Anyone running the United Motors vented distributor cap?

[454cid]

Have you tested the ignition coil? Failed ignition coils are a common cause of repeat module failures.

I checked the resistance with a VOM and it was in spec. Is there another way to test it? I actually bought a new coil, but didn't install it since the original was in spec for resistance and it's a bit of a pain to replace, as it's riveted onto the bracket.

 

[Schurkey]

Testing coil resistance is the BEGINNING of testing an ignition coil.

If it won't pass a resistance test, the coil is defective. If it DOES pass the resistance test, it may still be defective.

Ideally, you would look at the ignition voltage pattern on an oscilloscope. Most folks don't have access to a 'scope, so the next-best thing is to use a sub-$15 spark tester calibrated for HEI ignitions.

https://www.amazon.com/Performance-...ywords=Spark+Tester+HEI&qid=1618784338&sr=8-7

If the coil can reliably fire the spark-tester, AND passes resistance tests of primary and secondary windings, and windings-to-ground...it's probably good.

When the internal insulation begins to break down inside the coil, an ohmmeter often won't "catch" it--the ohmmeter is testing at very low voltage, but in operation the coil is subject to extremely high voltage. The coil can still work--but it's very hard on the module. As it gets worse, the coil won't have enough power to fire the plugs under heavy acceleration, but it might idle and cruise just fine.

 

[Supercharged111]

Testing coil resistance is the BEGINNING of testing an ignition coil.

If it won't pass a resistance test, the coil is defective. If it DOES pass the resistance test, it may still be defective.

Ideally, you would look at the ignition voltage pattern on an oscilloscope. Most folks don't have access to a 'scope, so the next-best thing is to use a sub-$15 spark tester calibrated for HEI ignitions.

https://www.amazon.com/Performance-...ywords=Spark+Tester+HEI&qid=1618784338&sr=8-7

If the coil can reliably fire the spark-tester, AND passes resistance tests of primary and secondary windings, and windings-to-ground...it's probably good.

When the internal insulation begins to break down inside the coil, an ohmmeter often won't "catch" it--the ohmmeter is testing at very low voltage, but in operation the coil is subject to extremely high voltage. The coil can still work--but it's very hard on the module. As it gets worse, the coil won't have enough power to fire the plugs under heavy acceleration, but it might idle and cruise just fine.

So you hook the coil wire right to that and not a plug wire? My 1500 has a 4000+ RPM misfire that I've failed to diagnose. Coil would be an easy answer, but I have yet to properly test it save for dumping water on it while running which did nothing.

 

[454cid]

If it DOES pass the resistance test, it may still be defective.

That's kinda what I figured you'd say. All I could find online at the time (this is an older thread) was about the resistance tests.

So, like Supercharged asked, I assume I'd connect the spark plug tester to the coil wire going to the cap, then turn the engine over with the fuel pump fuse pulled and watch for a consistent hot spark?

Does the Insulated Boot Puller on the same page as the tester look decent to you? I may go ahead and buy that too.

 

[Schurkey]

Yes, you can connect it directly to the coil wire, when testing the coil. You'd need to assure that the coil wire itself is good.

You'd maybe connect it to the plug end of a plug wire, (each in turn) if you were checking the integrity of the cap and rotor.



Thousands of years ago, I had a high-speed misfire in my '88 K1500. Turned out to be a cracked magnet by the pickup coil. It's not replaceable separately--you'd need a new mainshaft. I have a thread started on this, but it's not finished. The magnet-cracking problem is REALLY COMMON.

https://www.gmt400.com/threads/tbi-hei-small-cap-hei-ignition-problem-areas.52686/




The plug-boot puller isn't showing up for me. I don't usually use one.

 

[454cid]

Yes, you can connect it directly to the coil wire, when testing the coil. You'd need to assure that the coil wire itself is good.

You'd maybe connect it to the plug end of a plug wire, if you were checking the integrity of the cap and rotor.

Testing the coil wire..... is there anything more to that than checking resistance?

My primary interest is the coil....unless maybe an aging cap/rotor could take out the Vortec ICM? When I get to this, I'll likely be swapping out the cap, rotor, wires and plugs any way. Maybe even the whole distributor, If I'm doing my intake manifold gaskets.

 

[Schurkey]

Testing the coil wire..... is there anything more to that than checking resistance?

Coil/plug wires need reasonable resistance, and good insulation.

Assure that the insulation is in good visual condition, not burned, not brittle/crunchy. Then run the engine in the dark, look for glow around the wires (corona effect).

My primary interest is the coil....unless maybe an aging cap/rotor could take out the Vortec ICM? When I get to this, I'll likely be swapping out the cap, rotor, wires and plugs any way. Maybe even the whole distributor, If I'm doing my intake manifold gaskets.

I wouldn't expect a cap/rotor to fry an ignition module.

 

[454cid]

Coil/plug wires need reasonable resistance, and good insulation.

Assure that the insulation is in good visual condition. Then run the engine in the dark, look for glow around the wires (corona effect).

Okay, that's simple enough, thank you very much.

 

[Supercharged111]

Coil/plug wires need reasonable resistance, and good insulation.

Assure that the insulation is in good visual condition, not burned, not brittle/crunchy. Then run the engine in the dark, look for glow around the wires (corona effect).


I wouldn't expect a cap/rotor to fry an ignition module.

I've known to look for arcing in the dark, but glowing is a new one for me.

 

[VIKING_MECHANIC]

Here it is, came Friday. Hope to get it installed after lunch. The little round thing is the vent; in the upside down picture, you can see the hole for it. Hope it works as advertised!

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It looks well made,and has a "heft" to it that the cheap caps don't have.

That looks very familiar. It's very similar to the Davis Unified Ignition I use in my trucks. Right down to the color and material imagine. Possibly made by/in the same factory?

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