Engine Spark Plug Recommendations

Discussion in '1994 - 1995 Specific Tech' started by hssnpny, Jan 19, 2013.

  1. Plugs have been in there a few years so figured I'd replace 'em. I pulled out autolite 3924. When I went to order the same plug since they were running fine, I noticed they wouldn't come gapped correctly, and weren't even a plug for the Mustang. Not sure why the last guy ran them.

    So, given my application, anyone have recommendations? Check my sig for bolt ons.

  2. Most of the aftermarket aluminum heads use the 3924 plug instead of the stock plug. I'd buy the same and gap them. That's pretty much what everyone uses. That or NGKs.

  3. Those plugs are needed for the aluminum head since they are a gasket style plug, not tapered like a stock plug would show. The 3924s work well but they are a little hot for me personally, the 3923 would be better if you want to stay Autolite. Personally Id go NGK #8 which is a great plug for a boosted combo, they are PT#7173 to most part stores, gap to .035"
  4. Rick, I thought the ngk 5671-9 was the plug to use?
  5. I run NGK UR45 in my AFR 185'S ????
  6. so after doing a little searching, the 5671-9 is one range colder than the 5671-8. time to cross reference to the 3924 which im running also but will need to go one range colder when i install the turbo
  7. One range colder than a 3924 is a 3923.

  8. yeah i know that the ngk confused me as theirs is opposite, the 9 is colder than the 8
  9. Yeah, NGK is backwards for no apparent reason.

  10. guys on te turbo forums recomendthe ngk 5671a-9 which i would say is the heat range of a 3922?
  11. 3923 is the coldest plug in that size /range from Autolite, one reason I switched to the NGK
  12. I replaced the spark plugs on a '006 GT that had 115,000 miles. (You can say it's almost 200k the way this one is driven!) The replacement plugs are Motorcraft platinum OEMs. And now for the serious part:

    If the spark plugs have been in there for a while you should be aware that a good amount of oxidation has formed and it will interfere with their removal. (See below) This is the flaw in what seems like a good design. You don't have to gap these and they have more conductivity than regular plugs.

    Before you start the job get some anti-seize product, WD40 or similar. As you remove each distributor spray the product into the cavity. Let it sink in for a while. After the commercial break start removing the plugs. Be careful and slow down if you hear a creaking sound - that's oxidation!​

    It's like a game of Operation (by Milton Bradley) except if you over-torque it you get a broken plug instead of a buzzer. Though you will still see a red light... be careful, Anger leads to the Dark Side. You see, the spark end is a porcelain segment inside of a metal sleeve which can break off where it connects to the plug's thread. So the upper half will exit leaving the bottom half unreachable. You will need a spark plug removal tool ($100 at Napa) - I tried everything else... EVERYTHING.

    It comes with instructions but it's basically two tools in one. First mode will push the porcelain downward and out of the way. Second mode will create new threads on the inside of the metal sleeve so it can be torqued in reverse and pull the sleeve out of the hole. Squint your eyes for this next photo.

    For first-timers: the distributor fits easily over the plug once the plug has been installed. The fastened distributor will keep the connection tight. Don't go listening for a Tupperware pop when you're replacing (reinstalling) the distributors over the plugs. Some recommend a gel to reduce condensation in there but gels are icky... you choose, I gave you Free Will.

    Ownership of the tool will make you king among men... well, among late-model Mustang owners anyways.

    PS: Most Mustangs I've come across seem to go 100,000 miles or more problem free with one or two owners. So suck it, Toyota. I hope this helps!