Drastic reduction in MPG

degride

degride

Well-known member
Sep 22, 2008
67
1
Somewhere on Earth
Since we are all LR owners we accept the MPG facts as dismal as they are That being said, dropping from my typical 12-13 MPG around town down to a new low this weekend at 8.8 leads me to post this and seek out some solutions.

I started noticing the drop back in October when I decided to keep the truck (an 03) and drop in a locking t-case along with a D1 shifter. I resealed the t-case but nothing else. I noticed the output flanges rotated somewhat "tighter" with the new t-case than the t-case that came out of the truck. But didn't think too much about it. The reason I don't think it's the t-case is because the MPG has been fluctuating from the ridiculousness of 8.8 to low 11s. I also don't think it's the winter blend of gas. It might contribute but it's never been this drastic.

What I have done since then to try and rule out anything is:

new plugs (needed it anyway)
new wires (needed it anyway)

I'm going to do the following next:

swap fluids in fr/rr diffs (needs it)
replace MAF (needs it as it still has original with 217k on the clock)
replace fuel fitler (can't hurt since it has the original in it)
swap transmission fluid (can't hurt)

I don't believe the brakes are dragging. I'm not sure how to test if the parking brake is placing a drag on the drive-train.

Anyone have any other potential solutions to track down? It's not throwing any codes and considering the truck gets used and abused like a proper Land Rover should it's in remarkable shape but I'm starting to get pissed at it now.
 
the deputy

the deputy

Well-known member
Sep 20, 2017
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michigan
To bad you hadn't checked compression while you had the plugs out. Might be getting just plan tired. Especially, when combined with the winter blend.

Brian.
 
degride

degride

Well-known member
Sep 22, 2008
67
1
Somewhere on Earth
I had thought of that...but given the mountains I drive through (moved to the rockies) it still has plenty of pep for a 4.6 w/217HP coupled with the mileage.

But I'll add that to the list just to rule it out.

Here is the interesting thing, and it could be a huge coincidence, this all started the first time engaged the CDL. I've had no problems with it locking or unlocking but, going back through the app that I track my mileage/fuel consumption with it all started the same time.

Again, could be one of those Rover coincidences but given our propensity for self-infliction, it doesn't warrant someone either agreeing or telling me I've officially become a Rover hypochondriac. :rofl: :eek:

How would one go about testing if the muffler or cats have partially collapsed and causing this?
 
R

robertf

Well-known member
Jan 22, 2006
4,796
364
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D2 is returnless, so is it possible that the fuel pump regulator is malfunctioning?

How is the idle? Oil cap and dipstick tight so that all air is metered through the MAF? Any of the plastic emissions line cracked?
 
WaltNYC

WaltNYC

Well-known member
Mar 3, 2010
710
138
NYC
I'd want to see the fuel trims also. Do you have a live data reader? Torq or OBD Fusion or something of the sort? Look for STFT and LTFT on each bank. If not, I recommend it. Best $25 you'll spend on your truck.
 
squirt

squirt

Well-known member
Nov 13, 2008
824
13
Los Angeles
p m said:
That requires a vacuum gauge visible from the driver's seat and feet on both pedals.
Click to expand...

You can also tee a pressure gauge off the front O2 sensors... or for a very quick and dirty method, just pull the front O2's. It will be ridiculously loud, but if you see a big performance increase your exhaust is blocked.
 
degride

degride

Well-known member
Sep 22, 2008
67
1
Somewhere on Earth
All the O2 sensors have been replaced with new ones within the last 10k miles. No rough idle, all plastic vacuum lines are in good shape.

Even though the D2 doesn't have a filter per se it is a part of the pump itself. I've always used premium in it since day one. When I did the heads on it about 40k ago not an ounce of sludge inside (this really surprised me).

I'm gonna go grab a vacuum gauge today and run some tests and see what I get back. I do not have a real-time code reader; only ODBII reader to clear any codes which are few and far between. Guess I'll be visiting Amazon today.

One thing I did notice this morning, got in the car from the store and the fuel gauge was right below the upper mark. Drove three miles home, turned it off, then switched it back on, and gauge had dropped just above the middle point between the 3/4 mark and the full mark. Weird.
 
coop74

coop74

Well-known member
Dec 10, 2015
287
7
Alcoa TN
you might also want to check tire pressures... with extreme cold they could be very low causing extra drag...
 
degride

degride

Well-known member
Sep 22, 2008
67
1
Somewhere on Earth
Yeah winter blend does equate to loss of MPG but I've never seen it this bad. Typically it drops to around 11-11.5 for me.

We drove to Baja last spring and that trip averaged around 13.5 (32.5 tires, bar up front, lift, full roof rack, loaded down, etc.). This time however, driving around town and over passes every weekend is out of the ordinary.

I'm getting around 14" on the vacuum gauge which given the altitude I live at (around 5500 ft) is about average. I guess I could inflate my tires to around 40 on each corner. I typically run 36 up front 40 in the rear but I don't think this will make much of a difference.

Can anyone confirm vacuum readings?
 
coop74

coop74

Well-known member
Dec 10, 2015
287
7
Alcoa TN
degride said:
Yeah winter blend does equate to loss of MPG but I've never seen it this bad. Typically it drops to around 11-11.5 for me.

We drove to Baja last spring and that trip averaged around 13.5 (32.5 tires, bar up front, lift, full roof rack, loaded down, etc.). This time however, driving around town and over passes every weekend is out of the ordinary.

I'm getting around 14" on the vacuum gauge which given the altitude I live at (around 5500 ft) is about average. I guess I could inflate my tires to around 40 on each corner. I typically run 36 up front 40 in the rear but I don't think this will make much of a difference.

Can anyone confirm vacuum readings?
Click to expand...

I am not saying over inflate your tires just know that the pressure in the tire at 70 degrees will lower by a lot when the ambient temperature is in the 20's.
 
p m

p m

Administrator
Staff member
Apr 19, 2004
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La Jolla, CA
www.3rj.org
degride said:
I'm getting around 14" on the vacuum gauge which given the altitude I live at (around 5500 ft) is about average.
Click to expand...
You need not idle-in-neutral vacuum readings, but rather vacuum reading in case when your parking brake is applied, your left foot it on brake pedal hard, and your right foot is on gas trying to get close to torque converter stall speed. If you see vacuum dropping considerably close to 2k rpm, you may have restriction in your catalytic converters (or downstream of them).

I doubt it is your problem, though. I had a Classic with broken and plugged cats, and it practically wouldn't run beyond 2500 rpm under load - but the gas mileage remained about the same.

Depending how cold it is and what oil you have in the diffs and transfer case - it alone can account for this much of a drop. The differentials can easily account for 10% of all energy losses, and that - fully warmed up.
 
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