My wifes 2008 Eddie Bauer Explorer V-6 recently started having an erratic idle and we've started noticing it while at higher RPM's. Its almost as if there is a cylinder that misfires but no engine light is coming on. The car stumbles like it is going to start to die, then the idle jumps up and smooths out. A little while later it does the same thing. The car has I think 74,000 miles on it and has never had the plugs or wires changed. I change out the fuel filter roughly every 24,000 miles and did it recently in the spring.

Any places where I should start looking? Could a misfire not trigger the check engine light?

 

Yes, a misfire could be present and not trigger the CEL, especially if the misfire is somewhat erratic like you describe. There are multiple misfire monitors, and there need to be multiple consecutive misfires for the OBD-II system to set the CEL.

Some professional grade scan tools can get in to the PIDs and CIDs to look at individual cylinder misfire counts. I've even used this approach to identify individual cylinder misfires even before I realized I had a misfire.

So with the mileage and age on these plugs and wires I'd suggest starting with plugs and wires, although I'm a bit surprised your 2008 still has wires versus Coil on Plug (CoP) ignition. Maybe Ford adopted CoP on the V8 long before doing so on the V6. At a minimum replacing the plugs and wires would not be money wasted unless you plan to get rid of the Explorer soon.

-Rod

 

Rod,

I agree and was amazed that the 4.0 still had the rectangular 6 plug coil block / pack and still had the wires. My 05 F150 that had the 5.4 V-8 had the coil over plugs.

Like you said, the basic tune up stuff won't hurt the engine but I was under the impression that stuff was good for 100,000 miles now. While it isn't that far off , the age of the stuff could possibly be the factor.

I'll keep everyone updated as I plan on getting the parts and doing it either tomorrow or Sun.

 

From your description the spark plug wires would be one of the first things I'd replace if it were my truck. Yeah, the manufacturers like to claim 100k interval for the first scheduled maintenance, but from all the spark plug wires I've seen, I don't see where any plug wire technology has changed to warrant keeping the wires for 100k. The 100k interval probably has a bunch of fine print about the type of service the vehicle is used for and the climate it's used in.

-Rod