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Spark Plug Gap

syndicate1

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Hey guys! I know this has been discussed and would appreciate your help to clear up my own confusion.

I’m planning on replacing the spark plugs this weekend. I’m the 2nd owner and my EB is an original California ‘74 Explorer that is as original as can be. The only modification to the engine is the emissions controls have been removed. The 302 has been rebuilt, bored .30 over with stock cam done by the PO. I rebuilt the original carburetor and had the top end rebuilt 2.5 years ago (valve job, machined heads, timing chain, etc..). The oil pressure and compression are very good and from what can tell it has electronic ignition.

I’ve read posts and write-ups that suggest setting the spark plug gap at .035 points and .044 electronic ignition.

Here’s my confusion, the original valve cover sticker states that the spark plug gap should be .052 - .058.

Please be my second set of eyes and tell me if have points or electronic ignition? Should I set the spark plug gap according to Ford’s valve cover sticker or something else?

Thanks!

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cs_88

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That's the Ford Duraspark electronic ignition.
'74 was the first year for EI in Broncos.
Everything I've ever seen says .044" for EB's with Duraspark but it wouldn't hurt to run .035" either.
 

Rustytruck

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the sticker on the valve cover is what your supposed to run but the tune will last longer at .044 as this is for standard old style plugs that wore out in 30,000 miles. if you using platinum or iridium plugs then go for the wider gap. that California special emission engine has quarks the other states didn't have and a very lean fuel mixture need large gap to fire our crap fuel.
 
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syndicate1

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the sticker on the valve cover is what your supposed to run but the tune will last longer at .044 as this is for standard old style plugs that wore out in 30,000 miles. if you using platinum or iridium plugs then go for the wider gap. that California special emission engine has quarks the other states didn't have and a very lean fuel mixture need large gap to fire our crap fuel.


Tell me about the quirks!! It runs super lean. I’m running Autolite 45 spark plugs. Will the engine run better or worse if I still go with the larger gap that’s stated on the valve cover sticker?


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spap

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You can riches it up and run the wider gaps, just helps ignite the mixture better
You can experiment with a spare plug let the engine with a plug laying on the valve cover and watch the spark at different gaps see if .50 has a strong spark, if not close it up between .44 /.50 should be good
 

jckkys

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I can't explain why the valve cover decal has one spec and every other source has another spec. There is really is no good reason for it. The '74s and '75s were called Breakerless not Duraspark II. '77 was the first year for Duraspark I and II. The Duraspark I was only sold in Cal. for '77-'79. That system called for a plug gap of .060". Duraspark II was introduced in '77 tho the '76s used all the same parts that had the same specs as the '77s. Ford still called the '76s Breakerless. All the electronic ignitions except Duraspark I used the 0.044" gap. You may want to read this;https://pantera.infopop.cc/topic/duraspark-vs-msd-distributor. It's long but informative.
 

DirtDonk

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What color is the ignition modulator's wire strain relief? Maybe even though it's a 74 it could have had one of the oddball CA-only units that was what, the Yellow or Red grommet model? Perhaps that's why it's listed, and maybe the same as what you're quoting for the first gen Dura Spark?
First time I've seen one with gaps that big too, but I've learned to not be too surprised at stuff back then.

But here's the kicker I think. You said all the smog stuff has been removed? And you're not even running the specified plugs anymore? Well then I think you need to re-visit the carburetor jetting and the plug gaps.
Especially if you're running a replacement module with a different color grommet.

Everything else is non-stock now, so your gaps might have to be too.

Paul
 

jckkys

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The '74 module had a black strain relief, as the Pantera forum thread stated.
 

Broncobowsher

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When the electronic ignition came out industry wide the plugs gaps got wide. The emissions killed cylinder pressure which further allowed wider plug gaps. Some of these low cylinder pressure emissions turds had plug gaps of .080"

Your desmogged engine with a good timing chain (and not the factory retared timing chain set) should have a little better than stock cylinder pressure. I would run a little less than the label gap.

The really fat gaps only lasted for a few years. The gaps that grew as the plugs wore made issues. Even when things were good there were issues of burning up the center electrode on the cap.
 

ared77

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"issues of burning up the center electrode on the cap"

I used to work at a company (80's and 90's) that ran a fleet of GM vans and Broncobowsher is right, saw bad caps many times stop them dead. High voltage would run down a carbon track to ground rather than try to jump that big spark plug gap. Kind'a like me, always takes the path of least resistance! %);D
 

Broncobowsher

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And while you are at it, the vacuum advance should be hooked up to the pickup plate. The clip is missing. You will need to reset the timing as it will be way off once hooked up.

