aiight, well after reading over all the stickies under the TBI section for the 2nd time around.. and absorbing what BMonteSS had to say about DIY tuning he touched on few things on tuning MPG in general. now i want to know who has the BEST MPG that they tuned or something that they are proud of? i have a 383 stroker, switched back to 61# injectors and plan to run it at 30 psi to start tuning. I will have a VAFPR as well, in combination with Ostrich 2.0 and obd1-to-usb cable. i learned that performance and mpg are totally different.. but i want to have mostly mpg and all performance when i do get on it.. does this make sense? My stock 350 C1500 managed 20-22mpg consistently on the hwy, this was with EGR and working 02.. when 1 of the 2 failed it would cut my mpg down to 15mpg. when both failed, my worst was 10mpg. my 383 has no egr, will this effect total mpg outcome? i do alot of hwy driving, so i would like some answers, as this is my main reason into diving into DIY tuning. can anyone help? right now my 383 is somewhat tuned, but mpg sucks, and i swear im getting about 8mpg or so. On my 12 miles drive to the dyno it drank 20 something gallons, but came to find out my TPS was wired incorrectly. It left a train trail of black smoke all the way to the dyno. After that, we repined TPS, and he tuned it somewhat better, but MPG royally still sucked with the BBC injectors. I switched back to the SBC injectors, and plan to run them at a higher psi, for better mist spray and better atomization. any insight? or expected mpg i can accomplish once dialed in correctly on a MPG tune? suburban - 4"lift 33" tires 3.73 gears (soon to be 4.30 w locker) 383ci k1103 cam let me know if more info is needed.. but stock height, and 350 combo it got 20-22mpg: so something is very wrong... stock was 87 tune, my 383 combo uses 93 tune.. and guzzles even more!

I'm thinking that with the frontal area of a 747 the fuel mileage isn't going to be all that good anyway. Lifting & huge tires increase air drag a bit.

OTOH, you need to get your tuned settled down. Set the injectors, TBI, and fuel pressure and leave it for a while. Then work on the AE along with the VE tables. Once the fueling is in line then work on SA.

If there is a lean cuise mode that can also be enabled (once the fueling & SA is in line).

RBob.

Im gonna follow this post pretty closely and see what you can come up w/.
Ive been working on a very similar problem for the last 3 months!
'90 jeep wrangler 7"s lift, 33x 12.5 tires, 3.55 gears, 350 TPI (speed density), w/ t350 tranny.
Ive got alot of it straightend out (i think,LOL), but the best mpg I have gotten was 11.3, and that was only ONCE! My average is low 10's.

I just started to get into the highway mode section, but low and behold, my last fillup was 9.3mpg
Im kinda running out of ideas of what to try next. I think it runs better when the laptop isnt on, that way I dont know what its doing ,LOL

Jeff

there is a lean cruise mode in the $0D bin with the 7427 computer like you have. once you get your ve table nailed you will want to enable this mode. but dont try it without your ve right and a wideband hooked up to verify your afr while in lean cruise. not having an egr will probably hurt you mpg some.

this quote come from Haulna$$

"Yes, there is a lean cruise mode. Some calibrations use it, some don't but it is easily enabled. By enabling the "Open Loop AFR Enable" flag (L400D, bit 0) and ensuring that the min temp setting constant at L48C7 is reasonable, the PCM will use the "Open Loop AFR vs Coolant Temp vs Vacuum" table in closed loop. This table is always used in open loop but by enabling the above parameters, these AFR's will be targeted in closed loop. I have verified this by datalogging desired AFR in place of Batt Volts. BLM's will be affected in closed loop when the desired AFR is above or below stoich. When tuning fuel, this should be taken into consideration to ensure VE table accuracy. When I tune open loop fuel, I disable EGR (and block it off to prevent any valve leakage) as well as CCP and Cat converter overheat protection then bypass the Cat (I run with a gutted one). This cuts the fueling modifiers down to AE and PE. I then set the table values in the operating temp range to something like 13:1 across the board and datalog desired AFR vs WBO2 AFR and adjust the VE accordingly. This ensures that the VE tables represent actual VE and not some fudged value. When I move to closed loop, I disable lean cruise and tune the O2 thresholds for BLM's of 128 across the board knowing that my VE tables are accurate. This is especially helpful when the factory O2 sensor has moved from the factory location. Once thresholds are tuned, I move on to proportional gains to get the O2 voltage swings where they need to be. Once all this is set, I enable and tune lean cruise. Oh yeah, I forgot AE. I tune AE in open loop with the WBO2 as well as WOT AFR."

