interference caused by low resistance wires on radio reception, however. If you can recommend me something to look at that would be great.

I disagree with you that the spark current will travel to ground when bypassing the 10kohm spark wire path with a 2 ohm ground wire. The path of the secondary spark on a waste-spark system is from one coil tower, spark plug wire to one cylinder, spark plug on same cylinder, cylinder head (block), spark plug on companion cylinder, spark plug wire on companion cylinder, and finally back to the other coil tower on same secondary winding. It's important to note that the same spark that was used to fire the first plug is used to fire the companion cylinder plug (on exhaust stroke). I have text book info to back this up in case you wanted some page scans.

With your reasoning, why wouldn't the spark go directly to ground after firing the first plug instead of jumping across the air gap of the companion cylinder plug to get to the other coil tower? It seems to me that it would be alot more difficult for the spark to jump a 0.030" air gap in the companion cylinder than it would to just go directly to ground after firing the first cylinder.

It's counterintuitive, but that's how the system works. So I don't see how shorting from one tower to the block (bypassing the spark plug and wire) will not fire the companion cylinder's plug. The path from one coil tower to the block is left intact while the companion cylinder's plug and wire is left unchanged. I can send you some scans from my engine performance book if you need more convincing.

And as far as plug wire resistance limiting surge current, you have me on that one. I really don't know much about transformers to say, or really AC electrical analysis for that matter. I'm just a stupid ME.

I don't know if I convinced you, but I know one thing for sure. I'm pooped, that was the longest post I've ever written.

Tony,

Since it was stated from the original post that it went to the dealership with P0302, it has to be assumed that that is what the dealership was supposed to diagnose. If there are other pertinent details, they were not revealed for consideration.

You're giving the dealership way too much credit if you think they hooked up a piece of "highly sophisticated machinery" except perhaps to check the credit line of the customer. Their NGS scanner is no more capable than is Alex's software and a laptop.


Steve

I disagree.

Alex's equipment is among the better ones, but to say that it is better than the WDS or NGS is pure ignorance.

There just isn't enough information here to make a judgement that the dealership screwed up. I have no idea whet they found when the scanned the system. Diagnoses is a lot more than just reading codes.