I have ownedmy wife's 98 navigator since 2000. It now has 115K and runs good. It has had normal maint. no major repairs. But in the last 5 - 6K it seems down on power. No CEK, mileage is a little down, not much, just down on power. It is really noticeable w/ the AC on. I have cleaned the TB, changed plugs @ 100K, 3" magnaflow system other than that stock 4wd Nav.
Any suggestions?

 

this is a long shot but perhaps the cat. is going bad. i had a friend who had one go bad and it had a loss in power that got worse until it wouldnt run i mean it would idle but thats it. from what i understand if for some reason your cat. overheats it can melt the ctalytic media and clog it up and cause a loss in power. but someone else might have a better idea.

 

i would bet its the cat or cats i had that hapen on my 93 was afraid to get on the high way i lost so much power after i replaced them it ran like a new truck

 

Thanks. I would not have thought about the exhaust system, but it more than makes sense. I will go have them checked. They did it three years ago when I have the system installed. They used a heat sensor gun to check the difference in temps between different sides of the cats. It was marginal then, so I am sure that is it.
Again Thanks

 

Fuel filter maybe ? Have you ever changed it ?