fuel mileage question

Joe Romas · **Posted:** Sun Nov 09, 2008 10:05 am

KJ79.

Your mileage is about the worst I've ever gotten. Last tank of all around town short trips was 23.6 mpg hand calculated and I'm happy with that. My problem like I think is yours, is highway mileage, best ever and only once was 25 mpg. Looking at your specs I wonder if your tires and lift have anything to do with your poor highway showing??

Joe

Hjalti · **Posted:** Sun Nov 09, 2008 1:28 pm

Update from N-Iceland, I am referring to US-gallons (the converter is here: http://www.tdiclub.com/misc/conversions.html). The maintenance is more or less according to the book and there are not much differences after fresh oil and filters. I have not done any mechanical changes and cleaning the MAP sensor does not change much, the thing failed a few weeks back but the new one delivers same economy. Things could though be worse since my father in law was doing 9 mpg on a 4.0 litre XJ while my KJ was doing 14 mpg!

aandlwoods · **Joined:** Mon Jun 09, 2008 4:53 pm **Posts:** 96

35 mpg on the highway doing 65 with no wind and level road on regular ULSD. I credit SEGR and the spdiesel module.

jbees · **Joined:** Thu Dec 07, 2006 2:45 pm **Posts:** 20

I'm getting over 19 around town and 26+ on a recent road trip. Got the INMotion econo tune, unpluged MAP, fairly new MAS. Don't know why but with recent oil change I picked up 1 MPG using 15/40 Amsoil and their filter and was using syn oil before. Also changed the venting so I now mark my spot with a bit of oil. Keeps the Harleys feeling their amounst friends. I'm trying to find a 3" turbo back exhaust for it now.

KJ79 · **Posted:** Mon Nov 10, 2008 4:38 pm

I used to get 26 mpg, so I lost about 10. That was with my modest lift and 235/75 tires. I have tried the ORM and could not detect any improvement neither in performance nor mileage. I have the SEGR kit sitting in the drawer, but since the ORM did not improve anything for me, I don't expect the SEGR to change that. Besides I am still under warranty. The brakes are not dragging. Turbo seems fine, after my last dealer, (they tigthened some clamps), I seem to be getting less diesel smell in the cabin and less black smoke. On the freeway it needs only a touch of gas (maybe 1/16") to maintain 65 mph. Exhaust seems to have normal flow now, used to be lo flow (because of loose clamps?!? My neighbours Durango (it's got a hemi) burns less gas than I burn diesel. I have never changed the tiny transparent filter behind the air filter - would that have any impact?
Yes I use u.s. gallons and "hand calculate"the mileage.
-Starting to wonder now, do I need a locking fuel cap?

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

Jbees, fresh oil amost always gives a bump in mpg. Will drop back down as the oil ages.

HJ79, black smoke is not normal for these vehicles. The only smoke mine ever emits is a little puff when it first cranks up on a cold morning, or a slightly darker puff when I stomp it to accelerate onto a freeway. This is with the SEGR and a tuning box.

If the ORM made no difference to your mpg, are you getting any error codes? ORM improved my mpg substantially, and I could tell a significant difference power wise. Could be your EGR is hanging already?

Black smoke generally speaks to clogged fuel filter, clogged air filter, or clogged MAP sensor. Cleaning the MAP and checking the air filter would be top of my list where I you. If none of those fix it, next likely culprits may be leaky turbo hoses or air getting into the fuel system through leaks at the filter head or elsewhere.

The little clear boost filter isn't like to be giving a problem.

I'm puzzled by the diesel smell in the cabin. I've never had this and it doesn't sound good. Smell like diesel fuel, or diesel exhaust?

KJ79 · **Posted:** Tue Nov 11, 2008 2:21 am

Thanks Threeweight

Puzzled by the diesel smell in the cabin? This is actually somewhat resolved since the dealer found a loose clamp or clamps on the EGR. I don't get it in the cabin anymore, unless I have all the windows open and I'm not moving. It is a bit too cold for that now anyhow. Exhaust smells like foul smelling very sooty diesel exhaust.

Getting zero error codes, no CEL and checked with a code reader to make sure of that. EGR was replaced in September, did make zero difference.

MAP sensor is clean(ed), I replaced fuel and air filter was replaced, don't seem to have leaky turbo hoses as I have no loss of power, spools up quickly and no hissing noises anymore (after last dealer visit), checked filterhead several times for air and bled a tiny bit of air out. Plunger pump was fairly firm to begin with. A year ago I had tons of air in it, severe bucking and so on, but this is solved.

fuel mileage question

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