looking for a couple m.p.g gains.

[smslyguy]

I have a completely stock 2000 gmc with a 01 c.o.s. and i average about 14.5 m.p.g. I am looking for anything to help me for a few extra m.p.g. I have turned off cat protection, and tried bumping the timming 15% at cruising speed, but not much luck with any of these. Any suggestions????

the truck as 120,000 miles and is tuned up as well.

[LBZoom]

I have heard some mention of changing the 02 switch points...but i'm not really a gas engine tuner, more diesel. But a buddy of mine has a 99 chevy with the 5.3, ext. cab short bed and get's closer to 18-19hwy.


On his truck we simply adjusted timing across much of the table, and increased the Main VE table to some extent. Our main goal was power production but in the process we managed to enhance the efficiency some as well so it was a win-win for us. I can give you the tune if you'd like to see how I did things. Just PM me

[smslyguy]

I have heard some mention of changing the 02 switch points...but i'm not really a gas engine tuner, more diesel. But a buddy of mine has a 99 chevy with the 5.3, ext. cab short bed and get's closer to 18-19hwy.


On his truck we simply adjusted timing across much of the table, and increased the Main VE table to some extent. Our main goal was power production but in the process we managed to enhance the efficiency some as well so it was a win-win for us. I can give you the tune if you'd like to see how I did things. Just PM me

yes could you plese? that would be a huge saver for me and i would greatly appreciate that.

I have tried adjusting the switch points with not much luck, but if i had a tune like your buddy's it would deffently be a great start.

[whackem04]

if you change AFR to say 15.02 would this help in mileage and have the PE take care of the power?

[GAMEOVER]

I have my AFR set to 15.6-15.9:1 on the highway and I get pretty good gas mileage. I just have to flash in my Highway tune and keep an eye on the WBO2...:D
I actually get better gas mileage with AFM or 4 Cylinder mode shut-off

[smslyguy]

if you change AFR to say 15.02 would this help in mileage and have the PE take care of the power?

Ya i have ran 15.52 a.f.r as well and did notice a little gain, but didn't run it that long cause i didn't have a w.b.

[Mr. P.]

I had a very happy economy result this last time out driving the truck - 2003 Silverado SS AWD with shorter tires (30") and turning a Paxton blower, my average combined mileage before installing the Paxton was high 13's; last night I drove 1-hr from Plano through Dallas to Arlington, heavy freeway rush hour traffic 45-80 mph and lots of left-lane squatters and cussing and road rage. When I looked at the DIC I had averaged 15.9 WOO-HOO!!! At 65-mph (2100-rpm) the mileage was 17. The truck has never had that kind of economy even when brand new box stock. I am running COS3 OLSD with DFCO and PE disabled, the VE table is nailed up to 2800-RPM +- 1.25% error, and my commanded EQR in "cruise" cells is .92 and .95. My advice is to log the truck on a combined city/hwy daily-driven commuter trip, and use the BEN MAP counts to determine which cells get "driven in" the most, make your AFR 16:1 in those cells (EQR = .92), and in the VE table cells immediately surrounding those set AFR to 15.5:1. Verify the AFR with either road or dyno logging on the STOCK timing curve, the truck timing curve is very tame and did not detonate on my truck even with the blower, and once you have the AFR behaving like you want then go ahead and map out MBT optimized timing using a dyno and TA-DA you're in business! On my truck (5500-lbs) I found that even on the freeway it is not uncommon to be in the 70kpa area of the VE table, so don't richen the AFR until 75kpa and then ramp in your fuel until you have 12.2:1 to 12.4:1 at WOT.

Mr. P. :)

One other thing - the tune I describe in my truck now is not 'lame' at all, the truck runs like a f'n animal, very crisp and IMO is the best it has ever run. Also, in AFR tuning minute changes matter, my main VE table was +- 3-4% error on the wideband and I was getting 12-13 MPG, this last time I now have that error between 0.75 and 1.5% margin, many of the cells in fact changed less than 1/2% one way or the other) and the economy instantly jumped to high 15s. And in my experience, using the process outlined in the AutoVE tutorial you will have to drive the vehicle weeks until the VE table 'settles in' mathematically to that degree of precision (due to wideband delay and the problem of interpolation between cells) - there is a better way, you have to sit down and really examine the logs and make a spreadsheet of your own BEN corrections. You also have to offset (advance) the wideband data feed one frame to better line up with the commanded AFR IMO.

My $0.02.

[Mr. P.]

ONE OTHER VERY IMPORTANT THING -

3 weekends ago, helped a friend with his 2003 Silverado SS AWD with about the same mileage as the OP's truck (115K-miles) and got surprising result:

He had a cam installed this last summer, and being broke did not have the money to install a new timing chain; at that time he installed the cam & springs & push rods, the motor ran pretty strong and was mail-order tuned with EFILive by Justin Gadberry and that truck had an average high-13's MPG economy since, and my friend was fine with that as it was "a heavy-ass truck with a cam" and most get about that level of economy (13.5 - 14.0 MPG).

Fast forward to 3-weeks ago: my friend had $100 and we bought a stock LS2 timing chain and cam sprocket, tore the front of the motor apart and replace the original 115K-mile timing set pieces. Now I knew the original timing chain had stretched, they all do, but the reason that we replaced the chain was for the improved strength of the LS2 chain. The surprise was that after we had the motor together the idle vacuum improved 2-inches (!) the truck ran remarkably better at idle -and- off-idle -and- cruise, and the average combined mileage instantly shot from mid-13s to mid-15s. No lie, no joke, no exaggeration. I was stunned, I had no idea cam timing being off a few degrees would have that drastic an effect on economy; this might also be a case where the factory cam is more tolerant of a slack chain and not loose as much economy as a retarded aftermarket cam, but still if I hadn't seen it with my own eyes I would have thought it an exaggeration - 2.0 MPG improvement with a $100 outlay in parts.

After seeing this, makes me weep for the mod motor guys and their 6-feet in timing chains!

Mr. P. :)

[joecar]

Yes, the cam should be where it belongs, inside the block, a short distance above the crank... :cucumber:

[Chevy366]

My advice is to log the truck on a combined city/hwy daily-driven commuter trip, and use the BEN MAP counts to determine which cells get "driven in" the most, make your AFR 16:1 in those cells (EQR = .92), and in the VE table cells immediately surrounding those set AFR to 15.5:1.

Mr. P. :)
Good points Steve .
You will find that the cells are very small in area that this happens in , been there done that , wore the T-shirt out . Look at a Holden tune and Lean Cruise , you will see that the area is just a few cells .
By nature OLSD is not mileage friendly , but with the COS that can be fixed .