that is how it works. this method of tuning might ruin a cat converter if you have one, and i dont know how lean cruise effects a cat but it might not be good for it either. maybe some smarter guys can chime in on this stuff. the problem is i dont think many people on third gen are running a 7427 ecm.

You want mileage? Lose the lift & tires. You want lift & tires? Buy more gas... that is all.

Sorry but I don't have the tbi. But will offer some words of wisdom.

Years ago I set up my 72 blazer 4500# 427 BB small round port head with a wide ratio 4 speed 3.07 rear gear.

each gear was 1/2 the last so at 3000 rpm = 80 mph in 4th, 40 in 3rd, 20 in 2nd 10 in 1st. get the picture.

any way ran a rv cam 1000 - 3000 .5 lift 212 dur, dual exhast. on top was the 650 cfm Qjet, the small one. set the secondaries not to open till 3000 rpm tuned the primaries lean, sec rich, 3-6 in vacuum power valve. this 4x4 brick got 16 mpg highway 13 city. normal for that setup was 13 hwy 8 city.

It was very torqy and responsive but nail it and off to 100 mph u would go.
It would pull from 1000 rpm (26 mph 4th), great in town, all the way to 4000.

If you are looking for mpg ya need to know what rpm and load you run while crusing, say 55 mph and ? vacuum (load). tune leaner (for mpg) under that spot and tune for power over that spot. As hold off pe till over that spot.

I hope this makes sense. It wouldn't be good as drag racer but would be fun and affordable to drive.

its the simple comments like this that dont need to be posted. read back over what i said! I KNOW EXACTLY what my truck is capable of... my suburban got 20-22 MPG on average hwy! city I got 16mpg with a light foot.... being a 2wd! and being a BRICK on wheels..

with lift and tires i expect 4mpg or so to be sacrificed with everything working proper in the tune; and thats mostly lost from the big tires... That said my truck should be getting ATLEAST 17mpg hwy now! I still run my stock airdam under the bumper as well!

when i went from 235 to 265 i lost 1mpg, going from 265 to 318 i expect to loose 1.8 more mpg! now figure in the lift, thats where i get about 4mpg lost total!


getsideways: thank you. this is exactly what i was looking for, a method to start with when i start tuning, so i stay on course and get the proper steps in order 1st.. so i will not be back peddling. About the Kitty, I have none! So im not worried about burning up a cat... My 3wire NB02 is further back, immediately after the collector on the passenger side long tube header!

Being that you run a 7427 pcm, Ill prob be asking you some questions in PMs and such.. but i definitely want to enable lean cruise mode. And proceed with the steps listed above, when i start tuning it.


pandin: at least you also know as well that big trucks/suvs CAN get good MPG! its all into the tune.. my combo works pretty well its setup for gobs of TQ.. I barely touch the pedal and the trucks keeps moving on its own. at 80mph im around 2400 rpm in OD.. at 60mph im at 1900 or so in OD this is with 3.73 gears and 30.6 tires instead of my 33s which i hadn't install yet.

the tune is whats throwing everything out of whack as far as mpg, and im about to change that with the help of you guys. I know its not a 3rd get or some tiny car, but please don't tell me my truck will never get good mpg when i know for a fact it can! and has before!

