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1985 Pontiac Fiero Gas Mileage Log and Handbook by disjaukifa
Started on: 07-05-2013 01:56 PM
Replies: 9 (759 views)
Last post by: armos on 07-11-2013 08:19 PM
disjaukifa
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Report this Post07-05-2013 01:56 PM Click Here to See the Profile for disjaukifaClick Here to Email disjaukifaSend a Private Message to disjaukifaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hey Guys,

I'm new here but I keep reading conflicting reports about the gas mileage about the Fieros. While I can't report on all Fieros I can document what I currently get in the car, and comment on if modifications to the Fiero helped with gas mileage or not. Here is what I'm starting with, a bone stock 1985 Pontiac Fiero 2m4 2.5L iron duke with a 5-speed manual transmission.

Currently I have down two fill ups:

1st tank: 28.6mpg (50/50 city/highway) Also this was my first tank so I played with it a lot
2nd tank: 29.0 mpg (70/30 city/highway) Still played with it a lot

Currently the Fiero is getting new timing gears installed but I have changed the following:

New MSD Coil
Platinum spark plugs
8mm spark plug wires
Cleaned and oiled K&N air filter
Timing (I'm going to start out with it set to 10 degrees)
Replaced worn v-belt on water pump/alternator
5w-30 Synthetic oil instead of the 10w-30 conventional oil
New Oil Pump

Now the tank that is currently in it that is almost empty was almost pure highway but I haven't had a chance to mess with it yet so I don't know what the mileage will be, hoping 31 ~ 32 mpg. The 4th tank is the one that I'm curious about because it will have the above modification done to it. Thinking about switching to premium gasoline because I've heard that it will increase the gas mileage as well.

Possible future modification I'm thinking about applying to increase gas mileage:

Short-term:
Premium Gasoline
Advance Timing to 12 degrees
Increase tire pressure (I have it set to about 32 psi but the tires limit is 35, so I'll set it to 35psi)
Wrapping the exhaust to lower engine bay temperatures (probably won't make a difference)
Replace worn out Struts and Shocks

Midterm:
Holley 500-1 300cfm replacement TBI (I'm actively looking for one if you have one please let me know)
Install Cruise Control (modern universal control unit using the stock Pontiac Fiero Cruise Control stock)
5w-20 Synthetic Oil (If the pressures look good running 5w-30)

Long-term:
New tires
Stainless steel exhaust system
Tuning of the ECU
Possible look at a lightweight rim option for the Fiero
Holley intake manifold

Again I want this thread to document my real world results for my gas mileage in my 1985 Fiero. I'm curious to see how the changes I make help/hurt my fuel economy. Also I do not baby a car, this car is meant for handling and as such I will still be driving into the corners for fun etc, I won't baby the car all day long.

Thanks
Grant

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masospaghetti
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Report this Post07-05-2013 02:24 PM Click Here to See the Profile for masospaghettiClick Here to Email masospaghettiSend a Private Message to masospaghettiEdit/Delete MessageReply w/QuoteDirect Link to This Post
Just my 2 cents.

- A drop-in K&N filter usually flows worse than a stock filter because they have less actual surface area. The pleats are shallower. This may not be true if you use a cone type filter.

- Header wrap generally results in rapid corrosion of the header. Condensation forms when the header cools after you turn off the engine and it gets trapped in the header wrap material. It would be much better to use a ceramic coating. They make a ceramic paint you can buy at the store (VHT paint) but I don't know how effective it is.

Have you considered LED lamps for the rear and marker lamps? They will save a bit of power and therefore improve fuel economy. Be careful though, you have to get pretty good ones for them to be bright enough. I got some of those tower-type "SMD" bulbs and they seem at least as bright as original.

Also you may consider putting in synthetic oil for the transmission. Amsoil makes a synchromesh (5w-30 weight), so does Redline oil. Both are full synthetics.
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disjaukifa
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Report this Post07-05-2013 02:31 PM Click Here to See the Profile for disjaukifaClick Here to Email disjaukifaSend a Private Message to disjaukifaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by masospaghetti:

Just my 2 cents.

- A drop-in K&N filter usually flows worse than a stock filter because they have less actual surface area. The pleats are shallower. This may not be true if you use a cone type filter.

- Header wrap generally results in rapid corrosion of the header. Condensation forms when the header cools after you turn off the engine and it gets trapped in the header wrap material. It would be much better to use a ceramic coating. They make a ceramic paint you can buy at the store (VHT paint) but I don't know how effective it is.

Have you considered LED lamps for the rear and marker lamps? They will save a bit of power and therefore improve fuel economy. Be careful though, you have to get pretty good ones for them to be bright enough. I got some of those tower-type "SMD" bulbs and they seem at least as bright as original.

Also you may consider putting in synthetic oil for the transmission. Amsoil makes a synchromesh (5w-30 weight), so does Redline oil. Both are full synthetics.


I should have said that the car came with the K&N air filter, it wasn't something I bought, I just cleaned it and re-oiled it.

I have thought about replacing most of the lighting bulbs in the car with LEDs but not for gas mileage, more for heat/power savings, its something that I need to add to the list!

Also that is great information about the transmission fluid, I had never thought about replacing the fluid in the manual transmission, never had to before . . . that is something I need to investigate as well!

Yeah I'm not completely sure what I'm going to do on the exhaust yet, I want to cool the engine bay down somehow, just haven't figure out how to do that yet!

-Grant

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armos
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Report this Post07-06-2013 10:50 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by disjaukifa:
I want to cool the engine bay down somehow, just haven't figure out how to do that yet!

For the purposes of longevity, I like to use a different fan switch which will turn on the radiator fan at 210F. This reduces the worst case temperatures in the engine bay, but I don't think it would do any good for fuel mileage. I don't know if the same fan switch is compatible with 4cyl cars.

