Originally Posted by hp_lovecraft
In my case, if I start, and drive with fairly little throttle, I do not notice any misses at all. But if I open the throttle up beyond say 1/2 full, it starts to miss in 3rd or 4th gear. This usually happens if going up a hill, or trying to accellerate.. The misses seem inconsistent, unless I'm at WOT then it seems worse like a cylinder is consistently missing. (like when a modern car hits the rev limiter)
It also misses if I lug the engine down to 500rpm or so.
I'm not a HEI fanboy. I bought one simply because my prestolite was failing (and was a mess to begin with thanks to the PO). Its worked for the last couple of years. I have not replaced the wires because they seem fine. Bought them at advance or autozone.
I'd be happy to replace them, but any way to test them? I guess my next step is a proper compression test. I still wonder if the problem is in the ignition. The wear on the contacts looks very odd. There is burn marks right on the very edge of the contact, but not in the middle like it usually is. I'll get a picture tomorrow.
I don't think its running lean. I've had lean problems before (bad vac leak, and bad timing). Both times the engine ran wicked hot. Engine is running cool now.
Sounds like you have two issues,
One is rotor phasing,
The rotor is on one side of the plug terminals when the ignition fires, then the spark has to 'Jump' to the edge of the terminal it's already passed, or is coming up on....
You can EASILY fire the wrong terminal when this happens.
Also sounds like you might have an aluminum terminal cap if the firing pattern is that obvious.
Aluminum burns up into aluminum oxide when high voltage hits it, and becomes NON-conductive for high voltage transfer.
There is a reason I preach BRASS TERMINALS, they don't burn up like that and become non conductive.
Rotor phasing problems happen when the rotor is out of 'Sync' with the plug terminal when the ignition fires...
As vacuum advance comes in, the rotor gets farther and farther away from the proper plug terminal, and that drives the firing voltages WAY UP, unnaturally high.
When it has to jump a big gap, all the energy the coil is producing has to go to voltage to ionize that huge gap, and there isn't anything left over for Amperage (Heat) or Duration (The time the spark lingers in the gap).
Rotor phasing usually has two common issues when it's way off,
One is the vacuum advance is hooked to manifold vacuum, yanking it around to full advance virtually all the time,
And the second is the distributor gear is usually on the wrong side of the shaft.
These distributor gears have 13 teeth, and normally the 'Discount' gear places don't pay much attention to where the gear needs to be to keep the rotor aligned...
(Most of the 'HEI Clone' makes have never heard of rotor phasing, so they have no clue... They are just assembling 'China' parts and not paying attention to the results).
When you go up a hill, or try to accelerate slightly in traffic,
Your fuel mixture is at it's LEANEST,
If you have large tires, your engine has slowed down much more than it was intended to at this particular MPH, so you are having to 'LUG' the engine more...
Add in a bunch of timing, you get a 'Bog' or 'Hesitation' people often call a 'Miss'...
It's simply too much load, too lean of fuel mixture, and too much ignition timing...
If you wan to prove it to yourself, take the vacuum line off the distributor and plug it,
Then go lug the crap out of the engine someplace to see if the 'Problem' happens.
IF your issue goes away, then you found out there is too much ignition timing staying in the curve WAY TOO LONG...
If you tune the distributor to DROP timing when you crack the throttle blades going up a hill, or trying to keep up with traffic in high gear,
Then you won't have those issues....
Most people jack in WAY too much 'INITIAL' advace, 6 degrees is plenty for a good idle,
And then they hook these things up to manifold vacuum, which usually pins the vacuum advance in FULL all the time.
The vacuum advance is supposed to 'FLOAT' with load.
When load increases, vacuum drops, and the vacuum advance is supposed to drop some timing.
If it doesn't, you get a 'Bog' or 'Miss', when it's mild,
And when that detonation gets really bad, you get 'Spark Knock'...
The engine won't live long if you get 'Spark Knock', but even the 'Bog' or 'Miss' will damage the engine over time...
Do you have any idea what vacuum signal you are pulling at PTC (Part Throttle Cruise) before you tip into the throttle a little?
What does the vacuum drop to when the 'Miss' is most prevalent?
Once you know where the vacuum threshold is at PTC,
Then you can use a hand pump, vacuum gauge & timing light to set up your vacuum advance to DROP some timing in that range, and your 'Miss' will reduce or probably go away...
As for plug wires, GOOD ONES will come with a spec sheet that tells you how many 'Ohms' per foot of wire.
(Ohm, a measure of electrical resistance)
That's a start.
Personally, I slap a good set of wires on to start with instead of the 'Replacement' wires made in China you get from the parts stores.
Even if they cost you $100, that's $10 a years for the next 10 years you don't have to worry about them,
While the 'Discount Sore' wires will fail anywhere from out of the box to about a year... and they run around $50 anyway, so they aren't cheap...
I test wires under load, but not everyone has a distributor machine...
I can usually load the 'Replacement' wires enough to make them fail completely, or catch them on fire!
You can't do that with an MSD set of 'Cut To Fit' wires with good wire, good terminal and good boots...