Read my spark plug...

[GasSavers_Erik]

Originally Posted by theholycow

If I had miswired the spark plugs (definitely possible, I lost my labels while changing them and had to do it from a chart) wouldn't it consistently run terribly?

Pull the plug wires one at a time while it is running to verify that the idle decreases (meaning that cylinder was firing before you stopped it)

[theholycow]

Since it's turned into troubleshooting my problems I moved the thread to Troubleshooting & Repair.

Anyway, there's a vacuum diaphragm attached to the distributor. I don't know what it's called. Do they fail? I imagine that if they do fail, they can be flaky rather than just always dead. Is there a way to test it?

Then there's this thing. One line goes to the aforementioned diaphragm, one goes to the manifold, and one goes to the carburetor. This is the thing whose rotten lines I replaced (I also removed its rotten boot). Should I investigate failure in this? (Lower left of photo, yellowed plastic thing)

[theholycow]

Originally Posted by Erik

Pull the plug wires one at a time while it is running to verify that the idle decreases (meaning that cylinder was firing before you stopped it)

It would be weird if I was running on 4 or 5 cylinders this whole time. I'll try that for sure.

[pgfpro]

Originally Posted by theholycow

I guess I'll pull the rest, and maybe I'll sacrifice one or two so I can autopsy like that. What's the best way to cut the thread off? My instinct is a cutoff wheel.

The cheap Autolites worked great for 30,000+ miles in my truck but maybe the Buick doesn't like them.

I think my cheap distributor cap may have been BWD. Anyway it might be time to invest in some better quality ignition parts, but I would just rather diagnose first before throwing parts at it.

If I had miswired the spark plugs (definitely possible, I lost my labels while changing them and had to do it from a chart) wouldn't it consistently run terribly?

The way I do it at the track is to chuck the plug into a drill and then put the drill in a vice or make a way to secure it. I then use a hack-saw to cut the thread part off with the drill at a low speed.

If you got your wires crossed it would run like crap. Unless as a example on a GM with the firing order 18436572 5 and 7 get crossed. Its just a very light miss.

[Jay2TheRescue]

Here's a good cure for purchasing Autolite:

From the makers of the infamous "Orange Can Of Death" comes Autolite spark plugs! If they think they can cut corners and use hot melt glue to manufacture an oil filter, what makes you think they can make a quality spark plug? Besides, even with your 30,000 mile history with them in the truck, the OEM Platinums will go 100,000 and beyond.

Find the OEM plugs on sale, and in the long run not only do you save money, but the pain of changing the plugs. Especially the #6 cylinder. That's a true pain on old Buicks as the A/C unit protruding from the firewall makes it darn near impossible to get a socket wrench in there and be able to move. I had a stubby extension about an inch or 2 long. It was the only way I ever found to do it and not take hours to get the last plug changed.

[GasSavers_Erik]

The diaphragm on the distributor advances the ignition timing under certain conditions- most of the time they operate on manifold vacuum and keep the timing advanced at idle but some vehicles use venturi vacuum or even ported vacuum. I think manifold vacuum is best from an economy standpoint.

They do fail first with a small leak, then with a big leak- just connect a vacuum pump and see if the diaphragm holds vacuum (it should). If it holds vacuum, then test the mechanism it by applying vacuum while you have the timing light hooked up- it should advance the timing.

The yellow plastic thing looks like a one way valve- like would be found on a brake booster hose. Hmm- or maybe it is part of the charcoal canister system for collecting fuel vapors from the carb or delivering them to teh carb to be burned.

[Jay2TheRescue]

I think it is part of the vapor recovery system.

[theholycow]

Jay, you make a good pitch against Autolite plugs.

The yellow plastic thing is not part of evap. It connects to the manifold, the carb, and the distributor's vacuum diaphragm. It is definitely part of the vacuum ignition advance.

[Jay2TheRescue]

I'm not sure what that yellow thing is then. I haven't had my 1980 Pontiac in nearly 20 years, and the 81 Buick is electronic advance. I could take a look at Rusty next time I'm down at Dad's, but I doubt there will be many similarities between a 1980 car and a 1986 truck.

[theholycow]

I googled for manifold and port vacuum (I think the line from the carburetor to the plastic thing is port, not venturi, but I'm not sure why I think that) and found this very educational post:
http://www.corvetteactioncenter.com/...m-advance.html

It makes a good case for running straight manifold vacuum to the distributor's diaphragm. It also mentions that port vacuum advance is for emissions, specifically the A.I.R. system which I have removed from my car.