To get repeatable results, it would be best to do your measurements with cruise control on a consistent route with consistent speeds selected over the whole trip. Aggressive driving and different routes introduce too much randomness.
Manual control of the throttle might give you better mileage than cruise control. But I still think cruise is better for repeatability when you're experimenting with other tweaks. You can count on the cruise to behave the same every day.

One of the best bargains that improved my mileage was replacing the O2 sensor. Denso is generally recommended, not Bosch. They age gradually, but they don't give an error code until they're completely dead.
Premium fuel might increase your mileage to the extent that it allows you to advance the timing. What I'd do is figure out how far you can safely set the timing on regular, get mileage from that, then see where you can set it with premium and measure again.

It might do some good to have the injector cleaned and refurbished, but I don't know what that costs for a TBI injector or how often they develop problems. You could try watching the injector spray pattern by using a timing light. If you see any problems it may be worth doing something about.
Look for any possible vacuum leaks also.
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disjaukifa
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Report this Post07-10-2013 04:40 PM Click Here to See the Profile for disjaukifaClick Here to Email disjaukifaSend a Private Message to disjaukifaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by armos:

For the purposes of longevity, I like to use a different fan switch which will turn on the radiator fan at 210F. This reduces the worst case temperatures in the engine bay, but I don't think it would do any good for fuel mileage. I don't know if the same fan switch is compatible with 4cyl cars.

To get repeatable results, it would be best to do your measurements with cruise control on a consistent route with consistent speeds selected over the whole trip. Aggressive driving and different routes introduce too much randomness.
Manual control of the throttle might give you better mileage than cruise control. But I still think cruise is better for repeatability when you're experimenting with other tweaks. You can count on the cruise to behave the same every day.

One of the best bargains that improved my mileage was replacing the O2 sensor. Denso is generally recommended, not Bosch. They age gradually, but they don't give an error code until they're completely dead.
Premium fuel might increase your mileage to the extent that it allows you to advance the timing. What I'd do is figure out how far you can safely set the timing on regular, get mileage from that, then see where you can set it with premium and measure again.

It might do some good to have the injector cleaned and refurbished, but I don't know what that costs for a TBI injector or how often they develop problems. You could try watching the injector spray pattern by using a timing light. If you see any problems it may be worth doing something about.
Look for any possible vacuum leaks also.


Thank you for the advice! I currently don't have cruise control on the car so that is something I'm wanting to add, because as you said it will take out the human error out of it as well. Still trying to get the car back together, because of timing gear issue, which it wasn't but that is a different topic!

I'm going to rebuild the TBI myself and I can go ahead a replace the O2 sensor as well, I hadn't even thought to see how the one on my Fiero even looks right now so that could help my gas mileage as well!

Thanks
Grant
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Report this Post07-11-2013 04:54 AM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
Actually, higher octane fuel will probably reduce your fuel economy, unless you tune for it.
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disjaukifa
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Report this Post07-11-2013 08:54 AM Click Here to See the Profile for disjaukifaClick Here to Email disjaukifaSend a Private Message to disjaukifaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Blacktree:

Actually, higher octane fuel will probably reduce your fuel economy, unless you tune for it.


I will be tuning for it honestly. At some point I'll be taking the ECM out and seeing if I can mess with the programming of it like I can with my 88' C1500.
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Report this Post07-11-2013 01:05 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
I've heard on some of the car programs on TV that penny for penny, the gain with premium fuel is of no benefit to a car designed to run on regular, other than it won't harm the rubber components of the fuel system on older cars.

You can replace the Isuzu transmission fluid with PennZoil manual transmission synchromesh fluid. It is on the shelf at most AutoZone stores. It's a synthetic and it's the same identical fluid that GM sells at a much higher price. Two and a half quarts will do the trick after a complete drain. Remove the VSS very, very, very slowly and deliberately to avoid dropping the gear back into the transmission.

You may encounter ignition module failures after installing the MSD coil. There's mixed opinions on that with some having no problems while others found that ignition module failures went away after changing back to the original stock coil.

Spark plugs should be the original recommended AC Delco number plugs. The Fieros do not like fancy plugs like twin fire, platinum, and others.

Like Armos said, the 210 fan switch is a good idea. The Duke is less forgiving of overheating than the V6's so if you can get the fan to kick on earlier, the better for the engine. I'm not a big fan of the ultra low temp switches because they tend to keep the engine below operating temp, so fuel mileage suffers, and that would defeat your intent.
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Report this Post07-11-2013 04:29 PM Click Here to See the Profile for edfieroClick Here to Email edfieroSend a Private Message to edfieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
premium fuel will not increase mileage.

new TBI also wont help. I had tried running the one in my 84 that the Fiero Store use to sell a few years back....no performance gain, slight mpg loss...plus it caused the car to run rough and back fire some times.

new 02 is good idea.

more timing will help performance a bit, but may hurt mileage.
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Report this Post07-11-2013 08:19 PM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post
Premium is something I've always wanted to experiment with, but my car and driving route haven't been stable enough to allow a good comparison. With the same timing I expect it wouldn't help (might even hurt slightly) but with more timing, maybe it would. Conventional wisdom says it's not worth it - and it's probably not - but it's something I'd still be interested to experiment with and measure. If you have a good opportunity to compare, with corresponding timing adjustments, I'd say go for it.
When I had an 84, I used to use 89 octane in it just because I liked how it ran with more advanced timing. I don't know what that change did to mileage, I didn't care back then.
I'd also like to experiment with thermostats sometime.
I'm getting interested in tuning the deceleration fuel cutoff behavior of the ECM, because datalogging has shown it's so rarely invoked that it's pathetic. I live in a hilly area and think I should be seeing it work far more than I do.
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