most guys with stock engines get 12/15 mpg in their trucks, I am getting even MORE than my original window sticker even stated! and I always have, why? cause i keep everything in proper order and I know what my truck likes and is capable of.... Im the original owner.



what i want to do is make my tune even better than GM did, if that makes sense... GM did a excellent job for me to pull those WAY better mpg numbers.. more like 16/20-22 hwy!

so i would very much expect you lighter guys to be doing much better than I am with you guys custom tunes.. if yall are getting equal or the same mpg as me.. then something is VERY wrong in you guys tunes as you guys have much lighter vehicles! i would personally expect near 30mpg in a 3rd gen!

now all of that said, i went from a stock 350 to a 383.. which produces more TQ all across the board. Im realistically expecting 17hwy mpg, which is above average for a V8 in a brick this size and near 6000 pounds. hauling around 42 gallons of fuel & 8 passengers...

4"lift with 30.6 tires

further more i sit up only 2" higher than a stock 4x4

i can understand if i had 12-14" of lift or something.. and you guys started ragging, but come on!

i know for a fact that 383 tuned well can average 19mpg hwy. weighing about 4000#s... this is why i stuck with a 383, and didnt do anything major or went BBC engine. as i had mpg in the back of my mind.

its plenty of FSC guys who gained 1mpg hwy with their 383 in same truck, lost 1mpg city... alot of them mpg stayed the same, as the 383 was more efficient sort to speak. most noticeable gain was 2mpg less with a mild 383.

91chevZ71 on this forum and FSC has 6" lift on a 4x4 with 35s, and gets 19mpg... so BS who says it cant.

sorry for the rant, but i didnt expect this. i just need HELP!

unless you have some killer road burning motor, you should be able to get some decent hiway mileage with light throttle use.
a friend of mine regularly tops 22 hiway in his 4" lifted, 33" tired Z71, his best was about 24 hiway with a CTS that was reading high. he does have higher gears than you do, he said they are around 3.08s & he does have overdrive. his truck has not had any chip tuning done.
with my stock TPI, in town is anywhere from 14 for the low with a best of about 20. the difference isn't in the amount of traffic, its in my use of the go petal. my normal average is 16~18.
i have gotten a best of 29.7 hwy. i wasn't just rolling along at or below the speed limit on the trip, i was a few mile per hour over it most of the time, & i spent some time up close to 100 too. i had the A/C on & i was using cruise control. the cruise probably hurt me some as i was driving through east Texas.
i know there is more in it with better tuning & more aggressive use of hiway mode.
not having EGR i believe will hurt you some on using hiway mode. with EGR you can add a little more timing.
the rest of the tune has to be close before you start playing with lean cruise.
your gearing will also hurt you a little bit too.
i didn't notice if you have a wideband O2 or not, i'll tell you it does help with tuning. using one it feels almost like cheating.

What is your current measured MPG? You will need a base line to start with.

And, as I previously posted you need to stop making changes to the mechanicals. Pick the injector size, pick and set the fuel pressure, set the base timing, install the TB you want to use. Then LEAVE them.

While leaving those mechanical pieces in place start tuning. How does the VE table look? Are the BLM's in line? How are the transitions? AE, DE, PE, all OK? Then the SA, any knock? Any hesitation? Any areas where power is low? Any areas that are rough?

Have you been keeping track of the MPG during all of this?

Now enable the EGR and tune that in. BLM's still look OK? SA good? Driveability is good all around? How's the MPG now?

RBob.

FWIW, I have a 1993 suburban, 2500 4wd. STOCK! 350 w/4l80e, 4.10's in the front/rear (factory). It has a 3inch BODY lift, and I run 35 12.50 16's, the mileage is about 12 city. I have to measure it up to be sure, this is the wifes beater. If I put the stock tires back on it, then I MAY pick up a mpg or 2, but this is how this has always been, for my vehicle anyway.

