Thought I'd start a new thread on this since the other one was getting pretty long.

Here is the previous thread for reference:

https://landroverforums.com/forum/di...problem-83329/

So I just completed a trip from WV to GA (800 or so miles). Here are my findings (for purposes of the thread we will assume miles per hour was between 60 and 70 (generally 65), I drive like I have an egg on the gas and brake pedals. Outside of a few hill climbs RPMs stayed around 2200-2500. It only pegged 4000 rpm once, and if it did downshift it was at 3000 or so rpms.

All fillups were with EXXON Supreme 93 octane. I started with a full tank and a bottle of Techron fuel system cleaner.

1st Leg: 213.6 miles until fill up. Took 18 gallons. Put in another bottle of Techron. LTFT was at 3.1%

MPG = 11.86

2d Leg: 234.9 miles until fill up. Took 19.5 gallons. No additives this time. LTFT was still 3.1%

MPG = 12.04

3rd Leg: 235 miles until fill up. 18.7 gallons. (roughly half of this leg was with LTFT of 3.1. About 40 miles were in town, but not really stop and go. LTFT dropped at one point to 2.3. This morning when I started back home LTFT was at 6.3)

MPG = 12.5 However, LTFT 3.1 for half a tank, then 6.3 for half a tank.

Here I put in a bottle of that Berryman Chemtool fuel system cleaner instead of Techron.

Here is where it gets interesting. I had noticed that over the entire trip I could get 100 miles with the fuel showing 3/4 tank full. At about half a tank I'm around 150-160 miles. Empty (or darn near the light coming on) I'm at the 235 or so indicated above. So my truck was getting 100 miles on a quarter tank. After that (between 3/4 and 0) it goes an additional 135 miles.

I'm thinking it's just a gauge problem, but this time I stop and test my theory.

Leg 4. 106.1 miles. Stop at exactly 1/4 tank to fill up. It takes only 6.6 gallons. LTFT is still 6.3

MPG = 16.07 miles per gallon!!!

I continue driving. LTFT stays at 6.3. At 3/4 tank again I note I am at 102 miles into the drive. I don't stop because I want to see if maybe overall mpg has improved, or if there really is something going on between 1/4 and 0 tank.

Leg 5. 213 miles. 15 gallons. (tank is now between 1/2 and 1/4 tank)

14.2 MPG.

Which leads me to believe....hell I don't know. If I fill up at 3/4 tank I'm pulling 16 miles per gallon. If I go down to between 1/2 and 1/4 tank I'm at 14.2. If I go until just about the time the light goes on I drop to 12 mpg.

So what would cause this? All the driving was the same. All highway miles. Same route there and back.

 

I hate to ask but did you happen to record the STFT too during this time......?

 

STFT was fluctuating as normal, every second or so. Up to 14 a couple times when under big load, but also at -2, -3, 0.0, up to 2, 3, 4, down to 0, etc....which is, as I understand it, how it should be as it's constantly compensating.

The weird thing was how LTFT was 3.1 the entire way down. Didn't fluctuate at all. Then it briefly hit 2.3 after a couple jogs around town. Then this morning I started it up and it went to 6.3 and stayed there 400 miles.

 

Yeah, it is weird and my pea brain is mush. A clogging injector will raise the LTFT and so can a MAF underreporting air mass. It's not over 10% though so whatever it is its smallish. Have you by any chance looked at the vacuum lines around the filler valve or the tank to the canister? Just wondering because a post just brought up an air leak on the evap line.

Your motor is running lean and the LTFT numbers are positive meaning the ECM is adding fuel, not much but that's where the numbers are. Do you have a tool to clear the adaptive values with? The STFT is stored as is the LTFT.

 

Yeah on the other site someone said it was running lean, but it has been smoke tested, no vacuum leaks showed. No codes show.

But I had worse mpg at higher LTFT. At 6.3 it was slightly better overall and significantly better (+4mpg) at 3/4 to full. That is what I can't figure out.

 

Yeah I've been mulling that over too because I noticed it with mine, I never went below 290 miles a tank on long trips though. I attributed the gauge needle hovering high due to overfilling.

 

Yeah if it was the gauge my mpg would be the same and I would have used a corresponding level of fuel. But 16 mpg is a huge increase.

I'm wondering if less than 3/4 full affects the fuel pressure somehow?

 

To throw another monkey onto the pile:


Morning's drive. Closed Loop. 10 minutes. Every STFT was negative (indicating it's running rich and trying to compensate). Fluctuating between a very brief 0 to up to -13 on both banks. Constantly fluctuating, but negative.


LTFT did not move whatsoever. Stayed 6.3 for 10 minutes.


This was an early morning drive, so that's worth considering, too. But still.....

 

Drive home: 15 mins stop and go. 2 miles total. STFT completely negative numbers the entire 15 minutes. LTFT stayed 6.3

 

Tested fuel pressure:

key on 38
running 30
2500 rpms 25

clamp return line: over 100 psi

vavuum to regulator removed: 38 psi

20 mins engine off: 20 psi
1.5 hours engine off: 0 psi