if you have a stock, or close to, 2.8 3.1 3.4 and you are getting under 20 MPG - or, more accurately - getting 15-17 MPG - the problem is your ECM is NOT going into "closed loop". this is when the ECM will use O2 sensor readings to adjust the fuel mix. the usual cause for this is the thermostat. the engine needs to reach a certain temp to go into closed loop mode. it also needs a good O2 sensor. the "open loop" mode dumps alot of fuel in the fuel air mix, and will get you roughly 15-17 MPG.

quote Originally posted by Pyrthian: if you have a stock, or close to, 2.8 3.1 3.4 and you are getting under 20 MPG - or, more accurately - getting 15-17 MPG - the problem is your ECM is NOT going into "closed loop". this is when the ECM will use O2 sensor readings to adjust the fuel mix. the usual cause for this is the thermostat. the engine needs to reach a certain temp to go into closed loop mode. it also needs a good O2 sensor. the "open loop" mode dumps alot of fuel in the fuel air mix, and will get you roughly 15-17 MPG.

what about those of us that tried that and replaced both the O2 sensor and the thermostat?

quote Originally posted by Jermz238: what about those of us that tried that and replaced both the O2 sensor and the thermostat?

WinALDL - verify open/closed loop - check sensor outputs. especialy the MAT & CTS

I have a 1986 GT with the 4 spd. Best was 24mpg with a rebuilt motor at 60-65mph. with my foot on it a little about 19-21mpg

My 1987 GT, 3.4L with 4-speed automatic gets up to 36mpg on the highway, 28 around town, if I keep my foot out of it. I was amazed with that mileage when I took it home after the swap. The extra range is a bit of comfort because the fuel gauge is more of a "suggestion" than an actual measurement.

Was getting about 28.5 mpg on 84 with 4.10 gears in mixed driving. But this last tank after new air filter, pcv, and o2 sensor, I only got 24.7 mpg. Even though the Camaro will knock down 21mpg consistantly, its a lot easier to do the $20 a week fill up.

3.4 DOHC with a Quad 4 Getrag, I average 24 mpg.

86 GT with Muncie 4 speed. Drive 65mph about 70% of the time and get 24mpg no matter how I drive.

In my '86 SE V6/4 speed I can depend on 28 on the highway and 20-22 around town. My '86 Sport Coupe 4/5 speed gets almost exactly the same mileage - but has been known to break into the 30's on long flat roads.

me and fiero angel just drove my 3.4L 5 speed getrag car and her 3.4L 4 speed muncie (3:65 ratio) 70 miles, we filled up at the gas station, drove to meet saxman for lunch, then drove back home angie got 30.4 miles per gallon on her 4 speed car running 68-70MPH the whole trip, my 3.4L getrag 5 speed car got 35 miles per gallon exactly

oddly her trip meter was reading 69.8 miles and mine was 71.7 miles


hope that makes some people see that the v6 cars can get good mileage.

matthew

I averaged 30.5 with a headwind on my last roadtrip. [2.5 auto, 87SE] I was driving hills and curves so I was on the gas more than normal, with speeds running between 50-70 mph.

Just did a 240 mi. run mostly at 72-74 mph in my 88 GT and got 29.6 mpg. Around town or to work it gets 23-24.

quote Originally posted by Pyrthian: if you have a stock, or close to, 2.8 3.1 3.4 and you are getting under 20 MPG - or, more accurately - getting 15-17 MPG - the problem is your ECM is NOT going into "closed loop". this is when the ECM will use O2 sensor readings to adjust the fuel mix. the usual cause for this is the thermostat. the engine needs to reach a certain temp to go into closed loop mode. it also needs a good O2 sensor. the "open loop" mode dumps alot of fuel in the fuel air mix, and will get you roughly 15-17 MPG.

That's exactly what I get for mileage, 15-17mpg. Car had a 3.4 in it when I first got it, then it kept eating cams so I put a 2.8 in and the crank was gone so now I'm running a 3.1 and I get the same mileage.

I just got 30mpg on a highway trip with a bad fuel filter and a slightly dragging e-brake. Quick wot stint to 95, but mostly 70mph cruisin. I put a new filter in, and fixed the e-brake. I have no cat and no egr so my goal is 35mpg+ on the highway with my 5-speed V6.

My 85 se with 5sp 4 cyl averages 32 combined and 40 hwy...It once got 43 but to be honest i was drafting an 18 wheeler almost 100 miles up 29...That will really make mileage..

