list it.

Very consistent 21.5 MPG mostly driving for fuel economy, split between 55 MPH country roads and sorta-city driving (not stop-n-go, more like stop every once in a while if out of sync with the lights). On an 88 5-speed duke. I feel that either my EGR or O2 sensor, or both, are ruined, since people consistently get better numbers with 2.8's.

------------------
1988 Metallic Red Pontiac Fiero CJB T-Top Coupe, # 784 of 1252

Check your plugs, and or coil packs. The 88 duke ignition is very sensitive, it likes regular plugs and good working coils.

Same setup here 100 miles daily, average about 30-35 usually on the higher side, as soon as it drops below 30 I start looking into things. First place I start is plugs, the cheapies work great!

Yeah I would definitely check out your engine as I'm average about 31-33ish mpg with a decent mix of city/highway. Mine is also a '88 5-speed 2.5

------------------

1995 Pontiac Firebird - 3.4 V6 5-Speed (Engine outta commission awaiting V8/6-Speed swap someday), 93-97 to 98-02 Trans Am body conversion My Firebird's Cardomain Page
1988 Pontiac Fiero - 2.5 I4 5-Speed My Fiero's Cardomain Page

I just got back from a 3500 mile drive where I averaged almost 37 mpg- I usually get 32-34 on the highway and never less than 31.
Stock '88 duke 5-speed with 118,000 miles.
In my '87 duke (also stock with about the same miles) I get 29-31, but it is definitely not running perfect, and it smokes a little.
If you are only getting 20 mpg, there is something seriously wrong, and I don't think it is just plugs.

88 Formula - 2.8/5 spd - all stock with cat. Averages 27.6 on the interstate @ 80 plus. Averages 31 @ 65 to 70. around 24/25 in town - traffic - stop and go.

88 Coupe - Duke with auto - would get close to 33 on the interstate 65 and below - over 65 28 and less as speed increased. 23/24 around town. Now has a 4.9 with the 4T60E auto and is getting 23/24 around town but I just found out that it's only getting about 1/2 the pressure it needs so it's been running lean! It will most likely drop to 20/21 aaround town with the proper fuel pressure.

86 Coupe with a carbed 350 SBC / Econo 4 spd. It gets about 16 driving easy - 12 or less light to light!

2200 5 speed, last time I checked I was getting 24 mpg. I need to get the thermostat installed and see if that helps. But my other cars get 9 mpg so its pretty nice when I drive it.

[This message has been edited by Jake_Dragon (edited 06-13-2010).]

23MPG 85 GT stock 2.8 4 spd (only mod is the ocelot exh from the Fiero Store)
Mostly highway driving. I'm Cleaning up the engine now and replacing the ignition components among other things. Should help performance, maybe mileage too.

[This message has been edited by Dougie Murder (edited 06-14-2010).]

14-18.....Its how I drive....2.8 auto

18/23
Six spd
Worked over LT1

25-27 mpg 50/50 hiway and city dirving. 3.4 PR with Getrag.

It's my daily driver.

20mpg's on a stock 2.8 with an auto. Has all kinds of things wrong with it right now, so I'm surprised it even gets that. Mostly highway typically doing 65 - 70 to work.

3800 turbo automatic

E85 18/25
E10 28/38

quote Originally posted by N3M3S1S: 20mpg's on a stock 2.8 with an auto. Has all kinds of things wrong with it right now, so I'm surprised it even gets that. Mostly highway typically doing 65 - 70 to work.

Thats not bad, I was getting 18 with the same engine and a 4 speed. I have a lead foot

quote Originally posted by Jake_Dragon: Thats not bad, I was getting 18 with the same engine and a 4 speed. I have a lead foot

Yeah? Back in its lower mileage days it got about 25. Right now it needs the egr tube, o2 sensor, and tjuneup items replaced. It's also running pig rich right now, I almost get a high sitting at idle with my windows open. Gotta figure that one out. Also my brakes are spongy as hell. All in all I've been neglecting the poor girl due to a chaotic past couple months. =/

On Dell's run got about 34 in my 85 2.5 coupe auto with a 35 mph head wind. Typically get 38 highway and 28-30 city. Have seen as high as 40 highway.

