Ohm's on LT4 Coil ?
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 23,165
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From: San Antonio Texas
Ohm's on LT4 Coil ?
Checking for an intermitten multi misfire on My LT4. Took the coil off to check it out. It has a small plug on one side of the top across from the High Volt out to the Opti Dist. The small plug has 3 pins in it. I measured only .3 OHMS between them all. It didn't matter which two I measured between, the reading was the same .3 ohms. Also measured from the HiVolt to the case and got nothing (open). Measured it then to the 3 pins and it was 5.8K ohms. Again it didn't matter which one, they were all the same 5.8K. I don't know what is normal for one of these. Anybody measure one before
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
I have an 87, and haven't even measured my coil, but your measurements sound about right. The case is not connected to anything. An impedance bridge to measure inductance and Q is a better measurement, but even better is to pulse 12v to the primary with a .05 Mfd to 0.1 Mfd capacitor across the primary. You can use a capacitor from the old points distributor days. When you disconnect the 12v to the primary you should get a fat spark easily 1/2 inch long from the secondary.
Drifting
Joined: Jul 2001
Posts: 1,296
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From: Largo Florida
Checking for an intermitten multi misfire on My LT4. Took the coil off to check it out. It has a small plug on one side of the top across from the High Volt out to the Opti Dist. The small plug has 3 pins in it. I measured only .3 OHMS between them all. It didn't matter which two I measured between, the reading was the same .3 ohms. Also measured from the HiVolt to the case and got nothing (open). Measured it then to the 3 pins and it was 5.8K ohms. Again it didn't matter which one, they were all the same 5.8K. I don't know what is normal for one of these. Anybody measure one before
Safety Car
Joined: Feb 1999
Posts: 3,504
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From: Mexico Beach FL
Unfortunately, jfb is right; checking the resistance doesn't tell the entire story.
If the coil was open, resistance would tell you that.
But, for example, if one winding was shorted, the difference in resistance would be hard to detect.
As jfb said, impedence checking would be much better.
However, some of that equipment can get expensive.
So, for the average person, coil substitution would probably be the easiest way to check.
Tom Piper
If the coil was open, resistance would tell you that.
But, for example, if one winding was shorted, the difference in resistance would be hard to detect.
As jfb said, impedence checking would be much better.
However, some of that equipment can get expensive.
So, for the average person, coil substitution would probably be the easiest way to check.
Tom Piper
Last edited by Tom Piper; Sep 18, 2007 at 08:32 AM.
Thread Starter
Team Owner
Joined: Feb 2006
Posts: 23,165
Likes: 117
From: San Antonio Texas
I'll check out the Ignition Module. Got it off for cleaning & regreasing with fresh heat sink compound. There is an Advance Auto just down the road a couple of miles from me too. It sounds like the coil is probably OK. As nasty, expensive and hard to reach as that Opti is, with my luck, that's probably going to be where the problem is