I just sold my 88 notch duke 5 speed.. driving like the penny piching skinflint scanning the ground for pennies that I am.I use this car as a daily driver for 3 years trouble free(ended when loan to friend) in light traffic with an S 10 head,cherry bomb ,no cat set up on the cheap for maximun MPG I got 28 to 32 around town often skiping a gear on shifts,, I was trying for over 40 mpg,at over 70mph I could not get this milage that I had modified car for!! at 60 to 67 mpg was phenomenal,, if a strong wind was pushing me then 45 mpg at over 70 was possible ONE time.. I even had vacuum gauge for hi speed runs.. With stock head I recieve 26 to 30 around town with normal shift pattern about 40 mpg at steady 65mph,, these were carefully conducted test using only accurate stock speedo and road maps and road signs with 215 pound driver (now 230) was dissapointed in cherry bomb mpg performance but seat of the pants dyno said yea baby sound was right on going thru the gears..flowmaster delivered same mpg as cherry bomb,cherry bomb mucho cheap tho

<

I want to build a ultra MPG ecotec fiero and try to get 50 on the highway but that is a few thousand dollars off haha.

For the first time since I bought my car (many months ago!) I now have a properly working 3sp automatic transmission (2nd gear was completely AWOL for a while), and EGR tube/system without leaks, so have been able to check my fuel consumption figures more accurately...

A recent trip to Le Mans and back showed (for part of the journey) 19 MPG at a steady 75 mph (over 2 hours), and 35 MPG at a steady 60 mph over 1.5 hours.

That's using an imperial gallon - with US gallons, the figures are 16 and 29 respectively.

Very pleased with the 60 figure, but not so pleased with the 75 figure. Still have some work to do, but it's the first time I've had some figures to work from.

Will have to connect up my laptop again and do a couple of runs.

Ciao!

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The Madscanner (85 SE 2M6)

[This message has been edited by Madscanner (edited 06-30-2008).]

Was at 20mpg; with tuneup, advanced timing two degrees, 2 lbs extra air in tires, now
getting 26 mpg combo city and freeway driving.
87 gt manual

I consistently get around 30 in town and 38-40 on the highway. It was great going to Fierorama from Dubuque Ia round trip on 1 tank of gas and could only squeeze 9 gallon in it on the fill up when I got home(about 350 miles). This is the first year I drove her all winter. I go a two full weeks on a tank of gas 225+ miles and it usually takes a little less than 8 gallons to fill up. I have my timing advanced about 2-3 degrees, and run a superlube (prolong, slick 50, or duralube) every 3rd oil change or so. Also run my tires about +5 psi. 2.5 liter auto 1985 sport coupe. 4 wheel alignment 1 year old; full suspension rebuild 2 years old; rebuilt engine 8500 miles with new head, 127000 on car; run ethanol blend. Did the Dells run round trip and the drive on less than 3/4 tank. Loved gunning the roundabout intersection. Now it is time to find out what old blue (86 sport coupe) and the fastback conversion can do (86 se 2.8) as soon as I get them up and running.

I have never checked mine in town, as I dont live in town. Onalaska is just 1 1/2 mile dfrom me, every thing else ,( Walmart), is more than 17 miles away. I get 38-41mpg driving my 2.5 base coupe w/ 5spd stick at and around 70 mph, I came back home from Galveston to Livingston this afternoon and onlt got 39mpg. It was 96* . It was 70* when I left this morning at 7:30am and I got 42mpg going down. I use a 195* thermostat and run 36lbs in all four tires. Dukes are designed to run hot, the 185*'s will cost you mileage. Sometimes I just skip 4th gear. My best was 42 mpg driving 60 mph for 3 hours. This was when I was breaking in my engine from 0 miles on a new rebuild.

Joe Crawford
Texas

1986 SE
City: 19mpg
Highway: 24mpg

ZZ4 V-8 with a 4-spd.

just ran my first tank of gas after my 7730 swap: 30.4 MPG
big jump for me - was getting just over 20 with my orriginal ECM w/ADS Superchip in it. yes, I know aftermarket chips wreck milage.
I tanked up early because I used to get roughly 160 miles to a tank. and I got to 150 miles on the new setup, and still had a 1/2 tank - and I thought my gas guage had gone bad thru the winter. NOPE. quite a chunk of happiness this 7730 is for me. this pops my Fiero form the worst MPG in my fleet to the best MPG in my fleet - which includes a Ford Escort which gets 27MPG.

My stock 86 coupe 4 cyl 5 speed gets about 28 mpg at best.

On road trips in the '88GT I get 31mpg.

My '85GT gets 19mpg city and 24mpg highway.

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RickN
White 88GT 5spd
White 85GT Auto
White 99 F250SD 7.3PSD 6spd
1956 Ford 860 Tractor w/ Freeman Loader

86 SE all oriinal - bone stock V6 w/4spd. Replaced the usual snsors, recent tune up, etc. 25 plus around town, 30 plus on the highway depending on where the gas pedal is pushed too.

Lets see my beat up little 88 Duke 5-speed got 33.5 MPG when I did the calculation last week. Not bad considering I drive about 1.5 hours each way to work every day.

