bad gas mileage?
Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=2161
Printed Date: 24 April 2025 at 11:17pm
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Topic: bad gas mileage?
Posted By: rumonk
Subject: bad gas mileage?
Date Posted: 05 November 2010 at 7:14pm
| my '84 w/ auto seems to have really bad mileage since i started driving it in april. i'm lucky if i get 160-180 kms to a tank, i realized the gas tank is small but it seems really bad. i have replaced the distributer cap and rotor, new plugs, new wires, i also replaced all the filters, o2 sensor, temp sensors, even replaced the injector but still no change, i have checked the timing and it's right on the mark. i just picked up a 3.8 v6 this week to do an engine swap, but i'm not planning on starting that until after christmas. i'm hoping to figure out this problem without spending to much money, any ideas would help. |
Replies:
Posted By: Patrick
Date Posted: 05 November 2010 at 7:29pm
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Did you check the timing with the ALDL jumpered? Have you done a compression test? Is this the engine you bought in a wrecked Fiero and mentioned http://www.westcoastfieros.com/forum/forum_posts.asp?TID=1733&KW - Here ?
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rumonk wrote:Posted By: rumonk
Date Posted: 05 November 2010 at 7:52pm
| it is the same one, i haven't checked the compression yet, i was planning on doing that this weekend, i did have it jumpered when i did the timing. the engine runs quite good, hasn't burnt a drop of oil. it just seems to be running really rich. |
Posted By: Patrick
Date Posted: 05 November 2010 at 8:57pm
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Have you checked to make sure the brake calipers aren't dragging? Cat isn't plugged? Functional 195F thermostat installed?
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Posted By: Capt Fiero
Date Posted: 05 November 2010 at 10:51pm
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Bump the timing 2 degree's over stock. That should improve gas mileage by 10% or more. ------------- Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd. |
Posted By: Romeo
Date Posted: 05 November 2010 at 11:52pm
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Does the exhaust smell rich? If not, problem would likely be outside engine condition. ------------- Never shift into reverse without a back-up plan. |
Posted By: rumonk
Date Posted: 06 November 2010 at 1:11pm
| the cat has been removed, i have installed a new thermostat, the exhaust does smell rich, i'll try to bump up the timing to see if it helps. i've also got to do the rear brakes this week so i'm planning on rebuilding the calipers anyways. thanks. |
Posted By: Patrick
Date Posted: 06 November 2010 at 1:24pm
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What temperature? 195 is best. 180 is okay. 160 is no good.
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Posted By: Romeo
Date Posted: 07 November 2010 at 12:24pm
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Your best bet, if you can, is to hook it up to a scan tool and see what the engine is doing. That will tell you what to look for, or at least point you in the right direction. ------------- Never shift into reverse without a back-up plan. |
Posted By: kharmata
Date Posted: 08 November 2010 at 12:25pm
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May I ask what sort of driving was done for when this low
mileage occurred? FYI. I too have had terrible gas mileage and thought something was wrong - even when i tried to drive like gramma (without getting run over in the process) but then i realized i am used to driving country roads with very little stop and go. So a little experiment over the weekend proved that I can still get close to 100km on a 1/4 tank of fuel (mostly higway - at posted speed limits near 90km/h. 
Cheers |
Posted By: Patrick
Date Posted: 08 November 2010 at 1:10pm
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No way. I cannot believe that a V6 Fiero would be capable of travelling 400km on a single tank of gas. I doubt that most (any?) duke powered Fieros could even achieve that. No way Kevin, no way!
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Posted By: Capt Fiero
Date Posted: 08 November 2010 at 1:59pm
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LOL Patrick, my 88GT will do 520kms on a tank, and there are 87 5sdp Dukes that can get close to 700kms on a tank of Freeway driving. I have heard people claim to get 40mpg out of a duke which would equal about 700kms. My 88 on several Trips to Oregon can get 30mpg. Heck you saw my Arlington Fill up towing a trailer and got IIRC 29mpg with an average crusing speed of 130kph. Special note, this is basing on the larger 87/88 tank on an 11 gallon average fill up from Empty. ------------- Capt Fiero 88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd. |
Posted By: Patrick
Date Posted: 08 November 2010 at 3:01pm
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All I can can say then is that there must be someone siphoning the gas out of both my GT's and my 84's tank, even while I'm driving.
EDIT: Okay okay, who's the smart guy with "mod" status who edited my statement above?
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Posted By: Colby
Date Posted: 08 November 2010 at 3:03pm
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I know I can get at least 35mpg on the highway with my Duke. Unfortunately my trips tend to be really short (<15 mins) with lots of stopping so I typically get closer to 23mpg, filling around 330km. So 400kms in a Duke should be easy.
------------- 88 Formula 5 speed |
Posted By: Patrick
Date Posted: 08 November 2010 at 3:12pm
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I'm curious how you guys actually work out your MPG, considering we buy our gas in litres and drive kms. Seriously, how do you do it? I have my own method and I want to see if my pathetic MPG works out the same with whatever method you guys use.
EDIT: Okay okay, who's the smart guy with "mod" status who edited this post as well?
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Posted By: Colby
Date Posted: 08 November 2010 at 3:46pm
Fill up, reset trip odometer, drive. Fill up again, write down kms travelled and litres used. Convert kms to miles, litres to gallons and divide miles by gallons. To convert quickly, just go to Google and search "300km to miles" etc. ------------- 88 Formula 5 speed |
Posted By: kharmata
Date Posted: 08 November 2010 at 4:12pm
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Sorry I did not do a direct fill then drive then fill again
- At the end of my hwy trip (when the needle was about 3/4 tank and km said 95) I got stuck on Alex fraser bridge for 10 min of stop go stop go  ....so i did not bother
anymore. Will try again soon. 
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Posted By: kharmata
Date Posted: 08 November 2010 at 4:14pm
No way.
No way Kevin, no way!
Thanks for the laugh Patrick - I could almost picture you stomping your feet on my monitor. LOL! |