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Old 02-03-2009, 05:28 PM   #1 (permalink)
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Fiona - '84 Pontiac Fiero
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Getting good mpg from my Fiero

I have a 1984 Pontiac Fiero that i have been working on to get some good mpg numbers from. My last tank wasn't that great for some reason. I went 175 miles on 7.4 gallons, which equates out to 23.5 mpg. To me, this is horrible. I had installed my vacuum gauge about halfway through my last tank. Towards the end of my tank i took off my antenna, and covered my directional holes with Plexiglas. I do not think it will make that much difference, but why not right?

Right now i have snow tires on the rear, which are pretty tall. I also have 100 pounds of weight in the front because i need weight up there to track well in the snow. All 4 tires are all up to pressure.

Last summer i achieved 37mpg on the highway, being very easy to not go too fast. I did some drafting of some big rigs to achieve this haha.

Because it is winter, i let my car idle for a few minutes before i leave for school. Does anyone think that this could make that much of a difference?

In the Summer my all around mpg was 28ish.

Anyone have any ideas? lol
Thanks in advance

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Old 02-04-2009, 12:17 AM   #2 (permalink)
amateur mech. engineer
 
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Sporty Accord - '88 Honda Accord LX-i
90 day: 23.25 mpg (US)

Dad's Camry - '01 Toyota Camry CE
90 day: 22.81 mpg (US)

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Your mpg is about the same as mine. I have a smaller engine but you have a manual transmission. I don't think your fuel economy is especially bad for short trips in cold weather.

Eliminating the warm up time would be helpful. If you accelerate gently during the first five minutes, you are not likely to hurt anything.

Probably the easiest modification to try is advancing the ignition timing a little. It's best if you have a timing light for this adjustment. Maybe you could borrow one from an auto parts store like Pep Boys or Autozone if you don't have one. It would be a good idea to check the repair manual for your car to understand the procedure. Mark the original distributor position with paint or a scratch before moving it. Keep it close to the recommended timing. I would avoid anything more than 4 degrees advanced from the standard setting. If it starts knocking, retard the timing a little (like 2 degrees) and test again. I'm not sure if your engine uses a distributor. If not, ignition timing adjustments may not be possible.

Check brake drag and wheel alignment since these can increase rolling resistance. Check if you can easily push your car on a level paved surface. If not, something may be wrong. If you lift wheels off the ground with a jack, you can check how easily they turn. Be sure to block wheels still on the ground with sticks, stones or other objects to avoid an accident.

One easy way to check wheel alignment is to drive forward, stop and measure how much a front tire sticks out horizontally past the rim, then drive backward, stop and measure again. If there is much difference (like over 1/8 inch) then an adjustment should reduce the drag. On cars that have independent rear suspension (like yours), it is useful to do the same measurement on the rear wheels too. Toe in causes the tire to move in (towards from the center of the car) when driving forward and toe out causes it to move out.

Avoiding snow tires will reduce rolling resistance. Remove them early when winter is over. If they are taller than the original tires, they might make your measured mileage less than your actual mileage. You might be getting better fuel economy than you think you are.

If you have a voltmeter you may be able to test all the electrical sensors that send information to the computer. Bad sensors usually increase fuel consumption.

Since your car is getting old, check all the vacuum hoses to see if any are hardened, cracked or collapsed.

Using a low viscosity synthetic engine oil and transmission oil should help reduce friction in cold weather.

Be sure to check the "65+ Efficiency Mods" at the top of the page.

Last edited by Andyman; 02-04-2009 at 12:27 AM.. Reason: missing word
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Old 02-04-2009, 12:37 AM   #3 (permalink)
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wow, that was a very informative post
Quote:
Originally Posted by Andyman View Post
Avoiding snow tires will reduce rolling resistance. Remove them early when winter is over. If they are taller than the original tires, they might make your measured mileage less than your actual mileage. You might be getting better fuel economy than you think you are.
I was thinking about that. The car was originally designed with smaller tires; therefore, the odometer is adjusted for these tires. It is very possible that these tires are a reason for the low odometer reading. Hmm...something to look into.

Thanks for the help. You have me some good ideas on what i can look into. Much appreciated!!

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