So what's the down side? It being disabled make no sense to me in a day and age with CAFE, unless maybe more emissions... maybe NOx?
Engines tuned to meet USA (and Canada, and maybe other places) emissions regulations need all the help they can get.
Richer mixture than stoichiometric increases carbon monoxide and hydrocarbon emissions, but they decrease when leaner than stoich.
Leaner mixture than stoich increases NOx emissions, but they decrease as the mixture gets richer.
NOx is harder to clean up than CO and HC. They'd like to run leaner than stoich, but they get killed on NOx emissions.
The CHEAPEST balance is to RAPIDLY switch from just lean of stoich to just rich of stoich, and let the catalyst store--then use--excess O2 in the exhaust to oxidize the HC and CO, while keeping combustion temperature low enough to inhibit NOx. Combustion temp is controlled with EGR and mixture strength, among other techniques.
Highway Lean Cruise (HLC) mimics what carburetors were tuned to do for
decades--allow the engine to run lean at light load without actual misfire. Stoich mixture is great for emissions, but not optimal for fuel economy. It's too much to hope for that the EPA and CARB would come to their senses to allow better fuel economy. They've already made Diesel engines nearly illegal with excessively-stringent emissions regulations. They clearly want to do the same with gasoline engines, in order to force us into hateful shitebox electric cars that will destroy our electrical grid.
The changes I like to make, after reading all the responses.
1: do a Highway lean.
How to make this mod? this mod interest me the most, sounds like a fuel flow mod.
I have the stock fuel injection for this year truck, like to research more on the fuel injection system.
Totally illegal at the FEDERAL level. But it's unlikely you'll get caught unless they do emissions testing in your area, and that tends to be a state or county matter. For now.
Would likely improve fuel economy substantially if you're driving habits match the parameters of Highway Lean Cruise. Won't make any difference if you always drive in town, or heavily loaded.
2: replace stock air filter with K&N OEM fit/on amazon for 69$
Ehhh. Not something I recommend on any vehicle that's got a MAF. I have K&N filters on several of my vehicles; with mixed feelings about them. (None of them are on vehicles with MAF sensors.)
As said, the big "normal paper" air filter is as good as it gets for the MAF-equipped Vortecs.
3: EGR delete.
I how do I update ECU as to avoid an engine light?
Is there a instructions on GMT400.com for that?
BAD idea. Leave the EGR alone. Fix it if it's broken. Makes a big difference in NOx emissions, can improve fuel economy in certain circumstances.
ALSO illegal at the Federal level to disable EGR. Also not likely to get caught unless there's emissions testing in your area.
4: open the exhaust .
Not looking for a loud sound, so maybe a chamber type muffler.
And a cat delete/or high flow. will the cat removed throw an engine light?
Deleting the cat is a bad idea. Illegal. A high-flow (monolithic) catalyst IN GOOD CONDITION doesn't reduce power very much, and you don't get complaints about the horrible exhaust smell from SWMBO.
Getting rid of the OEM muffler will likely make a big difference on the highway. Not so much at low throttle/low rpm like in-town driving. I'm told that the OEM muffler on the 7.4L 2500s and 3500s was a horrible, restrictive design--the inlet and outlet stubs were big enough, but the muffler piping inside the case (hidden) was tiny.
"Chambered" mufflers as typified by the Flowmaster brand, are more advertising bullshite than actual flow improvement.
5:change rear end lube to synthetic.
BTW, I have a 14 bolt/semi floating axle/from what i can find on the internet about this truck.
305/6 lug/C2500
How do I find out what gearing I have?
I do about 70 mph on the highway, am around 1800 rpm.
Fresh gear lube is unlikely to hurt, EXCEPT that there's a bulletin or two from GM; one warning about "positraction" additive commonly found in gear lube, being used on "Gov-Lock" differential cases. The excess positraction additive causes the Gov-Lock to slip and not function properly. You may or may not have
G80 "Gov-Lock" in your rear axle assembly. A second bulletin warns about synthetic lube in axles made before a certain date--the "synthetic" lube destroys the RTV silicone sealer on the early axles. Later axles switched to paper gaskets.
Truthfully, I'm suspicious of the synthetic gear lube destroying RTV silicone. I bet GM found problems with ONE brand of synthetic gear lube, under certain specific conditions, and is now recommending against ALL synthetic gear lube until the axle is switched-over to the paper gaskets.
START your investigation into gear ratio by looking on the decal in the glovebox. G80 is Gov-Loc differential case, the gear ratio is also likely to be with the "G" options. For example, GT4 is 3.73, while GU6 is 3.42.
Of course, you may have a non-original glovebox with the wrong decal inside. Or someone could have changed the gear ratio--or the entire rear axle--since the truck was built.
sell it and buy a corolla for daily
Wisdom. These trucks are never going to get the fuel economy of a shitebox car. There's plenty of trips I could take in a shitebox car, that are kinda wasteful to drive a truck instead.
My shitebox is a '98 Monte Carlo I inherited from Dear Old Dad. Before that, they were first-generation Lumina Euro 3.4Ls.
I dunno anything about this "highway lean" mod but the name alone sounds like a recipe for engine detonation, also makes me think of the problematic chrysler "lean burn" strategy from the 70s.
Not at all. Chrysler "lean burn" had driveability problems largely because the computers were hung off the air cleaner--high vibration, high heat, cheap circuit boards, prehistoric control of spark timing and carb mixture strength. YES, "lean burn" was a disaster, but mostly because the components were unreliable and not appropriately sophisticated.
Engine detonation can be monitored via the knock sensor. The main proponent of HLC on this forum has done so, and not found problems in his application. GM clearly found no problems with HLC when they used it in markets that were legal from an emissions perspective.
And as said--carbs were tuned to provide 15--16 to one fuel mix at light load/moderate speed for decades. This ain't new.
