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Discussion Starter · #1 ·
..., and this time I'm sure it's not the dizzy since the troublesome OEM dizzy was replaced with a Pertronix less than 20k miles ago.

It's a regular, consistent miss at startup, at least one but maybe 2 cyls.

How often do you guys replace the spark plugs? The wires were new with the dizzy, but the plugs have WELL over 30k miles on them. I pulled (1) a month or so ago and it was burning picture-perfect, but that was 1 of 8, so maybe I should just replace them all?

Unless a bad wire, I don't know what else to check. No codes on the diagnostic window under the Pass seat. Guess I'll replace the plugs and report back.
 

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Generally think they'd easily get 24,000 miles but 36,000 probably a far limit from experience. May depend on ignition system and erosion of electrode at far reaches of practical life with more laboured starting one of the characteristic I've seen. Not necessarily a misfire, but reluctance to pick up promptly hot or cold.

I had similar symptoms on mine that took a while to trace (just one not running for first few minutes) and finally found a break in HT lead #1 at plug cap terminal. I use carbon silicone leads and that one had broken at it's joint to the brass clasp that connects onto plug terminal. You could see a carbon track trace across the gap where it would run (I guess more favourable cylinder conditions as it came back from full rich starting will reduce plug gap resistance such that the poor gap could transmit) I cut it back and remade the lead connector and it's been fine for last 6,000 miles.

Firstly at cold start I'd run it for 30 seconds and switch off, then feel the exhaust ports with your fingers to identify which one or more are cold. Then you can at least target the right components to see if you can fix easily.

Experienced problems with a new HT lead sometimes (they are not always out of the equation) not often but worth not discounting it else you'll chase your tail. If you've got a cylinder definitely reliably cold, then it's usually one or t'other plug/lead.
 

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Discussion Starter · #3 ·
UPDATE: Used the cold start/30-sec run procedure and was AMAZED at how well it worked.....3 cyls dead cold at the exhaust manifold. 30 sec is a good time, any longer and you'd likely burn your fingers on the good cyls.

Pulled the cap and cleaned rotor pickup areas, put it back together with no change. Got new plugs in the mail today, will swap them in with fingers crossed nd report back.
 

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Strange, do you mean the cylinder isn't firing (combustion) or can you not see a spark at the plug if it's tested by being held against the cylinder block ?

Potentially two different things and reasoning.
 

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Discussion Starter · #6 ·
The cyl isn't firing, evidenced by:

1. NO change with a new gapped plug and a new wire
2. Running cold engine for 30 sec then shutting down, every cyl 2 thru 8 was warm/hot to the touch @ the exhaust stub, #1 was cold before & after plug/wire change
3. Timing light clipped to #1 plug wire shows NO "flash" with engine running.

I have not used the age-old method of holding the (new) plug to the head while cranking over because the #1 plug came out with extreme difficulty, as if the threads were galling with the head for the entire thread length, and the new plug went in (with moly lube on the threads) with excessive difficulty also. I am reluctant to take the new plug back out.

Did I mention that this was a Pertronix dizzy? Yes, the OEM dizzy was replaced over a year ago, and it's purred like a kitten UNTIL NOW. I know Pertronix has a large history with replacement dizzys all over the automotive map, and some people swear by them, some hate them. I was desperate for a fix for the major PIA OEM setup that I had continual trouble with, so here I am.

I suppose the next obvious thing is to suspect the dizzy cap, and replace that?
 

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Yep, I wouldn't take that plug out unnecessarily either.

I don't know if it would not give pulse signal for timing light if plug had a fault though. You could use a spare plug clamped to an earth to see if that sparked / produced pulse though.
I'd agree with you in now suspecting the cap though as there's not many places a single absent spark can go to.

Are the caps expensive for that distributor ?

Before that, could you swap the wire for one of the others to see if the cold fault moves too. Think number three might swap or both at least similar length to switch them for each other's position both ends.
 

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Discussion Starter · #8 ·
You could use a spare plug clamped to an earth to see if that sparked / produced pulse though.
Why didn't I think of that. Duh. I have 8 spare plugs still sitting on the bench.

The cap fits the dizzy the same as OEM, I remember because when the shop installed the Pertronix, they did NOT install the Pertronix cap, they got lazy and didn't want to swap wires to the new cap so they just installed the OEM cap. Ran fine, but I had them swap to the Pertronix cap. I'll order an OEM-style cap just to eliminate THAT factor and report back.
 

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In reply to spark plugs, cheap-o Champion copper plus changed once a year. Easy to remember replace before MOT
 

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The cap fits the dizzy the same as OEM, I remember because when the shop installed the Pertronix, they did NOT install the Pertronix cap, they got lazy and didn't want to swap wires to the new cap so they just installed the OEM cap. Ran fine, but I had them swap to the Pertronix cap. I'll order an OEM-style cap just to eliminate THAT factor and report back.
On my 92 (240k mi), the cap and rotor are the first thing I have to change out, and I always have a spare in the car because they like to leave the Rangie stranded not starting. I'd suggest trying to get OEM cap/rotor if possible. Non-OEM sets seem to be the worst in terms of longevity.

-Mike
 
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