Bottom of coil (HEI ignition)



Carbon contact button between coil and rotor



Coil mount side of cap.

I think I may have identified the problem...

The procedure is every bit as much of a pain in the ass as I expected, but I'm having an unusually calm day, so spending 2 hours just getting the wires and cap off hasn't bothered me. Much.

The wires were routed under, behind and around every freakin' thing in the engine compartment, plus the multitude of plastic wire looms were old and brittle and every one of them broke when I popped them open. I will be going aftermarket and re-routing the wires when I reinstall them.

Now to go back out and actually take the plugs out...

So a cylinder wasn't firing.

What is that part?

quote:

Originally posted by Mars_Attacks:
So a cylinder wasn't firing.

What is that part?

I edited the original post. Should have labeled them to start with.

I'm guessing an ignition coil.

That looks like the giant HEI distributor with the coil in the top of the cap. It was introduced in 1975. I didn't think a 1990 would still use this. That isn't normal wear and tear.

Is the ground strap missing? It is sandwiched between the coil and cap and goes to the center of the three-wire connector. It is a common mistake to forget it. If it is missing, the coil will run in reverse polarity and will burn up in ~100 miles. I haven't dealt with an HEI cap for many years, but am 98% sure the rubber washer goes in the cap first, then the carbon button. A little bit of dielectric grease between them won't hurt. This keeps the button more firmly pressed against the rotor. If reversed it won't touch the rotor at all, eventually "zorching" a hole through the center of the rotor. Either condition will cause this meltdown.

AC Delco D336 distributor cap and D433 rotor IIRC.
Check for a missing ground strap as egregore mentioned.

I used to put dielectric grease on the silicone washer. Does not look like anyone did the last time. Should be included with the new dist cap.

At least the clam-shell hood provides easy access to the area where the distributor is located, which is only quasi-trapped behind & somewhat under the plenum of intake manifold.

Step over the tires put your legs between the chassis and tire and you have a nice seat the clamshell does make all the difference.

If you are not doing performance upgrades, go OEM on the coil, plugs and wires, JMO.

Wait until you get to number 8 to do any cussing, you'll need all your lungs and vocabulary to get between the AC housing and the engine. A piece of rubber hose/tube will be your friend, slip it over the plug. The rest will be easy as pie.

quote:

Originally posted by HRK:
Step over the tires put your legs between the chassis and tire and you have a nice seat the clamshell does make all the difference.

If you are not doing performance upgrades, go OEM on the coil, plugs and wires, JMO.

Wait until you get to number 8 to do any cussing, you'll need all your lungs and vocabulary to get between the AC housing and the engine. A piece of rubber hose/tube will be your friend, slip it over the plug. The rest will be easy as pie.

Indeed.

6 of the 8 plugs changed, just #2 and #4 to do after lunch. So far, a combination of wobble extensions and a U-Joint have gotten me onto all the plugs. Putting the new ones in is darn near as much of a challenge as getting the old ones out. The 4" piece of vacuum hose over the end has saved my bacon on 6 and 8. Only dropped them once each. Having a seat on the passenger's side front tire helps too. Didn't take long to figure that one out...

Can't see shit and the plug holes are at a compound angle (forward or rearward, and down) so getting the threads started takes some fiddling.

Electrodes on the old plugs looked pretty good, nice color, not eroded.

The ground strap was there on the old set up and was cleaned and moved to the new cap.

So your vette has the older big hei distributor with the coil in the cap?

I had a 1989 iroc camaro tpi engine that I put in a chevelle, and it had the small cap hei with an external coil. Like in the link below.
I wonder if your distributor has been changed.

https://www.jegs.com/i/JEGS/55...U9TqX3MaAu6GEALw_wcB

Yes, the coil-in-cap version. I'm fairly sure it's original, based on how everything was routed and the way the wire looms were set up.

If I was inclined to seek more horsepower/performance (I'm not, for both philosophical and financial reasons) that ignition would be the first thing to go.

egregore is correct about the contact, silicone washer and dielectric grease.

HEI distributors produce up to around 50k volts so they can jump some pretty impressive gaps, not that unusual for the carbon contact to be missing inside the cap and the car still runs. Saw one once that the contact was burned up, arced straight to the rotor and burned a hole in the distributor cap about the size of a dime. Still ran albeit with a miss too.

That being said I’d look into a different brand of distributor cap instead of AC-Delco. MSD, Echlin, and I preferred to use anything but an aluminum contact cap. AC-Delco in a nutshell is a marketing company anymore, they buy items on the open market that meets their minimum specs,box and ship it. The old days of the “Delco Remy” name meaning quality is gone. Today you’re lucky if the part says “Made In USA” on it.

I spent 8 years working at a Wire & Cable company, specializing in making everything found under the hood. One of our items was spark plug wires, in every way/shape/form, some labeled with a major automotive parts supplier's name, some with our own brand name, some sold in bulk to OE vehicle manufacturers. My take-aways:

As long as the "wire" (some were not wires at all, simply conductive rubber over a fiberglass filler) shows conductivity at 10,000 ohms per foot or less, the wire is good to go presuming there are no breaks in the insulation. We even sold some wire sets at up to 15K ohms/ft but that was in premade sets for new vehicles, not in our replacement part lines. Replacing a wire set just "because" is not a wise use of resources.