After you do that remove the rubber cap on the second port of the vacuum advance. That will let the chamber breath and allow the vacuum advance on the other side to work. If the vacuum advance is bad (very well could be after 45 years) just get a single port vacuum advance.

Also re-route the vacuum line for the brake booster so it isn't interfering with the throttle linkage.
 
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syndicate1

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And while you are at it, the vacuum advance should be hooked up to the pickup plate. The clip is missing. You will need to reset the timing as it will be way off once hooked up.

After you do that remove the rubber cap on the second port of the vacuum advance. That will let the chamber breath and allow the vacuum advance on the other side to work. If the vacuum advance is bad (very well could be after 45 years) just get a single port vacuum advance.

Also re-route the vacuum line for the brake booster so it isn't interfering with the throttle linkage.


Thanks for noticing! Can you tell me or mark up the picture to show me the vacuum advance should be connected to the pick up plate? And the missing clip? I’m far from an expert and still fumbling my way around things.


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Broncobowsher

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Your 3rd picture. there is a rod coming out of the vacuum advance. Has a hole in it. About half an inch in front of that is a pin. The pin should be through the hole.

The pin has a groove in it. there should be an E-clip in that groove. Sorry, don't remember the size of the pin. Most good hardware stores (not home improvement stores, real hardware stores like Ace) will have bins that will have the clip for pennies.
 
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syndicate1

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Your 3rd picture. there is a rod coming out of the vacuum advance. Has a hole in it. About half an inch in front of that is a pin. The pin should be through the hole.

The pin has a groove in it. there should be an E-clip in that groove. Sorry, don't remember the size of the pin. Most good hardware stores (not home improvement stores, real hardware stores like Ace) will have bins that will have the clip for pennies.


10-4! I see what your talking about. Will fix that and the timing then uncap the second port. I’ll also reroute the brake booster vacuum hose. Much appreciated and enjoy a virtual beer on me.


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syndicate1

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Your 3rd picture. there is a rod coming out of the vacuum advance. Has a hole in it. About half an inch in front of that is a pin. The pin should be through the hole.

The pin has a groove in it. there should be an E-clip in that groove. Sorry, don't remember the size of the pin. Most good hardware stores (not home improvement stores, real hardware stores like Ace) will have bins that will have the clip for pennies.


HOLY CRAP!! Reattaching the vacuum advance to the pickup plate and installing a 1/8” E-clip to hold it all in place has fixed my engine woes. I don’t think I need to reset the timing because now the engine runs like new and purrs like a kitten, just like it did after the top end was rebuilt. It even regained lost power and the exhaust doesn’t sound like an idling speedboat.

A little back story, over the past several months my EB has been gradually running rougher by the day which is the reason I decided to change the spark plugs, thinking they were fouled up. Based on reattaching the vacuum advance, I’m guessing the timing was gradually moving out of alignment.

@Broncobowsher You made my week. I can’t thank you enough for seeing the detached vacuum advance in the picture AND letting me know. The devil is in the details and all it took to fix it was a $0.33 1/8” E-clip!

While I’m at it, I’ll still replace the spark plugs and set the gap at little less than the recommended gap that’s printed on valve sticker.

Here’s a pic of the fix...

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syndicate1

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When the electronic ignition came out industry wide the plugs gaps got wide. The emissions killed cylinder pressure which further allowed wider plug gaps. Some of these low cylinder pressure emissions turds had plug gaps of .080"

Your desmogged engine with a good timing chain (and not the factory retared timing chain set) should have a little better than stock cylinder pressure. I would run a little less than the label gap.

The really fat gaps only lasted for a few years. The gaps that grew as the plugs wore made issues. Even when things were good there were issues of burning up the center electrode on the cap.


To answer your comment- yes, a new good timing chain set (non factory retarded) was installed when the top end was rebuilt.

I installed the new plugs with the gap at .050, just below the recommended range stated on the valve sticker. HUGE difference! The engine starts right up without a full turn and it runs/drives perfect. The throttle response seems to be better as well.

For comparison, I checked the old plugs and they were set between .040 - 044.

Thanks again!


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