Spark plugs...SP578 CYFS12YRT3 versus SP594 CYFS12Y

[Msfitoy]

I can't seem to find a definitive answer...is SP594 CYFS12Y ok to use?

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[Apples]

The 578 is the correct one. This said, there is a replacement number (594?). In any case, I'd check with your dealer's parts folks.

 

[Msfitoy]

The 578 is the correct one. This said, there is a replacement number (594?). In any case, I'd check with your dealer's parts folks.

This is what's on order...confusing right?

 

[deleriumtremor]

This is what's on order...confusing right?

I think the 594 is the max endurance plug "Ruthenium", whatever unobtanium element that is, IDK?. The 578 is the Iridium version. Just FYI, Rockauto is about 25% less than what you have pictured on Amazon for the 594 plug. Of course, you have to get more stuff to justify the shipping versus AMZN.

 

[Msfitoy]

Found it...from 5 Star Tuning:

" Part number SP- 578 has been superseded by Part number SP-594"

https://5startuning.com/product/201...torcraft-iridium-spark-plugs-set-of-6-sp-594/

 

[4rd SVT]

Throwing a "wrench" into this conversation...

Tune+ NGK 1-Step Colder Pre-Gapped Spark Plugs

I have a set in my RS, and seems to ide & drive smoother...
My plan is to order a set & at some point, swap these in.

I'm gonna contact them to see if there's a difference in gap for the Ecoboost-Mustang & RS version of the 2.3L specs... so I know which version to order.

 

[Grandaccess]

Throwing a "wrench" into this conversation...

Tune+ NGK 1-Step Colder Pre-Gapped Spark Plugs

I have a set in my RS, and seems to ide & drive smoother...
My plan is to order a set & at some point, swap these in.

I'm gonna contact them to see if there's a difference in gap for the Ecoboost-Mustang & RS version of the 2.3L specs... so I know which version to order.

When selecting your fuel, the difference will be the gap. If you intend on running
91-92-93-94 AND E85 then you will purchase the 91-92-93-94-E30 Plugs

 

[veloci1]

i just changed my sparkplugs (the original that came with the truck since new) on my 2020 XLT FX4 to SP594 . i drove around the neighborhood and everything seemed to be fine. once i got on the fwy and above 50 mph, the truck started missing. rough running. got off the fwy and under 50mph and everything went back to normal. i switched back to the old plugs and everything was fine. the SP594 plugs were gapped around .030. has anyone encountered a similar issue? i am trying to find some of the old SP578, but, no luck.

 

[Rp930]

i just changed my sparkplugs (the original that came with the truck since new) on my 2020 XLT FX4 to SP594 . i drove around the neighborhood and everything seemed to be fine. once i got on the fwy and above 50 mph, the truck started missing. rough running. got off the fwy and under 50mph and everything went back to normal. i switched back to the old plugs and everything was fine. the SP594 plugs were gapped around .030. has anyone encountered a similar issue? i am trying to find some of the old SP578, but, no luck.

The SP594 plugs are fine. It wasn’t the spark plugs. You probably didn’t have one of the coils installed properly.

 

[veloci1]

i tried that 3 times. i moved the SP594 from one location to another to see if it was one of the plugs. i even ensured #4 (many people mentioned the #4 coil not sitting correctly) and no luck. like i mentioned, went back t the old plugs and no problem. now i am searching for old stock SP-578.

 

[Rp930]

i tried that 3 times. i moved the SP594 from one location to another to see if it was one of the plugs. i even ensured #4 (many people mentioned the #4 coil not sitting correctly) and no luck. like i mentioned, went back t the old plugs and no problem. now i am searching for old stock SP-578.

My truck is running better than ever on SP594 plugs. Maybe you just got a bad one. SP594‘s are the supersession. I believe they are slightly colder but don’t quote me on that. It’s not the plugs other than maybe you got a bad plug.
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