Gas Mileage

[0xDEADBEEF]

Well GM did leave a ton of efficiency on the table with the TBI due to the lack of technology available at the time to meet the emissions requirements. The lack of an IAT sensor and un-heated 02 sensor causes the fueling to drift all over the place. The heated sensors were installed after the Y-pipe as well for a more accurate representation of what the whole engine was doing AFR wise. The single wire sensors have a ~30K mile life and fall off drastically in accuracy after that. When they fall off, they fall off in the overly rich direction causing much higher CO and HC readings and atleast a 2-3 mpg loss. The pellet box cat in addition to being overly resctrictive was only capable of reducing HCs and CO, not NOx thus EGR, richer mixtures and limp wristed timing advance. The pellet bed also has a tendency to clog and become even more restrictive or the screen material inside fails and fills the muffler core with the beads, choking it. It is fairly easy to get 3-5 mpg better out of a TBI especially an earlier one. I added long tube headers, dual in/single out high flow 3 way cat, a K&N filter and tuned a ~200K mile L03 305 years ago. Made more power at the wheels than GM rated it at the crankshaft and gained about 4 mpg. That 305 made 18 ft/lbs more torque than my stock L31 made at the wheels and only 8 hp less.

Higher fuel pressure does offer a better spray pattern and promotes better fuel atomization and distribution in the manifold. GM went to smaller injectors running at 30 psi to help this later on.

Your basically saying because of broken or worn parts lambda was much less than 1. Ok, that's not surprising.

TBI is an old design that isn't as good as current designs, no doubt, but at a steady state rolling down the road it's not going be 5 mpg off.

 

[99xcss4]

we all want to get the best mpgs we can that is all fine and good but it seems that some people have unrealistic goals in mind to me any way if you go off roading your mpgs go down if you tow or haul or both your mpgs go down if you have a heavy right foot your mpgs will go down if you have big tires or big wheels your mpgs will go down I think most people know this all ready but for those that do not these newer trucks with big 4 cylinder turbo engines and 6 cylinder engines both na and turbo do not last as long as the old v8s that $#!+y auto stop start puts alot more wear on the engine and the modern truck are so big and heavy that those litle engines are working harder and if you actually use them like trucks they get wore mpgs then the v8s get the way I see it if you can get your truck in the high teens on the high way you are doing great

 

[L31MaxExpress]

Your basically saying because of broken or worn parts lambda was much less than 1. Ok, that's not surprising.

TBI is an old design that isn't as good as current designs, no doubt, but at a steady state rolling down the road it's not going be 5 mpg off.

I have seen them double their fuel milage correcting running issues. It is very easy to lose 5 mpg. Failing front brake hoses and the resulting warped front rotors from brake drag had my highway fuel mileage on my 97 down about 7 mpg at one point. Power wise felt like I was dragging a bus. Discovered the problem after I parked it after a 30 minute highway drive and both front wheels were smoking.

I have also seen a dead knock sensor kill 3-5 mpg and about 50 hp. The truck was a 95 and the PCM was running at maximum knock retard the moment the PCM enabled the knock sensors ability to retard timing. The truck struggled to get to 80 mph even at WOT.

 

[2Grim4U]

Please read the thread before posting, its not that hard to read through 3 pages. It was explained a few times already.

Right on y’all have a good one.

 

[Caman96]

But we’re talking about an 88 Full Size Blazer, that brand new, only got 11-16 mpg, but now 36 years later is getting “in the 20’s” with 33” tires.

 

[0xDEADBEEF]

But we’re talking about an 88 Full Size Blazer, that brand new, only got 11-16 mpg, but now 36 years later is getting “in the 20’s” with 33” tires.

Full parts list:

K&N filter
Intake Vortex Generator
Slick 50 oil treatment
E3 spark plugs
Magnets on the fuel line
"Power conditioner" in the cigarette lighter
Removed tailgate

 

[Caman96]

Full parts list:

K&N filter
Intake Vortex Generator
Slick 50 oil treatment
E3 spark plugs
Magnets on the fuel line
"Power conditioner" in the cigarette lighter
Removed tailgate

Yeah, who needs a Prius?

 

[99xcss4]

But we’re talking about an 88 Full Size Blazer, that brand new, only got 11-16 mpg, but now 36 years later is getting “in the 20’s” with 33” tires.

I agree with this by those numbers that mean when frank'n truck is done even though it is a extended cab long bed K-2500 454 tbi 4l80e with a 3 body lift 6 inch suspension lift with 37x12.50x17 mounted on 17x9 wheels and will either have 8:88 5:13 or 5:38 gears that it is going to have fuel economy in the mid or high teens I all ready know it is going to be a gallons per mile thing that will pas any thing but a gas station

 

[99xcss4]

Full parts list:

K&N filter
Intake Vortex Generator
Slick 50 oil treatment
E3 spark plugs
Magnets on the fuel line
"Power conditioner" in the cigarette lighter
Removed tailgate

hahahahaha what a joke on a side note being serious I have all ways been a little curious about those e3 plugs never tried them though

 

[L31MaxExpress]

But we’re talking about an 88 Full Size Blazer, that brand new, only got 11-16 mpg, but now 36 years later is getting “in the 20’s” with 33” tires.

Very possible. One of the first things I do before touching an ECM is get fuel economy both instant and average into the datastream so that it is in the datalog. I correct the math used until it the average very closely matches the hand calculated number for the same trip. I use the data to be able to tell how timing and air/fuel ratio changes effect the fuel economy. Sometimes minimal changes make a huge difference there.

I had a heavy old box of 88 Cadillac Brougham that was EPA rated at 15 city, 22 highway and 18 mpg combined with the stock Q-Jet fed 307, 200-4R and 2.53 gears. Running a 403 with W31 350 heads and intake manifold with a custom mondello cam and GM 454 TBI with an EBL running it, the old car averaged 26 mpg in mixed driving and knocked on 30 mpg on longer trips. Nearly a 100 CID larger engine, more than double the horsepower and better fuel mileage. Then again the 307 with the Q-Jet often managed 27 mpg on long trips vs the 22 mpg it was EPA rated. I take the EPA ratings with a grain of salt, especially once the vehicle is no longer completely bone stock. It is very possible to increase the fuel mileage on an older vehicle. Age does not dicate whether an engine is running in a better state of tune that it was from the factory. Even something simple, like I always cheated on my initial advance on a TBI by 6-10* BTDC vs 0* and always found they ran much better.