91 ZR-1 Cutting Out Under Load

[ZR1North]

Originally Posted by ZR1North

What a great thread!

I pursued Greg's tip and purchased the "D555s" noted above, but I am not sure I want to install them now that I have them.

On these new units, the secondary windings are measuring 5.6 to 5.8K which is close to the GM recommended range of 5.6 to 5.7, but the primary windings are measuring 1.7 ohms - GM recommendation is .5 ohms. I am also a little suspecious of the part no on the replacements; it is 10482928 rather than the numbers Greg quoted above. I am thinking - don't think I will use these replacements. Am I being too cautious?

I LIKE JERRY'S REPONSE TO MY QUESTION. I'D BE INTERESTED TO KNOW IF ANYONE ELSE HAS SOME WISDOM TO ADD TO THIS - APPRECIATED!

JERRY'S RESPONSE:

CAVEAT: I'm no expert on the subject but think I understand the principal according to the following tech article.

Transformers/Ignition coils

Transformers step-up (increase), step-down (decrease), or pass-through (same level) AC voltage or pulsed DC voltage. A basic power rule applies to transformers; power-in equals power-out. The unit of measure for Power is the Watt. 1 Watt = 1 Volt x 1 Amp.

A transformer has three main components:

An iron core - The iron core is wrapped with two separate coils of wire. The job of the iron core is to strengthen the magnetic fields of the transformer.

Primary winding - The input side of the transformer. This coil of wire is tightly wrapped around the iron core of the transformer.

Secondary winding - The output side of the transformer. This coil of wire is tightly wrapped around the primary winding of the transformer.
There are three basic types of transformers:

Step-up transformer - The primary coil winding has less windings of wire than the secondary coil does. A 1:2 step-up transformer has half as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 24 V AC will be induced into the secondary winding, however, the output amperage will be cut in half to 6 amps.

Step-down Transformer. - The primary coil winding has more windings of wire than the secondary coil does. A 2:1 step-down transformer has twice as many primary windings as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 6 V AC will be induced into the secondary winding, however, the output amperage will be doubled to 24 amps.

Pass-through transformer - In a 1:1 transformer, the primary coil winding has just as many windings of wire as the secondary coil does. This means that if you apply 12V and 12A to the primary winding, approximately 12 V AC will be induced into the secondary winding, and the output amperage will be 12 amps. The advantage of a 1:1 transformer is that there is not a direct electrical connection between the two coils. If one side of the circuit gets short circuited, the other side will remain isolated.

Examples of transformer use on automobiles:

Ignition coils - An ignition coil is an example of a step-up transformer, the primary coil input voltage is 12-15 V and the secondary output voltage is 20-60 kV. This means for every primary coil winding there are at least 2000 secondary windings. This also means that the output amperage will be at least 2000 times smaller than the input amperage. Secondary ignition voltage is high voltage, but amperage is low.


Quote:
.....the primarly windings are measuring 1.7 ohms vs the .5 ohms specified by GM. The secondary windings seem ok (the new ones are measuring 5.6K to 5.8K which is close to the 5.6-5.7K quoted by GM).

Since only resistance is known and number of windings is unknown, I assume that winding wire size & type is the same, therefore resistance is a function of length of wire in the windings.

I interpret your findings to show that the resistance of the primary windings in the eBay coil is 3.4 times that of the OEM LT5 coil, meaning it has more windings. If the resistance of the primary windings is higher and the secondary windings resistance is the same, that means the voltage output would be lower than the OEM LT5 coil, i.e. coil discharge voltage is not as high as the OEM LT5 coil.

My non-expert opinion, don't use them. The spark is not as hot.

However, I do have my flame suit on![IMG]http://images.ibsrv.net/ibsrv/res/src:forums.*************.com/get/images/smilies/lol.gif[/IMG] END OF JERRY'S TAKE

[scottfab]

Generally I’d have to agree with the functional description of a transformer entered. However, there are a few assumptions that cannot be made. Some matter some don’t. The core of the transformer may not be iron. It’s probably a composite ferrite. That does not matter.
But to assume the diameter of the primary wire is the same as the GM part may be a mistake. Assuming this was done on purpose as a method of increasing reliability it may be that a smaller diameter wire was used. This would make it possible for the manufacturer to use the same number of windings but draw less power. Less power would mean less heat internally. Less heat at the windings could translate to fewer shorts between windings. This is pure speculation on my part but I’d guess the higher primary winding resistance was done on purpose.

Generally using winding resistance is a poor way of judging coil quality. While differential resistance between like type parts is better than nothing a truer measure would be output voltage swing measurements. And what’s more doing this measurement while the coil is at high temperature would be a great test. I am not sure of what the major failure component would be on these coils but I am guessing either internal shorts OR high voltage arching internally. An internal arching problem is not likely to show up on a static resistance measurement.

What I’ve read about the Summit and Accel coils on this thread does not confirm to me that they are bad. If the primary connectors were not pinching the spade end of the car’s connection addequately that is easily fixed my squeezing them together before assembly. Such a failure does not mean the coil cannot produce the needed output voltage. Of key importance on these coils is longevity at the temperatures in the engine valley that the LT5 has.

I’d sure like to get my hands on a coil that fails. Even better, one that reportedly fails on only one side. That is, each coil sparks two cylinders each time if fires. (one is on exhaust stroke the other on compression) On a failure such that only one side fails it should be possible to swap the two plug wires right at the coil and see the failure move to the other cylinder. Yah, that would be a lot of plenum work

[GregCrowe]

Originally Posted by Jeffvette

Another too good to be true? Those are half the cost of AC delco direct from delco.

Yes, I found out this guy up East is misrepresenting these coils as new. They are just take-offs from who knows what. I bought a set from him and promptly sent them back when I found out what he was doing.

The coils I installed on the car were real new GM D555's in GM boxes from O'Reilly Auto Parts.

[A26B]

Originally Posted by scottfab

......But to assume the diameter of the primary wire is the same as the GM part may be a mistake.

You gotta make some assumptions somewhere as a starting point or it's going to turn into a book no one wants to read. I think you even made an assumption