At 1900 rpm @ 60mph you need to make sure you aren't close to PE. EGR will need to be utilized for the best highway MPG. IMHO

FWIW I also tuned a stock 76 350 nova auto 350 TH, Qjet 4 barrel, fac cat. It was rated sticker at 12 mpg highway. Changed to stock 74 factory duals two pipes 4 hole muffler two tails (no cat). rejeted primaries richer. disabled APT (automatic part throttle). put in a 3-6 inch vacuum power valve spring. secondaries in at 3500 rpm (air valve spring tension). changed dizzy weights and springs for more advance.
got 20 mpg highway. actually drove from zanesville, ohio to down town baltimore, md 395 miles on a 20 gal tank of gas. speed limits were 70 mph then.

It can be done, my own TPI 305/4L60/3.08 combo knocks down 21 mpg in a fullsize van running 70-75 mph down the interstate and gets about 16-17 mpg on a daily commute in town.

So, weve found out that the high teens are doable. I almost would have liked to here that it will never happen, that way I can just give up and deal w/ it
The odd part is that Ive heard these replies and others about people getting good mpg w/ , Ill just call them big trucks, and most of them were doing it w/ good ol carburators? Wow, just blows my whole idea that EFI is the efficient way to go.
One thing I can check is if im tipping into PE during cruise, as mentioned above.

A question w/ highway mode,
What is a recomended target AFR for cruising between 55-60 @ 45KPA?
currently Im set at 15.5 but it runs around 15.1.
Also, Ive yet to add any extra spark advance during this. Could this help increase my mpg?
What would be a safe amount to add at the same cruising conditions as above?

Im not looking to hijack this thread, just adding more to it. I hope thats ok.


Jeff

I'll give you a couple of clues:

1) log the accumulative fuel and distance counters found in the ALDL data stream over the same piece of road under the same conditions so that you know exactly how much fuel was used over distance X

2) work the AFR up and down until you get the least amount of fuel used over distance X, now do the same with the spark advance.

3) repeat steps until you see no improvement

Go slow, take notes. Probably want to experiment with EGR on / off as well ( I don't have it myself ) My engine is happy around 15.3 and 34 degrees... but each is different...

yup, thats what im doing. I ONLY drive back and forth to work. 15 mins one way, 55-60mph most of the time w/ just one side road (hill) thats about 2 miles long.
I also get my gas at the same place every time because some of our stations around here are using ethynol and some are not.

Im also watching my tps volts to see how much I have to "push" it.
I avg. 1.17 volts while cruising @ 55-57 mph.
Anyone else care to compare?

The point to be made is Factory tunes suck. not carb vs efi. the more mods you do and the farther from factory stock you get. The more important the tune. Remember stock means the engine, the vehicle, and the way it is driven.

I learned from working on my friends K5 blazer that these types of vehicles run in a very high map range, all the time.

His was a stock L05 with a SD TPI swap. It idled at 35 kpa, and as soon as he put his foot on the gas, map would hit 70-80 kpa and stay there. I had a helluva time trying to tune that thing.

It was lifted 6" with 33's on it. His mileage did improve by 2-3 mpg over the tbi that was on it, but it still wasn't anything he or I were happy with.

I should have disabled PE and perhaps that would have helped.....

-jason

exactly correct.

Iin the late 70's the smog cars ran a 12"-14" vacuum power valve instead of 3"-6". What that mistery thing (vpv) does is pull against a spring.

With high vacumm the primary metering rod is seated lower in the main jet, leaning the fuel mixture.

With lower vacuum the spring over comes the vacuum and the primary metering rod raises moving the narrow part of the rod in the main jet richening the fuel (PE in efi). the differance was 26%.

What does this have to do with tuning efi?

VE vs map For each inch of vacuum there is a map value. 0" = 100 map

engines are engines, do not care what feeds them just so it tastes right.

If your load, speed, rpm, combination crosses the PE line then MPG drops. by 26% or what ever you or Factory have set.

