Spark Plug Gap

[Tactical Bacon]

I'm just a bit curious as to what everyone runs the gap at in their 4.0s. Last Wednesday when I was replacing the valve cover gasket (again) on my 91 I decided to check my spark plugs because it seemed like I was losing a bit of fuel economy. In my infinite wisdom, I got it in my head that they were supposed to be gapped at 0.060 instead of 0.035 (which I now remember verifying they were at when I put them in) and opened them up. Bad move you would think, right? Well, I can't notice that much of a difference. Cold start up actually seems faster now than before I opened up the gap. Not sure how the fuel mileage has changed since I did that midway through my current tank and I need to go fill up.

 

So, back to my curiosity. What gap does everyone else set their plugs at, and what brand and material plug do you run? I personally use the Champion RC12LYC and these have about 13000 miles on them over the past 3 years.

 

[fiatslug87]

I also use those Champions with a 0.035" gap.

[johnj92131]

The factory spec is 0.035 for the spark plug gap.

 

Over time, the gap will increase because the spark plug tip will erode away.  Eventually, your engine will start to misfire and run like crap - till you replace your plugs and properly gap them.  I just went thru this a few months back.  Replaced the plugs and the plug wires for the first time in 10 years.  Engine ran again like it should.

[Tactical Bacon]

The factory spec is 0.035 for the spark plug gap.

 

Over time, the gap will increase because the spark plug tip will erode away.  Eventually, your engine will start to misfire and run like crap - till you replace your plugs and properly gap them.  I just went thru this a few months back.  Replaced the plugs and the plug wires for the first time in 10 years.  Engine ran again like it should.

Preachin' to the choir.