2.8/Isuzu: 25-28 on daily commute, up to 32 on steady 75mph.

4.3/4T60: 24-27 on daily commute, up to 32 on steady 75mph.

SBC/Getrag: 15-17 on daily commute, up to 22 on steady 75mph.

Well, I don't think anyone believed me but, I had a 88 Coupe, 5 speed car, A/C delete that I could get 45+ mpg on highway trips driving 55 to 58 mph. Steady state driving over long distances. That coupe now has a 3.4 with the same Isuzu manual in it. I haven't checked the fuel efficiency yet but I expect to get mid thirties.

Ron

88GT 2.8 5spd MSD Ignition, New Injectors, Ported everything. (Heads, Exhaust, Throttle Body, Intake Manifold) Mild Cam, decked heads to increase compression.

Now this one is a hard one for people to believe, however everyone in the local club saw it and saw me driving, on our last major club run, I averaged 90mph, with trips to 121mph, towing a trailer. (Video and Pics to prove it) I averaged 30mpg.

Running empty with just me in the car on steady highway I routinely get 30-34mpg.

In town with a lead foot and lots of trips to 5000-6000rpms usually results in a respectable 25-28mpg.

This is probably the best running 2.8 I have ever owned. I have had 4 or 5 different 2.8's and for some odd reason, this one is great on gas, performance is above average. Here in BC where our gas prices are usually pushing $5 per gallon, we do all we can to keep our engines in top running condition.

------------------
85GT Soon to be 87GT,93 Eldorado 4.9, 5spd Dual O2 Custom Chip, Custom Exhaust. MSD Everything Capt Fiero --- My Over View Cadero Pics Yellow 88GT 5spd Full Poly Suspension, Lowered 1/2" in front, Corner Carver.

27.8MPG all highway at about 70MPH... 1988 GT 3spd Auto... on the way to the Dells... must have been some good gas.

88 Formula.
LQ1 mated to a 5spd getrag.
25.67MPG last tank, driving like a shithead. I will update after I fill up later today, if I get the car out.

84 SE 2.5/4 speed about 6 mpg city/highway. Lowest was 4, highest was 9. I really need to figure out what is wrong with it.

[This message has been edited by topher_time (edited 06-15-2010).]

quote Originally posted by topher_time: 84 SE 2.5/4 speed about 6 mpg city/highway. Lowest was 4, highest was 9. I really need to figure out what is wrong with it.

Possibly a hole in the petrol tank

3.0 Superduty 4 cyl / Getrag 5-speed 11-25 mpg depending on the weight of foot

------------------

Interesting this just came up; as I was wondering waht the heck is wrong with my MPG!

First, I have an 88GT manual
Brand new rebuild, everything new (still under 500 miles)
Stroked to 3.1L
272 cam
FPR set to 45psi
Total seal rings
Port/polish intake/exhaust
no cat - straight pipe
Stock muffler
NO CODES, runs fine and idles nice. But has a slight miss off idle

I am getting around 12mpg!
Duno what I am getting now, as I just installed a cat because I did not like the raw fuel smell and the excess noise...

My 1985 SE with a TBI Caddy 4.5/ 4t60 gets 22~24 MPG in town and a little over 30 on the highway.

quote Originally posted by ALJR: Interesting this just came up; as I was wondering waht the heck is wrong with my MPG! First, I have an 88GT manual Brand new rebuild, everything new (still under 500 miles) Stroked to 3.1L 272 cam FPR set to 45psi Total seal rings Port/polish intake/exhaust no cat - straight pipe Stock muffler NO CODES, runs fine and idles nice. But has a slight miss off idle I am getting around 12mpg! Duno what I am getting now, as I just installed a cat because I did not like the raw fuel smell and the excess noise...

