Spark Plug and Ignition Wires Questions

I have a 1999 Ford Ranger that I recently bought used. I was going to change the spark plugs and possibly the ignition wires. A few questions first:

1. Is the extra money spent on Iridium and/or Platinum plugs worth it. I was considering using the Bosch Platnium IR Fusion plugs. But at $8 each, I don’t want to waste money if it’s not going to make very much of a difference versus a standard copper plug.

2. A friend told me to change the wires too. However, a mechanic friend of mine said it may not be necessary and suggested checking them first by misting water over the plug wires while the engine is running. Most of the guides I see on the internet say to use a multimeter to measure resistance. I don’t have easy access to a multimeter, so can I use the water mist method reliably? Are there any other tricks I can use to test the wire? Should I just go ahead and replace them and not bother testing them at all?

3. Any other tricks or tips out there for ignition system tune-ups in my truck?

If the spark plugs are easy to access then just go with regular plugs. Platinum plugs are used where spark plug access is difficult because they last longer.

If there were anything wrong with the secondary ignition system it would cause a misfire. And since the vehicle has the OBDII engine management system which detects for misfires, if the Check Engine light isn’t on, I wouldn’t mess with anything.


Iridium or Platinum plugs have one advantage over regular copper plugs…they last longer…NOTHING more…Not better performance…not bet gas mileage…they just last longer.

As for which brand to use…stick with Mopar plugs…Many plug manufacturers make plugs for many different vehicles, but they usually don’t do it as well as the OEM plugs. NGK would be a good alternative. Never had good luck with Bosch, Champion or Autolite plugs.

Wires: Visually inspect the plugs. Look for cracks. If you’re unsure then replace them. Don’t forget to replace the cap and rotor while you’re at it.

Don’t fall for the fancy plugs. They won’t do anything for you. What you want is just exactly whatever the OEM spec is. Some engines are picky & people put fancy plugs in and they make a mess. You can’t go wrong with the regular OEM spec.

Take the money that you won’t spend on fancy spark plugs and buy the wires - they’re not that expensive. You also don’t want anything fancy - but you don’t want bargain basement either. I also drive a Ford and the Motorcraft wires are not expensive.

If you really want to pinch you can mist them. But that will only tell you if you have a boot/insulation problem. It won’t tell you about resistance (which is what the multimeter is for). If the truck is running ok with new plugs and the misting shows no problems you won’t likely kill anything staying with the wires. How may miles are on the truck?

I picked up a perfectly good Craftsman digital multimeter for $20 at Sears. I use it all of the time for cars and other stuff. I also have one that only cost me $10 - its a little screwy but works well enough for certain thing.


  • work on it only with the engine cold
  • after you loosen each plug use something to blow the junk out of the plug wells
  • use boot/dialectric grease inside of the boots on both ends
  • use anti-seize on the plug threads
  • a piece of rubber hose on the end of a plug will let you thread it in with no chance of cross threading (I’ve always just used the lightest of touches but many people use this method).
  • learn about how to torque the plugs correctly - you don’t want to overtighten them. The strategies vary by design. Autozone’s online repair stuff might have a method you should use.

Ditto to oem spec plugs, side note for clarity “after you loosen each plug” not after you remove each plug, just in case. Great advice!

Use whatever the manual calls for. Its a Ford though so should use FOMOCO plugs not Mopar I believe.

Is your Ranger a 4 or a V6? Will make a big difference as to difficulty of plug replacement towards the back of the engine. Had a 97 4.0 and it was seriously hard to get out the rear plugs with the tools on hand.

Don’t bother checking old plug wires. Don’t buy the cheapest ones. Don’t buy Belden.

Use whatever the manual calls for. Its a Ford though so should use FOMOCO plugs not Mopar I believe.

Gee that was a dumb mistake…Mopar = Chryco…Fomoco plugs (or who-ever is the OEM supplier). I’ve been using NGK for years…I don’t keep up with the other brands anymore.

It is best to run OE plugs and wires. Parts store plugs may have the same temp, reach etc. but do not addresss the resistance of the plug. Your ignition was designed around certain parameters and it is best to stay within them. Same is true for wires.

Fancy plugs will toll nothing except ye walet.

Iridium plugs don’t break down when using Nitros. I doubt you are going to run nitros. Just buy the Ford recommended plug for the truck. If I don’t know when they were replaced, I replace the wires at the same time. You are already doing the plugs, so it takes no longer to do the wires. Peace of mind!