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
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11:12 PM
jgrotzin Member
Posts: 349 From: Rocheport, MO Registered: Nov 2005
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!
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.
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12:57 AM
katatak Member
Posts: 7136 From: Omaha, NE USA Registered: Apr 2008
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).]
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04:43 AM
87antuzzi Member
Posts: 11151 From: Surrounded by corn. Registered: Feb 2009
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.
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11:06 AM
darkhorizon Member
Posts: 12279 From: Flint Michigan Registered: Jan 2006
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
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. =/
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
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10:24 PM
Capt Fiero Member
Posts: 7657 From: British Columbia, Canada Registered: Feb 2000
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.
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...
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...
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05:54 PM
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
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.
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08:45 AM
starlightcoupe Member
Posts: 1767 From: Third World Country, OR Registered: Oct 2009
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...
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10:47 AM
Rick 88 Member
Posts: 3914 From: El Paso, TX. Registered: Aug 2001
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).]
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12:55 PM
jgrotzin Member
Posts: 349 From: Rocheport, MO Registered: Nov 2005
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.
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01:55 PM
Fieroseverywhere Member
Posts: 4242 From: Gresham, Oregon USA Registered: Mar 2006
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.
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07:20 PM
FFIEROFRED Member
Posts: 751 From: GULFPORT, MS Registered: May 2008
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.
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)...
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10:06 AM
infinitewill Member
Posts: 2345 From: Overland Park, KS U.S.A. Registered: Mar 2009
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.
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10:22 AM
Vernon8360 Member
Posts: 1106 From: Pittsburgh, PA Registered: Feb 2008