96 Z 71 burning up ignition coils. Help!

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TJinTexas

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I have a 96 K1500 with the 5.7. I had to replace the fuel pump two weeks ago and the truck ran fine afterwards for a week, then it wouldn't start again. I looked at riter and cap, both had carbon so I replaced them, still wouldn't start (I also replaced plugs and wires). I tested the ignition coil, it showed the secondary coil was bad so I replaced it and it started and ran for a few minutes. I killed it, put air filter assembly all back together and then it wouldn't start again, no fire. I tested coil again, primary check was ok, but the secondary check shows the secondary coil is burnt out again!

Coils aren't cheap and I don't want to keep burning them up, so where do I need to look from here? Any help is greatly appreciated!
 

Dubs

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From what I see in the diagram and what you're telling me it sounds like the module is bad. make sure you don't have a short across the coil from a loose wire. Do you have an aftermarket tach?
 

Schurkey

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How much resistance in the plug wires including the coil-to-distributor wire?

How wide is the spark plug gap?

What are your actual readings when testing the coil?
 

Ken K

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You indicated the primary test ok. Is it around 1.2 ohms or less? While it is true that B+ is supplied to the coil's primary and the ground is turned on by the ignition modules circuit. It sparks when shut off thru mutual induction into the secondary side of the coil. They are insulated apart from each other and while B+ is available while the engine is running, it remains turned on to create a magnetic field. There would be no reason for the secondary to open unless an internal insulation issue. Some coils (Denso) have a diode that will not allow ohms testing from the spark plug end to the ground side, either coil frame to ground when bolted down or thru a wire in the connector. I was taught to use the GM spark tester ST-125 (S=spark, T=tester, 1- version 1, 25= 25k air gap) With coil grounded and plugged in, the tester is plug into the spark plug wire led. Spark or no spark. This test remains the same for coil over, coil near on new products. With mutual induction, even with a bad wire or plug, there is no reasonable answer for burning out the secondary side of the coil. Key on, engine off, using a digital multi-meter (DMM) test for ground from block, battery using ohms. Reading should be 0.400 ohms or less. Clean grounds at battery, engine, frame and ECM G100 on the engine from the harness. B+ should be battery available depending on running or not, but the same as system voltage. Re-check how you are testing this coil and try moving a known good coil to that location. I am not familiar with these engines as i worked at the Buick dealer when these where in service, but if you have multiple coils, move them around. Since the secondary produces very high voltage with very little amperage (>0.005 amps), only internal insulation can cause the wire wound in the secondary could short out and go open. Best of luck, let us know what you find and photos would be nice also.
 
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