34MPG in a 2002 Grand Cherokee diesel

[bandit86]

My son has a ml350 bluetec, consistently gets high 7s. My dad's GC diesel lucky to stay in 11s. Same engine, different transmission and I guess the ml is a bit more aerodynamic. Bigger tires helped the jeep by cutting engine rpm

[AdrianD]

What year ML and wear year GC?
That will make a big difference.

I've never had the chance to reach the same mileage with the 2004 Jeep, probably because of the nice summer tires I had on the 2002, the allseasons on the 2004 might bring some fuel consumption penalty.

Recently I've experimented with fuel pressure increase in the engine tune and my recent tank showed some improvement:
Average fuel consumption over 55.000km is 10.267L/100km (22.91 mpg), and with the recent update I used an entire tank of fuel in varied conditions, including offroading in low range, city driving and managed 9.66L/100km (24.31 mpg).
The fuel pressure increase should help fuel atomization, decrease injection time and slightly advance timing, all should help fuel consumption.

Another update since the last activity was tuning the transmission control unit to lock the torque converter earlier, at 57km/h instead of 70km/h from the factory. This allows me to drive with the converter locked when passing through small towns on national roads, bringing some small improvement in fuel consumption.

[cRiPpLe_rOoStEr]

3rd-gen or 4th-gen ML?

[AdrianD]

One more recent update, a DIY 2.75" cat-back exhaust, with a straight through muffler and dumped before the rear axle, so that it doesn't have to snake over the axle. Factory exhaust went down from 2.5" to 2.25" in the flexible section, now it's at 2.75" all the way to the back.

Trip computer showed at least 0.2L/100km drop on a trip I do a lot, the transmission is more "eager" to shift into 5th before 70km/h and I can now accelerate from under 60km/h in 5th gear.

I still need to test the actual manifold pressure at 110km/h cruising speed, in the past it was 1240mbar, curious to see if it dropped a bit and then install an O2 sensor to check fine-tune the A/F ratio. The actual injected quantity was at times on the last trip under 15mg/stroke, below the threshold where I increased the fuel rail pressure, so I need to update that too.

Next on the list is a more modern turbo, which should also help VE because of freer flowing exhaust housing. Not installing it for the economy gains, but for the 200kw power target

[cRiPpLe_rOoStEr]

Once in a while, some performance improvement may also provide a better fuel-efficiency...