Terrible economy on Gen3 swap

[ergeorge]

Hi Folks,
I've swapped a 5.3L L59 flex fuel engine out of 2007 Silverado Classic into a 1993 Toyota Land Cruiser. Put a stage 1 Summit "Truck Cam" in it, and Hooker block hugger headers, but otherwise stock. No codes except an occasional P0300. Everything is present except for the fuel level sensor and the fuel composition sensor for the flex fuel stuff. Truck runs well - idle was rough so I bumped it about 50 rpm. I think I have the MAF dialed in pretty well according to the LTFT histogram. Haven't done anything else except turn off VATS, set the tire size (33") and rear end ratio (4.11) and turn off the flex fuel sensor and set the fuel composition sensor to "not fitted".

So, as I said, it's running well. But the fuel mileage is *terrible*. Like about 11-12 mpg around town, 15-16 hwy. Doesn't seem to matter much whether I baby it or beat on it. It's a 6000 pound full time 4WD truck, so I'm not expecting miracles. But other guys who've done this swap into these trucks are reporting 15-16 mpg around town and better hwy.

The primary reason I did this swap, instead of fixing the blown head gasket on the original I6, was to improve my range. I use the truck for back country off road trips and have been limited by how much fuel we can carry. But this is right back to where I started in that respect.

One immediate question - in the flex fuel section, there's a field labeled "Default Percentage" referring to the assumed alcohol % if the fuel composition sensor fails. This is set to 38%. It's 0 on stock tune files for non-flex trucks I've compared it to. Is this still used if I have the flex fuel control turned off? I'm going to load a tune with that set to 0 and see what happens.

Suggestions where to start/next steps? Brand new to this, so feeling my way along.
Thanks!

Here's the cam:
sum-8718_xl.jpg

And here's the latest tune & log. Maybe I should also note that this truck lives at about 7000 feet, and that's where the log was run.

[ergeorge]

Loaded the tune with the default percentage set to zero and zeroed the LTFT and took it out to run errands. Did a run up the highway & some stop & go in town driving similar to the previous log. LTFT fuel trim shifted negative by a few points, so it seems like that default percentage was maybe still doing something even with the flex stuff turned off. The butt dyno says the throttle response was a little better to.

[5FDP]

If the cruising rpm is above 2,000rpm, fuel mileage is going to go down.

To me that fuel mileage sounds right for how heavy the truck is and the full time four wheel drive. You gotta figure the big SUV's at the time from that era were rated at maybe 18mpg on the freeway and they even had a 2WD select on the transfer case.

[shtboxyj]

33s and 4.10s weighing 6k lbs sounds about right to me. hell ive never even seen double digits in my 02 2500 cclb. it weighs 6700lbs with 4.10 and 33s.

[ergeorge]

So I finally burned through enough of a tank to check the MPG with the "default percentage" fuel composition parameter set to 0. It came in at about 13.3mpg, so about a 15% bump relative to other checks for in town driving. Still not great, but a decent improvement.

[blindsquirrel]

I have an '06 Envoy LWB, 2 wheel drive, 31" street tires, 3.73 gear. It currently gets 10.9 MPG in-town, and that's an improvement of about .5 over what it was with the stock tune. I'd say you should be very very happy with numbers like yours with that combo.

[ergeorge]

I have an '06 Envoy LWB, 2 wheel drive, 31" street tires, 3.73 gear. It currently gets 10.9 MPG in-town, and that's an improvement of about .5 over what it was with the stock tune. I'd say you should be very very happy with numbers like yours with that combo.

Wow, that's crazy! Is it stock? EPA city shows about 14 mpg city (https://www.fueleconomy.gov/feg/bymo...mc_envoy.shtml) I've typically gotten a little better than EPA with a stock vehicle.

[blindsquirrel]

I've never had anything that beat EPA estimates. In 20-whatever years in dealerships there was probably once a week a customer with a new vehicle complaining that something must be wrong because it doesn't do what was claimed on the window sticker. Nothing was ever wrong with any of them.

[5FDP]

Driving habits is always the reason if you ask me.

I've owned my current truck for 15,000 miles, over that time the avg fuel mileage is 12.5mpg. I drive it 8-9 miles a day back and forth to work, gets 14 in the summer and like 8-9 in the winter because of remote starts. I can't reach the EPA avg because it's all short trips with minimal drive times, if I hit all green lights it's a 9 minute drive to work. I can beat the EPA estimates if I only do freeway, getting 22-23 on long trips isn't hard to do.

[Fast4.7]

If the cruising rpm is above 2,000rpm, fuel mileage is going to go down.

To me that fuel mileage sounds right for how heavy the truck is and the full time four wheel drive. You gotta figure the big SUV's at the time from that era were rated at maybe 18mpg on the freeway and they even had a 2WD select on the transfer case.

While full time 4x4 will hurt the MPG some compared to a 2wd lugging a cammed engine along at low rpm will hurt the MPG. I went from a 3.55 to a 4.56 in my Hemi Ram with a small cam and got better mileage. I went from a 3.73 to a 5.13 in my cammed L31 5.7 powered Express van and my city mileage increased 2 mpg yet even running 2,850 rpm @ 70 mph I got numerous tanks at 18 mpg. Lost about 1 mpg at 70 with nearly 800 rpm more. I run lean cruise and can run it pretty lean (~17:1) with about 48-52? of timing with the low cylinder loading at that rpm.