If you tune for 14.7 afr at the highest steady state load then your milage will be X
When you enter PE mode your milage will be X-26%. 14.7 afr - 26% = 10.8
afr. BTW 14.7 afr + 5% = 15.4 afr (highway mode) 15.5 afr HM 12.6 afr PE

PE 20 mpg - 26% = 14.8 mpg HM 20 mpg + 5 % = 21 mpg


The tall tires (36") and tall gears (3.07) are like putting extra weight in the bed.

I hope maybe this will help clear up what is going on and where the mpg is being lost.

Remember too that high loads and lean AFR's = lots of heat.

If you drag/street race PE should be invoked at off idle. Helps make tires spin.

Keep this info flowing, it gives me and hopefully others, different things to look into.
As far as MAP and me go:
30 kpa @ idle
55kpa @ mid to high 50's mph @2500 rpm w/ TPS % in the low 20's
That dosent sound extreme, Does it?

Im using the 8d. xdf and im still trying to make sense of all these "enrich power, and, enrich accel" settings. However, it looks like my chart "power enrich enable % TPS" is set for pretty high TPS%

rpm / %tps
4800 / 80.08
3200 / 80.08
2000 / 69.92
1200 / 60.16
400 / 50
Im thinking that w/ these settings, Im no where near PE while Im cruising. Am I right or is there something else that can trigger it?

By the way, what is a delta event? Ha, sounds pretty impressive, guess I better go look it up

I have never used 8d so... This is going to be genaric type of info.

If your blm's are floating around 128 at cruising speed and everything else is working. Your AFR hopefully will be at 14.7. This is your base to tune from. If they are locked at exactly 128 then you are in pe mode.

The first thing to know is with mpg, torque is king. the engine needs to run right at peak torque at cruise speed. The cam and gearing must be matched to get good results. The more the miss match the harder it is to tune and lower the mpg.

My 72 Blazer's peak torque was at 2000 rpm @ 53mph.

As jaysz28 found out. Miss matched parts are a bear to make work. I would suspect that the cam in the K5 was a lumpy low vacuum one. Thats why the map range was so narrow. also rpm's were likely running way under the peak torque.

jcs64 would you know what your idle and cruise vaccum is vs map.

Delta means change the higher the delta the faster the change. ease on the gas low delta. smash it to the floor high delta.

My $32 chip has a min load pe enable. It is set at 50 lv8 (Maf system) the engine (383) idles at 50 +- 5. The idle is richer and low speed mpg is less.

For the ones following this post.

Just think the Factory has many engineers, fancy computer simulation software, unlimited parts, and a test track. They take years to sort out what needs to be done. Our tuning is not going to be perfect in a day or two.

I never checked vaccum at cruise, but Im pulling 20"s at idle w/ a map of 31KPA.
I can check cruise vac. tommorrow, I do know that the MAP is around mid 50's kpa.

When PE comes in and the AFR changes, would this show up as a new "target AFR" in TP RT? (so that way I can seeif im "in it")

I must have somehow signed into the wrong site. For some reason I was thinking that 3rd gen F bodies were 82-92 Camaro's and Bird's.

Anyway, our 92 RS was getting 28/29 mpg when we sold it, my 89 was getting 24/25 before the engine took a dump. Neither one of these had a 4" lift or 39" tires.

right now its under 10mpg! it was fouling plugs b4, so its not too accurate. i will get a accurate number shortly.. i know a basic tune should fix this to about 13-14. but i want more than just the basics, as im after mpg, and i know it will take some work.. i want something like 46% tps = balls to the wall tune.. anything else mpg.. i hope its do able.

i will have plenty datalogs and stuff, as soon as i get the things to start. i have SALE in the Classified section of L05 parts, if anyone is interested!

Im not going to switch the combo again.. I did just bought some 4.56 gears for the truck, but im waiting till i get a locker, and hopefully i can re-tweak my tune a little for the new gear. I also dont have EGR with my LT headers or intake manifold..

very good point and methods. im going to start in a controlled environment/street with cruise control working. I also dont have EGR on my new engine.. im going to attempt to tune it without it as well.. Since i built this engine, I prob put only 7K miles on it!!

