Terribly running 1995 Chevy Van

1995 Chevy Van, 5.7L
Was running well recently, on a custom chip. Then things went to shit, and in the process of evaluating things, I've gone back to the stock chip, and stock timing. The engine is not original. It's a L31R short block, stock cam, with Summit Al heads (vortec style chambers), and a modified TBI and intake. Upgraded GM performance fuel pump. A lot of overkill parts....and I recently switched back to the stock chip, because I didn't want to have to modify the timing every time I smog the vehicle.

Symptoms - missing badly, sometimes pinging, sometimes clanking (which I suspect is predetonation). Misses at idle, under partial load, and under full load. Under full load is when I hear the clanking. Shakes/shudders and is lacking power. Cannot maintain 65 uphills. It also developed a high idle, which I suspected was a IAC, but I was not sure how to test it. I brought it to my mechanic, he confirmed a bad IAC and it was replaced. He said it ran great, pick it up, and the thing still runs like crap, but it idles where it should now.

Plugs show a rich condition. One of my mechanics said to change the plugs when I showed him the picture.

Then I found your site, and thought I would try the rpm drop, pull the plug wire technique. I got shocked! Through my rubber glove, with the probe right there. Anyway, the spark jumps through the cap, anywhere on the cap. It arcs when you put the probe anywhere near the cap and wires. And sometimes if you put your finger near the cap (like when trying to grab a spark plug wire boot), it jumps through the cap into your finger! I didn't finish the test because I didn't want to be shocked again.

Is this normal on a relatively new cap for a chevy? I attached pics of the state of the cap and rotor and some of the better and worst plugs.

I am planning to replace the plugs, with some recommended when using AL heads from this site:
www.onallcylinders.com/2018/05/11/ask-aw...ark-plug-heat-range/

Is the state of this cap and rotor bad enough to warrant replacement?

What other checks would you recommend?

I replaced all the plugs. I had the same # autolites in there already. Some of the plug wires don't feel particularly tight fitting, but I've put them all in there. I also cleaned the carbon off the rotor.

It feels a little bit better, yet the miss is still there. It gets worse as it warms up. The plugs were a bit cleaner when I took them out, than the last time I checked them.

How long did it take to get the plugs that black? Also do you have any type of scanner that can look at oxygen sensors and coolant temperature sensor data with fuel trim data

Any feedback on the arcing through the cap? Is that normal?

I replaced the plugs, here are the pictures of the plugs as I took them out. They were the same # plugs as I installed. One had been replaced previously, in cylinder 7. That was the only one with a washer. Should the plugs have washers when put into aluminum heads?

Plug 5 is the worst pic, but it also looks pretty black, probably the worst. But these don't look terrible to me.

The engine was professionally rebuilt and started for the first time 24 months ago, I've put 14k miles on it since then.

Arcing through the cap is not normal. I would recommend replacing cap n rotor n possibly the ignition wires.

Cap has a crack letting high voltage to outside ? By the looks of the internal contacts...they are pitted...rotor also trashed......coil is putting out too much voltage ?

Tighten intake manifold bolts...common vacuum leak area that causes all sorts of issues.

Matts Auto wrote: Arcing through the cap is not normal. I would recommend replacing cap n rotor n possibly the ignition wires.

What he said

Those engines are known for distributor caps that cross fire when they fail

I learned more about the cylinder drop test by watching ScannerDanners youtube videos. He was shocked like I was, and then found it was arcing through the opposite end of the cable. I gave that test another shot, and discovered a bad spark plug cable on one cylinder. I also found the arcing through the cap stopped when I replaced that cable. Upon closer inspection, I believe it was arcing from that same terminal along the surface of the cap to the test probe....

It's running really well, I drove it about 60 miles yesterday. Thank you ScannerDanner and to the forum!