Pancake Distributor Disease
Ah yes, the dreaded pancake distributor disease(PDD) again on GM Vortec Engines.
This is a cap for the pancake style distributor used on 96 and up Astro/Safari vans.
What is this random bucking/misfire feeling thing happening to my Vortec powered van? It usually shows it's ugly face when you are in OD with the TC locked up at partial throttle on a nice flat highway. Press on the gas it stops, let off the gas it stops, partial throttle it comes back.
Usually the bucking/misfire is worse in high humidity and rainy situations because the secondary ignition system is working on the very edge of failure. Can even cause a hard/no start condition. Sometimes it just shows up as a p0300 random misfire code, other times there is no code at all.
It's annoying, and it's costing you fuel mileage. Worst case is you ignore it and destroy your catalytic converter from the excess un-burned fuel heading into the exhaust, CatalyticConverterDeath. Plus your secondary ignition system is working harder which is really hard on your ignition coil, ICM, as well as the cap/rotor/wires as the energy is increased to try to overcome the added resistance(in the form of an additional gap).
You replace the cap/rotor and it goes away for a little while, but then the symptoms return and you think to yourself, damn maybe they were right and I should have used a GM/ACdelco cap and rotor. So you go and buy a GM cap/rotor and it's fine for a while but then it starts happening again. While the new cap and rotor temporarily relieve the symptoms it definitely is not the cure.
Most likely it's the gear at the bottom of the distributor, the original was made with a softer metal that wears prematurely and the replacements are made of a harder metal. You can buy just the replacement gear(~$40-55 ACDELCO 10457356), or you can replace the whole distributor/cap/rotor for ~$50. My favorite that has been super reliable in many vehicles is 6671-BK from Skip White Performance, either from their site, ebay store, or by phone at ---removed---. It appears that Skip White no longer imports/stocks this particular distributor.
Note: It seems that there are some new versions of the distributor floating around, which may or may not be of the same quality as the distributors of the past. Buyer Beware.
You can always search eBay/Amazon/etc for the part number 6671-BK or ARC 1326202. http://amzn.to/2p8Coee Sometimes you will find them under 671-BK, or variations around that. Also see https://amzn.to/3l3v3M3
Also, you may find that the drive gear is 180° out, not common but could happen, requiring you to remove the pin and rotate the gear 180°. https://www.astrosafari.com/threads/distributor-install-issue.144446/post-1567988
Note, some will say just grind a bit off of the distributor hold-down so you can adjust the 'non-adjustable' distributor. I wouldn't want to run on such thin gears, eventually it will leave you stranded. Here is a well worn, problem causing example:
When the distributor drive gear is worn down, the rotor will lag behind where it really should be, causing a larger gap between the two:
MSD Has a great video about phasing the rotor, they cut a hole in the cap so you can see the spark jumping from the rotor to the cap. They are of course advertising an adjustable rotor, but it gives you a great visual on what is happening when it's out of phase due to a worn drive gear as well.
Below are two short videos showing the play in the distributor drive gear, you do not have to pull the distributor to check, simply pull the cap. While you are in there, also check the cap and rotor for cracks, chips, corrosion and carbon lines.
Too much play in the rotor
Just right :)