Pandin: you sure seem VERY knowledgeable about setting up for best mpg. I know each engine is different and has to give em what they want.. what do you think of my 383 with 4.56 gears and 33" tires? i kept reading and people are gaining mpg in city, and hills etc, with that gears. and some even increase on hwy! all with the particular 4.56/33 combo. I found out with my camshaft my engine powerband is: 22-2600 RPM... that said, i was told anything under 70mph should yeild good mpg...

at 80mph & 33s with 4.56 gears ill be at 2800 rpm

It is real simple cruise mph = peak torque rpm = max mpg

For your engine 2400 rpm will be the sweet spot. but remember vehicle (weight), tune, and driving habits will make that differ from some one else's.

aiight, well thats simple enough.. glad i got alot of TQ to work with and my curve is flat all across the board.... so maybe i can pick a spot near peak, and level it off with a lil higher cruise mph.. ill just have to play with it, to how i like to drive.

you guys keep this thread going, cause its tons of good info already, not just for me, but for everyone, in whatever vehicle they got. ill be asking more questions in a few weeks, when i get data.

Do you mean if I put my car in 1st gear, and ran the engine at 2400 RPM, I would get the best gas mileage? What if I shifted to second? would it get better? What about 3rd gear, even better? How about 6th gear? I get much better gas mileage at 1200 RPM in 6th that I do at 2400 RPM in 4th. If I try to go faster in 6th, the mileage just goes down.

It is true that you will get the best brake specific fuel consmption at the torque peak, but not the best gas mileage. Two different things.

Scot

I assumed that checking mpg would be in top gear. Peak torque is at your max VE. For avg vehicles best mpg is just below PE. If you can keep the vehicle moving and not lug the motor and stay out of PE, mpg will be max.

1965 VW 40 mph up hill, 80 mph down, 40 mpg, no gas gauge only reserve lever. 35 HP, 1000 cc motor, 4 speed.

But if you are building a heavy weight 4 x 4, the closer the cam peak torque is to crusie mph the easier it will be to tune and not be in PE.

How about the drive 35 mph (old old school thinking) for best MPG what gear would you be in?

My car gets 20 mpg, at 70 mph, 2000 rpm, OD lockup; better 25 mpg, at 35 mph, steady driving; and even better at 44 mph, just after OD lock, 30 mpg 1200 rpm, flat road real steady speed. 300 hp 400 tq 3500# car. BTW 15 mpg city

Here are my results from the TPI ECM in the Van that I recently switched to and started tuning. I am still running a mostly stock S-AUJP V4 tune with minor changes. The engine runs pretty rich all across the board, the VE tables are off, the NB O2 sensor trigger voltages are off, and the timing is pretty weak. Not the makings for the best fuel mileage, but it still did quite well for running around town. I've driven it everyday this week to and from work in city traffic and got 16 mpg this tank.

These are the various tables that I use to tune with when using ScannerPro now. Regardless of the PCM/ECM you are running, if you know the datastream's output, you can obtain these outputs.

Average Fuel Economy


MPG vs MAP vs Speed
[IMG]

BLM History Average (WB-AFR vs RPM vs MAP)


Wideband History Average (WB-AFR vs. RPM vs. MAP)


Wideband vs Narrowband Correlation (WB-AFR vs Command AFR vs RPM


Timing Advance vs RPM vs. MAP


Timing Avance vs RPM vs % TPS


Spark Retard vs RPM vs MAP

Here is a map to in hg table.

Kpa_ in hg .....Remember that old pre smog carbs used a 3-6 in hg power valve.
0.0 = 29.9 ......and smog engines used 12-14 in hg.
10 = 27.5
20 = 24.0 ......Look at the mpg vs map vs sp table above and see that from 40 to 50 map
30 = 21.1 ......How much the mpg changed.
40 = 18.1
50 = 15.2 ......If pe didn't come in to 80 - 90 map like the old carbs. How much differant
60 = 13.1 ......mpg would be at a 14.7 afr at 60 mph? 18/19 instead of 12 mpg ?????
70 = 9.3
80 = 6.3
90 = 3.3
100 = 0.4

I can show you what to do and why, but not how.

