Hi

Right... i know this question has probably already been asked a thousand times and numerous different answers have been given, but what is the CORRECT spark plug gap to use on a Focus.

Is 1.0mm right as my local ford garage state 1.3mm is what it should be, but the ngk's in my 1.6 petrol focus are at 1.1mm.

What is the big factors with these varying gaps.

Does one give more power, smooth, less misfires. better mpg etc.

My car has been running smooth for a while , but recently the hesitation and random misfire has returned, its still very intermittant as sometimes it runs as smooth as silk.

It has had new leads coil pack and plugs a short while back. Might recoat the leads with dielectric grease again.

Any ideas on any of the above would be very helpful.

I believe they changed it at some point and then changed it back again something to do with coil pack failures my ngk's are at 1.3 everthings fine. 1.1 is recommended for iridium plugs iirc

Sent from my GT-S6810P using Ford OC mobile app

!st thing is there is no "correct" spark plug gap - 1.3mm is correct - 1.1mm is "correct" 1.0mm is correct 0.8mm is "correct"

There is a manufacturers recommended gap - but as J has said, that changed from 1.3mm to 1.0

Another thing to point out - as the plug wears the gap gets wider

A wider gap gives a fatter spark, this is better for emmisions as it burns better it can improve performance very slightly provided the spark can jump the gap

But a wider gap puts the HT (High-Tension or high voltage) part of the ignition system under more stress, the spark tries to find the easiest path, (like lightning) so when the plug gets worn, or coked up, or the leads get wet, the easiest path may be the leads, or inside the coil packs

So a narrower gap means the spark is more likely to occur where it is supposed to, at the spark plug tip, even when the plug is worn, coked up or the HT leads are wet, dirty or the system is not in 100% tip-top condition

In a nutshel the gap is a compromise between, reliability/ longevity(which means how long the plugs/ coil packs last) = narrower gap, and emmisions/ performance (though the performance advantage is slight, and the system has to be in good condition) = wider gap

Personally if i was running an older petrol-engined car i would run a narrower gap,(eg 1.0mm or 0.9 to allow for wear) or keep a few sets of plugs/ coil packs handy for when, oops i mean if, they fail