88 GT with SBC/Ramjet PFI/Getrag
City: 15 to 17 depending on mood
Highway: 23

88 Coupe with 4.3 CPI/4T60
City: 25-28
Highway: hasn't been on a long trip yet

'88 2.5 auto Avg 30.87 last fill up! I drive it back and forth to the airport. 40 miles one way of which 14 is on the highway.

mine is projected to be about 35 mpg highway. pretty good for all the mods done. check my sig

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3500 LX9 from 06 Malibu, WOT-TECH.com 1280 grind stage 3 cam, LS6 valve springs, 1227730 ECM conversion, Darrel Morse solid aluminum cradle mounts, Truleo headers modified to fit the 3500, 36# inectors, 70mm 4.3 throttle body adapted to 3500 intake, ported heads, upper and lower intakes, lightly polished, WOT-TECH crank trigger wheel, CenterForce dual friction clutch, Flowtech Afterburner muffler, 2.5" piping, cat deleted, EGR deleted, SinisterPerformance tuning, C6 Corvette exhaust tips. projected to be 35 MPG with a guesstimate of 250 hp to the wheels

My 85 GT has avg'd aboot 23 mpg since ive been driving it this summer. (bought it at the end of 07 and i dont think i used a full tank before i put it away for the winter)
Best ive gotten has been 24.4 mpg w/ mixed driving.

Its the 2.8L 4 spd manual
no real mods...k&n air filter, Full ocelot exhaust...its running pretty rich right now too so thats not helping either.

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Romeoliquorstore.com
Myspace

My TCC is out on my 85' 2.8 auto, so it is getting 20-22mpg with mixed driving. It's getting that because of the 215/55/16 I put on to help raise the gear. I'm trying to get the parts I need to fix the problem now.

On my 88 5 speed 2.8 on the trip to the 25th in Michigan I averaged right around 30...not bad for a 20 year old motor. But maybe because I was also burning oil along with the gas?

I get about 21mpg with V6 and auto, mixed driving. i've also found that right after cleaning the air filter and inflating the tires i get best milage (25+mpg) aroung 55mph

quote Originally posted by josef644: I have never checked mine in town, as I dont live in town. Onalaska is just 1 1/2 mile dfrom me, every thing else ,( Walmart), is more than 17 miles away. I get 38-41mpg driving my 2.5 base coupe w/ 5spd stick at and around 70 mph, I came back home from Galveston to Livingston this afternoon and onlt got 39mpg. It was 96* . It was 70* when I left this morning at 7:30am and I got 42mpg going down. I use a 195* thermostat and run 36lbs in all four tires. Dukes are designed to run hot, the 185*'s will cost you mileage. Sometimes I just skip 4th gear. My best was 42 mpg driving 60 mph for 3 hours. This was when I was breaking in my engine from 0 miles on a new rebuild. Joe Crawford Texas

After a trip to Dallas and back I only averaged 38 MPG driving 72MPH with the AC on. Maybe I need a tune up?
Joe

driving like a grandma i got 23 in my 85auto v6 2.8
but normal drivng got around15 maybe 12 but i have an electrical problem
whith the o2 sensor egr and hundreds of others just goin out
maybe if i just run so fast that the fuel pump cant keep up it will stop running so rich

quote Originally posted by 2farnorth: I don't know why yet, but my 86 GT 4 speed gets better mileage than my 86 coupe 4cyl auto. When I first started driving the coupe it was getting 27-28 around town. Now I'm lucky to get 23. I think part of it is the current blend of gas. The change started about the time they started putting the ethanol in the gas. Might be a coincedence, but I doubt it.

Wow this is an old thread... My 86 4 cyl auto coupe is back up to 29 in mixed driving. I've changed the cat, dist cap, ignition wires, and the egr valve. I did have an 85 SE V6 Auto with air that would get 24 around town and 32 to 34 on the highway depending on what speed I drove. Should've never sold that car.

im kinda thinking of getting a duke fiero since they do rock out some monster milage. and i want to drive another fiero when i cant be driving the GT.

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1987 Fiero GT built by my brother, merlot566jka, 3500 LX9 from 06 Malibu, WOT-TECH.com 1280 grind stage 3 cam, LS6 valve springs, 1227730 ECM conversion, Darrel Morse solid aluminum cradle mounts, Truleo headers modified to fit the 3500, 36# inectors, 70mm 4.3 throttle body adapted to 3500 intake, ported heads, upper and lower intakes, lightly polished, tcemotorsports.com crank trigger wheel, CenterForce dual friction clutch, Flowtech Afterburner muffler, 2.5" piping, cat deleted, EGR deleted, SinisterPerformance tuning, C6 Corvette exhaust tips. projected to be 35 MPG with a guesstimate of 250 hp to the wheels

pure highway, no stops 24 mpg. Pure city driving 9-12, mixed average 15. Good times