4g61t.org

My 90 is running terribly and I traced it down to no spark at cylinder 1 so I swapped in a spare coil pack. Everywhere I checked with my DVOM was the same as the old one but on a whim I still swapped it. The car still runs rough.

I found the diagram for how to test the 91-94 "triangle plug" coils but not the early "square plug". Help please.

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No colors anywhere, I want them painted Black.

Look the post #4 here : http://www.dsmtuners.com/threads/is-thi ... -153113400

Thanks. That's the same thread that was linked when I asked on tuners, which makes me think that it was easier to find than I thought. I did use the search function, maybe not enough though...

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No colors anywhere, I want them painted Black.

I take it you narrowed it down to the PTU? I've never had or heard of a back 1G coil pack. The ignitor things tend to go bad here and there however.

That's the last thing I have to check. They font like heat and this happened to have failed in a 105* day. I'm rolling the dice a bit but oh well.

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No colors anywhere, I want them painted Black.

I would have thought that a power transistor would have failed on two cylinders, as each channel is waste spark and operating every 360 degrees, versus 720 for a single cylinder.

It "should" take down two cylinders if it were bad, assuming the rest of the chain was working correctly. The coil pack could ohm fine when cold, but produce another characteristic when hot ... even an open once quite hot. They do get very hot sitting in the intake valley.

I could be wrong about this.

I have seen pictures of coil packs that were melting and growing liquid plastic out their sides, and I have also seen power transistors that grenaded or had bad terminals and overheated. I had a few green terminals starting on mine, so I repinned it with some of an extra wiring harness. Not perfect, but clicked in and was the appropriate size. Hindsight I would have sourced terminals from bradrs/Sheridan Engineering. 91 transistor have a GM style connector, just like the 2G MAF, so they will always be easier to source from multiple companies.

It very likely is two cylinders, now that you mention it.

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No colors anywhere, I want them painted Black.