Plug wires
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Freshman User
Joined: Oct 2014
Posts: 26
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Plug wires
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 !!
Lead Driver
Joined: Mar 2013
Posts: 7,460
Likes: 85
From: Kent Station, WA
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.
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.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
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 !!
Logistics Pro
Joined: Jan 2011
Posts: 4,890
Likes: 3,442
From: Ohio
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.
Change the PCV valve, it's cheap and easy.
X2 on the MAF sensor and air filter.
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Lead Driver
Joined: Nov 2012
Posts: 8,304
Likes: 28
From: Salem, VA
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.
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.
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Posting Guru
Joined: Jun 2004
Posts: 2,433
Likes: 1
From: Apex, N.C.
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.
More Turbo
Joined: Apr 2014
Posts: 645
Likes: 29
From: Toronto, Canada
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.
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.
Junior User
Joined: Oct 2014
Posts: 96
Likes: 1
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.
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.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
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.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
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.
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.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
Probably due to driving change, locked in 4wd etc.
Junior User
Joined: Oct 2014
Posts: 96
Likes: 1
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!