Sudden loss of MPG

c7train · 12-14-2015, 01:57 PM

I have a 2007 E350 V10 with 109k on the clock. We got it with 48k miles and was getting over 12mpg all the time, maybe 13-14 (better at sea-level). This last trip I got 9mpg. Has anyone experienced anything like this?

Both valve covers have oil on them so I checked the PCV valve idea, but it rattles just fine like it should, although it doesn't seem to seal all that well to the valve cover. The passenger side valve cover has what appears to be the "heated" PCV valve while the driver's side just appears to have either a regular PCV valve or just a grommet and hose coming out of it. Ideas here?

Also, I have the little puff of smoke on start up but it's very random and hardly ever happens. Thoughts on this? The van runs great and doesn't seem to use any oil. No check engine lights are on either, I have it chipped from 5 star tuning, would that effect check engine light not coming on?

Any help on this would be much appreciated, we are heading out on a trip for The rest of December and start of January and It would be nice to get the "regular" MPG again.

carringb · 12-15-2015, 03:12 AM

Have you changed the plugs yet? You're past due, and when they get worn enough mileage tanks. For me it happened first at 115,000 miles.

As for the puff of smoke.... It's the valve guides. Switching to good synthetic will restore the seals. Mine did the same when I first bought it. By 150,000 miles that went away completely.

BajaSportsmobile · 12-15-2015, 09:15 AM

Is it down on power as well?

c7train · 12-16-2015, 09:00 AM

Carringb, I haven't gotten up the guts to change the plugs yet, maybe that's the next step. I've had the dog house off twice now and the new plugs in hand, but wimped out both times. Soon, soon.

Agile, it doesn't feel as though it is down on power. I can pull the same hills at the same speeds like usual.

I'll keep you both posted on my findings, thanks for replying it's so helpful to have a group of people willing to provide constructive info.
C.

carringb · 12-16-2015, 05:16 PM

Yeah do the plugs. And new boots. Make sure you use oem or equivalent AutoLite double platinums. Copper plugs will burn up fast in a v10.

MadScience · 12-16-2015, 10:13 PM

While I'd take CarringB's advice over my own, here are some _additional_ thoughts:

Simple/dumb thing to check is always tire pressure. That and working my engine oil too long/hard has resulted in similar drops for me. A couple 1k changes fixed the latter, but really it was nasty sludgy looking oil that drove me to that.

(Well, and towing a heavy or non-aero-dynamic trailer, but you'd be down on power if you somehow managed to not notice that in any other way

).

Obviously, 4-low on trails burns fuel at a truly impressive rate.

(my experience is on a 99 v10 on 33.5" tires)

carringb · 12-17-2015, 08:55 PM

Tire pressure is a good thing to check anyways

There's dozens of items that can cause poor fuel economy. But worn spark plugs will cause it, so its best to always make sure maintenance is up to date whenever trying to diagnose a problem.

On the tire pressure note.... A couple years ago mine fuel economy tanked. Like 6 MPG bad when towing. I couldn't figure it out, and didn't think it was my plugs yet. Finally on a whim a decided to check my tires. One of the rear inside duals had ZERO psi! The rim was cracked!. My fuel economy was terrible for over 1,000 miles before I finally found the bum tire. Even with that, I no handling problems whatsoever.