I have a 98 Expedition with a 5.4/95k miles. After reading several posts I'm leaning towards a plug/C.O.P. problem but can't rule out the O2 sensor. Any thoughts from the PRO's? Thanks in advance!

 

You're barking up the wrong tree.

You've got a vacuum leak. The PCV hose elbow on the rear of the TB is the most common location.

It's certainly not an ignition problem nor is it an O2 sensor problem.

Steve

 

Steve's Right, 171 basically means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

174 means the same thing except your oxygen sensor in bank 2 detected a lean condition . Bank 2 is generally the side of the engine that doesn't have cylinder #1.

So , your 02 sensors are working as they should be.

In the vast majority of cases, simply cleaning the MAF sensor does the trick. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling. I use compressed air BUT govern it - dial it way down (10lb's or so)

Inspect all vacuum and PCV hoses, replace if necessary. This is very common as well, I'm betting this is your problem as Steve suggests, you received both codes in tandem. Check this out first.

Check for a dirty fuel filter and proper fuel pressure if the above do not work.

It's possible that it could be your manifold gaskets as well , but I seriously doubt that.

Good Luck !!!

 

Thanks guys. I'll check that out and let you know. I've already ordered the coils and plugs from the ebay link so I might as well change those out while I'm in there...Thanks for the link!

Butch