Ask the right question to the right person and you will get the right answer.

To delay PE fuel, you can raise the TPS vs. RPM table to allow more throttle before PE comes into effect, you can increase the time delay and raise the RPM clickover. Normal GM ECMs look for 3 things for PE. First the coolant temperature has to be above a certain threshold. 2nd the throttle must be open a specified amount or greater (changes at different RPMs via the TPS vs. RPM table) 3rd the time delay must be expired OR the RPM must go above the limit. My Van running down the road, the PE is set for 35% throttle and is delayed for 15 seconds, unless I cross 2,500 rpm, then it is immediate.

What mph is 2500 rpm and where is throttle % at that mph?

Here is a MAP to IN/HG to Fuel Economy @ 75 MPH and 2,000 rpm table.

Kpa_ in hg-----MPG @ 2,000 rpm
0.0 = 29.9-----??
10 = 10.5 -----38.18
20 = 24.0------30.78
30 = 21.1------24.11
40 = 18.1------19.33
50 = 15.2------16.22
60 = 13.1------13.19
70 = 9.3-------10.17
80 = 6.3--------9.53
90 = 3.3
100 = 0.4

See a trend that directly correlates to where your foot is on the throttle. Once I get the O2 windows and Proportional Gains done(Make 14.7:1 actually 14.7:1, instead of 13.3-13.5). I will go in and turn the EGR back on, then I will dial in the EGR tables. At that point the fuel economy should be phenominally better.
----------
~100 mph, I am running about 50-60% throttle in OD. In 3rd gear 2,500 is about 70 mph. The PE table was really dialed in to be used with light (5,000 lbs and less) towing in 3rd gear. I run about 30% TPS (52mm Throttle Body) going down the road pulling a 5,000 lbs tandem axle trailer in 3rd gear @ 2,500 rpm. The PE is set for about 40-45%. A long highway grade will pull me up around 50-60% throttle and hold it there, PE is needed because it engages and provides cooling for the pistons and more importantly exhaust valves and cats.

If you are pulling 5000# trailer and a G20 (with tools?).

your mpg is great!!!

The 5K# trailer is a boat, I get about 13 mpg pulling it on the highway. Just the Van (5,300 lbs) unloaded is the mileage I quoted. The mileage is still quite good for the power/weight it has. I don't drive it easy, witnessed by the log that ends in the triple digits.

I got a 2000 1500 silverado (4000#) 2wd reg cab long bed, 325 290 hp stock.

hauled a 84 monty (4000#) to Erie PA, (kid's) tandum trailer. got 14 mpg for the trip, loaded up, empty trailer back. south of Cleveland with cruise on 65 mph it down shifted clear to 2nd on a hill. mostly ran in OD. usally gets 20 mpg trip.

No, that's not right.
If you map out the fuel consumption vs RPM and torque, you'll find the sweet spot is lower than peak torque, and about 80% load, typically. But, in order to get to that load for a long time would need to be pulling something (but your MPG would be bad because you're now doing more work). Most cruise is much lower load.

If you had a way to display BSFC, you could know the best economy, but you'd have to have calibrated the engine on a dyno, and have a special MAP of torque at each RPM and MAP, and then compare that to the pulse width and RPM (i.e. injector duty cycle), and then compare that to the vehicle speed for mpg.
You can go directly to MPG (from duty cycle, static flowrate, and vehicle speed), and then drive at various speeds in different gears, and find the sweet spot. You'll likely find that OD + lockup at a low speed is best economy, nowhere near torque peak.