Be prepared to replace the CAT again soon if you are getting 12 mpg and have raw gas smell out the pipes...

<<

quote Originally posted by FieroMonkey: Be prepared to replace the CAT again soon if you are getting 12 mpg and have raw gas smell out the pipes...

Raw gas smell was before the cat was installed. I do not smell it now...
Should I be worried still? What would cause it?

quote Originally posted by ALJR: Raw gas smell was before the cat was installed. I do not smell it now... Should I be worried still? What would cause it?

I would still be concerned about it. You haven't fixed the problem. You've just masked it. A fuel smell that was "fixed" with a new cat would be a result of running too rich, which could be caused by an exhaust leak upstream of the O2 sensor (cracked manifold(s) or blown manifold gasket), a bad sensor, and probably a few other things I haven't thought of.

26-28 mpg with 3800SC and 4t65e HD. My lead foot has something to so with not getting better mileage.

quote Originally posted by Formula Owner: I would still be concerned about it. You haven't fixed the problem. You've just masked it. A fuel smell that was "fixed" with a new cat would be a result of running too rich, which could be caused by an exhaust leak upstream of the O2 sensor (cracked manifold(s) or blown manifold gasket), a bad sensor, and probably a few other things I haven't thought of.

No crackes anywhere. Manifolds were ported then welded. Very quiet in the engine bay (aside from the roller-rocker sewing machine noise)...
I would have to imagine if I had a bad sensor, I would see a code of some sort?

Thinking I should start a new topic in the tech section for this...

88 GT 5-speed, bone stock except for K&N filter. Using the A/C all the time (west Texas) and a combo of in town and freeway driving I average 27-28 mpg.

[This message has been edited by Rick 88 (edited 06-17-2010).]

AJLR- dunno if this is the issue but if you are using different injectors with higher fuel pressure it could cause the rich condition you seem to be experiencing.

I think factory is like 42, and if you are using the multec style injectors vs the pintile style, I have seen them go rich at idle, and added fuel pressure might just exacerbate the situation.

18-22 city, 27-29 HWY @ 70mph. 4.9/getrag with 25.7" diameter rear tires. Still have an issue with the MAT tables in the PCM. Hoping to get a little more once thats fixed.

14 city/24 highway with a 84 fiero / used up old 1983 crossfire 305/ 4t60 ( 2.84 rear). car with out driver is 2988 pounds on the scca 4 cornner scales.

quote Originally posted by jgrotzin: AJLR- dunno if this is the issue but if you are using different injectors with higher fuel pressure it could cause the rich condition you seem to be experiencing. I think factory is like 42, and if you are using the multec style injectors vs the pintile style, I have seen them go rich at idle, and added fuel pressure might just exacerbate the situation.

Thanks for the info!
I am running the stock 2.8 injectors, that is why I bumped the PSI up a bit (for the 3.1 displacement)...

I have been tracking my 87 GT Auto mileage since last Dec. The best I had ever achieved was 21.4 of highway driving. I had noticed a progressively worse vibration at the rear of the car at 60+ mph and had assumed it was due to a failing motor mount. The P.O. of this car had replace the two rear tires with Goodyear Eagle GT's a few years ago and they were quite weather checked and mismatched to the fronts. So I decided t replace a four with Bridgestone Potenzas until I upgrade my wheels and tires to 18" sizes. Having driven 1000+ miles since the new tires my mileage jumped to 24.5 and the last 2 days I completed a 600 mile trip at 75 mph highway driving and averaged 25.6 on the last tank or fuel. I am amazed that tire choice made that big of a difference not to mention how much quieter the ride is. On the negative side I now realize how bad my exhaust system is and it will need to be replaced very soon.

29/30 mpg on the highway, steady 70/75 mph, stock set up.

------------------
1988 GT
Manual
Medium Red Metallic
Gray Leather

0 Mi/Gal, my fiero currently has no engine
Anyone know average milage for a Northstar/5speed combo?