When my 2000 ford excursion was in the shop a while back the mechanic told us not to change the plugs/ plug wires until we start running rough or they go bad... Has anybody heard this? Lately I've been getting worse milage than normal. City driving I normally get 9-10 lately I've had 7-8. Could it be my plugs? Or should I try the air filter first? Any ideas are helpful and welcome !!

 

What engine and mileage do you have?

Check the air filter regardless of engine if dirty it will rob performance and mileage. Clean the MAF, change the fuel filter run some techron or seafoam through the gas tank.

 

Get a new mechanic. They start going bad the day you put them in.............like tires.

 

You sure that's not a myth too?

 

thanks man and we got a v10 and about 182k miles.

 

yep..............

 

Do you know if the plugs were ever changed since new?

Change the PCV valve, it's cheap and easy.

X2 on the MAF sensor and air filter.

 

Mechanic sounds like an idiot, but then again you sound smart enough to question him and ask us on here so it doesn't matter Personally I would go with the cheapest/easiest things first. Basically everything that has been said thus far:

PCV valve
clean MAF
Air filter
Depending on mileage/length of ownership/quality of gasoline in your area the fuel filter
And the seafoam while expensive does work. I have yet to use it on my X but I have on most of my other vehicles over the years.

 

My neighbor just changed his last Friday for the first time ever since he bought his F-350 in 2003. I was shocked at how good they looked with 170,000 miles on them. Some of the boots were in pretty rough shape though.I was too lazy to walk back to my house and get the camera or the phone to take pics. Now I wish I had. I will call in the morning and see if he still has them.

 

Do you live anywhere it gets cold?

If so your lower MPG might be due to the winter additives they put in the gas.

Here in Canada we all get lower MPG in the winter and come summer time magically those 1-2 MPG are back.

 

Change the plugs/boots and likely you have at least one coil going bad.

The hard thing on a coil on plug engine is finding bad coils as none of the ODBII software tracks coils specifically. On a V10 they run so smooth with so many cylinders than one or two missing is hard to notice. A code won't get thrown until a coil totally malfunctions btw. Replacing all the coils with Motorcraft OEM is about $500 if you DIY, don't go for the cheaper Accel sets as they don't have longevity.

I'm trying to track down a bad coil on my engine as I've noticed a bad drop in MPG and intermittent misfire at road speeds under light load. It's masked when I drop out of OD as the RPM increases due to so many cylinders firing. I too thought it was just plugs and changed them at about 190K (the gap had increased and the edges of the electrode were rounded but otherwise they were fine.)

If you've got the money just replace the whole set of coils along with the plugs & boots because eventually more coils will be going out.

 

That would be interesting. While plugs will fire longer than yesteryear they still go downhill from day one (like anything with a lifespan) and HP and MPG's go down slowly without you noticing it.

 

That's a bad idea because they go out one at a time if at all. Many trucks in here have 200k miles on them with original coils and finding the bad one is easy. Boots are the biggest culprit of a miss also.

 

Probably due to driving change, locked in 4wd etc.

 

Note he's got 170k... I'm nearly at 200K. I have read numerous posts of guys with faulty coils at less than half either of our mileage. And note I said if he's got the money he could replace them all, not that it was necessity.

Finding a bad one is not easy on a V10. Easy is putting a oscilloscope pick-up on a coil and a pick-up on a spark plug wire and running at load, the way we use to do it before all the electronics. Can't do the same now as there are 10 separate coils with 10 separate signals not regularly monitored by the computer.

BTW, when I removed the plugs/boots/coils at 190K I found no appreciable wear/tear on the components in question (they had never been off the engine in 10years 190K). I suspect the culprit in boot damage is more related to people tearing component parts apart, ie, swapping coils around trying to find a faulty one!