Which has been exactly my point all along. If you were to calculate the loading on the engine it would be 75-85% at part-throttle cruise where you find best fuel economy. The MPFI Camaro 3.4 in my S10 Blazer is under a pretty heavy load at lower rpms and still delivers great fuel mileage.

BSFC is lowest near peak torque, but fuel economy definately is not at its highest.

Sorry, but I disagree with that too, and have several engines' test data to support it. But, it would be un-ethical to post it. Peak torque can be affected by many things, such as intake manifold harmonics and thus cylinder filling.
BSFC is just where there's a balance between friction (i.e. RPM), pumping losses, burn speed (mixture, swirl, and spark timing). Cylinder filling % isn't really a direct factor, because EGR and lean can help BSFC, while both hurt peak torque.

Hey Fast305, ive been trying to get scannerpro to work on my 95 with no luck. do you have a working adx for $0D bin? would you be willing to let me try it? thanks

Okay I understand what you guys are talking about.

My question as load increases, same engine, load beening, selling the s 10 and installing motor into 6000# 4 x 4 van, increasing the load. now motor is a lot smaller than vehicle . would the BSFC increase to a point at or nearer to peak engine torque or would stay the same.

Or think this way not engine BSFC but the vehicle BSFC.

I hope I ask the right question to get the right answer.

I understand this.

For my car (3500#) the computer estimated that 12 hp is used at 50 mph. Which is 1500 rpm. Peak torque is somewhere around 3000. cam is 1000 to 5000.

Take that same motor and install a RV cam 1000 to 3000 rpm. put that combination in a 6000# 4x4 van geared for 2000 rpm @ 50 mph. would the sweet spot be the same?

My point is, with a heavy vehicle/under powered motor, (optimized for peak torque, at the driven cruise speed), (be that 30 mph or 85 mph), will get better mpg if it does not enable PE.

keep the good info coming in... they said gas is going to hit $4.00 in a few months this summer, and that is for regular octane. Premium is prob going to be about $4.20-.40... A barrel is like $105 now! A all time high... we need to do what we can with our cutsom tuning. If we want to drive these things... But i dont think the government want us to drive anything...

its a good months aways from summer, and right now gas is like $3.69 a gallon for premium!! I can guzzle that just exiting the station, it dont makes sense. $3.69 X 42gal = $154.95 When gas was still .99c x 42gal = $41.58... this was just back in early 01 even.. WTF!

we ALL need to bookmark this website! >> http://www.gasbuddy.com/

TbiMAX you wrote-

"when i went from 235 to 265 i lost 1mpg, going from 265 to 318 i expect to loose 1.8 more mpg! now figure in the lift, thats where i get about 4mpg lost total!"

Now I'm asking an obvious question that you've probably thought of but...

When you are changing tire sizes you're also getting different tire OD's. Have you taken this into account? For example- if you increase the tire OD and don't recalabrate the speedo you'll actually travel farther per mile than the odometer will report. If you calculate milage based on the reported miles driven then your actual MPG will be slightly greater than figured. In other words if you don't recalabrate your speedo then the "loss" of 1 MPG may have not actually occured.

With all else being equall a taller tire should net MORE MPG by raising the effective gear ratio. But as you may know the real world doesn't always react that way. Sometimes a LOWER effective ratio may net HIGHER MPG's if it puts the engine in a more efficient torque range. $.02.

I wish we had those prices, here in Sweden Euro 95 octane is $7.77 a gallon today and prices are going up.. so i really would like to get a good mpg tune.

Add air pressure(tires) to the maximum manufacturers specs. Less rolling resistance.

I thought I read that commercial truck.bin's often have the TPS % to allow PE set quite high as compared to passanger cars? maybe set it at that point or 5% higher.

In my .bin PE-TPS % is from 50% @ 800-1600 rpm up to 60% from 3200 rpm. I alredy have max pressure in my tires and have put 235/75-15 instead of the 275/60-15 i had before.
I hope the EBL will do some good for my mileage, and so far it looks good.

Consider a spare set of skinny commuter tires? LOL