I recently had the larger DPFE Tube fail just below the sensor (Truck has 252,000 miles). I replaced both tubes buying that package from rock auto that contains lengths of both sizes needed in silicone. The engine code went away, but it seems like the drop I saw in fuel mileage hasn't recovered back to what it should be, so maybe the DPFE Tube was just a coincidence and the truck has some other issue. I drove the truck 500-600 miles since the new tubes. Do you think a relearn would take longer than that? I don't, so what other non-code items have people found to be suspect in a sudden drop in fuel mileage other than winter gas (I don't think we've switched to winter gas yet, but that is the mileage I am seeing: 260-ish per tank rather than 360-ish), air filter (checked), fuel leak (relatively new tank, and no leaks) and tire pressures (only other thing checked so far).

I poked around on here and dirty MAF sounds maybe like a possibility, so perhaps I'll try cleaning that. Any other suggestions? Again, no code currently, and 252,000 miles.

Thanks for any suggestions,
Cooter

 

Don't mean to throw out a worst case scenario first, but I had this happen on a '94 Ranger I used to have. The bottom half of one of the DPFE hoses had just flat out disappeared and it smelled gassy, too. Replaced and it happened again. Since that 2.3L ended up with zero compression on cylinder #4, in retrospect, I bet some unburned fuel in the exhaust was burning up that hose over a short bit of time and it did in two cat converters over two years, too. That engine got to about 284k miles before it got the diagnosis.

No need for any "relearn", but I certainly would get a compression test done. Granted, I would expect a misfire code with OBD2 being as precise as it is, but you never know. It takes a few bad coils to even get a misfire when those are going bad. Certainly having to punch the pedal a bit more because at least one cylinder isn't carrying its load could knock your MPGs down.

 

How many miles on what brand spark plugs? Have you tried cleaning the throttle body?

Up north, the winter gas switchover is usually October 1.

 

Cats are factory on my truck. I suspected a cat (or two) earlier this summer as the truck felt to have a mid-range lull or dead spot like it was down on power. However, whatever that was is gone as the truck seems to pull just fine now. Plugs only have a little over 30K on them and are Motorcraft. I don't think I want to pull the plugs again...even if just for a compression check, so I am going to explore the other items first.

I'll scope the throttle body when looking into the maf situation although I don't think the throttle body would cause a drop off in fuel mileage.

Thanks for the suggestions. Keep them coming.

 

Oh, and regards to the Winter Gas. The code for the DPFE happened back in late August and that was around when I first noticed the mileage issue. The truck more or less sat for a couple weeks, then I fixed it, and then I started driving it again just a couple weeks ago, so perhaps whatever the issue was back then was fixed, but it took several miles for the computer to relearn. And then I found winter gas....so perhaps a coincidence is in here somewhere after all.