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Discussion Starter #1
2.3 duratec. Occasional miss at light accel. turned into a worse problem on a 15 mi. trip. New plugs seemed to solve it (AR103, .055" gap).

Longer drive tonight, started to do it again after a dozen miles. Stopped for a fill up, got quite bad after another 15 mi. (missed worst at light accel.).

Hard accel, runs on three then picks up & goes OK. Worst at lower RPM, med. accel. Idle starts missing once it gets bad.

Coils/boots didn't look bad when plugs were changed, I'll have to look at them again in the AM.

This looks like another one to drive 'till it's messing up then start checking - loads of fun!

[cheers]
 

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Occasional miss at light accel.
You mention 'miss' several times; and these are without any DTC's right? Any scan tools on hand? Are these symptoms all butt-dyno?

Miss to me usually means spark; any chance yours might be compounded by a fuel or air issue?

If worse after spark plug replacement; always return to the scene of that crime... COP's, boot health, COP springs & contact points?

Geeeez, I hope you do not get what my car has; -still unknown.

Nice that you shared, especially since you pretty much own this place.

Cheers! -back at you
 

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Vince your Moderator
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Tps, cps, maf????

Check the pigtails Roger
 

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If pretty sure it drops out to only three then comes back then almost gotta be ignition issue...........maybe check coil resistances.
 

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Fun fact # 1: resistance increases as heat increases. A marginal coil that makes an adequate spark when cold may have too much resistance once hot to ignite the air/fuel mixture.

Fun fact # 2: a lean air/fuel mixture (at idle, low load) is harder to ignite than a rich air/fuel mixture (under load).

Don't know if that will help you at all.
 

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Often the coil has a short or open that does not enable until temperature warps things more.........
 

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Discussion Starter #7
Thanks for the thoughts, adds a bit to my list of possibilities.

Earlier in the year I had an intermittent with the IMRC (tumble flaps) that took a while to trace . Couldn't find the vacuum leak for that one until it got bad enough to be consistent. (could have another leak too small to be obvious yet)

With this fun I did have a misfire code before the plug replacement, hasn't been bad/consistent enough for that to come back yet .

Not seeing anything strange yet with the code reader/scanner, but it wasn't bad in the 20 miles of testing I put on it earlier today.

Coils are a suspect as well, but with four pricey ones I'm not throwing one or more at it until I can prove a problem there.

When it's not bad like today, the best description is an occasional stumble/miss on acceleration and it's NOT it's usual self of being impervious to excessive throttle at lower RPM. Stomp on it & it'll stumble/miss 'till it finally catches.

Once it gets worse again it should be easier to diagnose, I'll keep looking at this & that until what's wrong jumps out at me. Vacuum leak is high on the list.
 

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I know what I think about those tumble flaps.............and not printable.
 
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