Mysterious Drop In Gas Mileage

A friend of mine had some work done on his 1989 Ford Bronco in August, and the gas mileage plummeted. On his behalf, I'm asking for advice on what to do about it. Here is the information he gave me...
1989 Ford Bronco ... V-8 350 engine ... 250,000 miles ... 28 gallon tank and 380-430 miles to a tank depending on the weather ... live 3000 feet above sea level.
April 2006--fuel system cleaning -- tech code 15; and also 8 cylinder tune-up. Car ran well with usual gas mileage.
August 2006--car stopped running -- tech code 15 -- replaced 8 fuel injectors (MP 10898 Reman Fuel Injectors, 1 plenum gasket, 8 spark plugs, and 1 fuel press regulator).
The car continued to run well but gas mileage immediately reduced to 320 miles per tank maximum.
Went back to mechanic twice and he could not determine why the gas mileage has dropped so significantly.
That's the question. If you can help with an online answer that would be great. Thanks--Steve
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fodr dos not have a 350 engine. what is tech code 15?? is he measuring fuel mileage by how many miles he puts on it before he fills it up(wrong way), or is he taking the miles driven, and deviding the amount of fuel used into that to determine mileage(proper way)
if he is just going on how many miles he is driving, you can't judge gas milage that way.

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Psssst.... 89 would have been a Windsor engine.
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Thanks Jim, you are right, I should have said "W" (just an upside down "M" after all). Still same bore and stroke. Was the last year for the 351M - 1985?
Ed
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I was wondering if you were standing across your desk and typing upside down..... it's a good story - stick to it 8^)
Going from memory (at our age that's always risky) I have to opine 81ish/ 82ish.... 85 was port fuel injection for the pick-up 302 and a 4bbl 351 could be had that year.... 84 was definitely W....
Look at us... we are discussing things that are nearly qualified to be called antique (much like I feel these days....).

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Right - sorry. Still 4" bore x 3.5" stroke. Should have said 351 "W".
Ed
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My friend's 1989 Ford Bronco ... V-8 350 engine ... 250,000 miles ... 28 gallon tank and 380-430 miles to a tank depending on the weather ... live 3000 feet above sea level.
April 2006--fuel system cleaning -- tech code 15; and also 8 cylinder tune-up. Car ran well with usual gas mileage.
August 2006--car stopped running -- tech code 15 -- replaced 8 fuel injectors (MP 10898 Reman Fuel Injectors, 1 plenum gasket, 8 spark plugs, and 1 fuel press regulator). The car still runs well but gas mileage has dropped to 320 miles per tank. Any ideas why? __________________________________________________________
Gas mileage went from 405/28 = 14.5 mpg to 320/28 = 11.4 mpg? The obvious suspect is the rebuilt fuel injection system, but if it ran that rich, it would not run as smoothly as your friend says.
Another possibility is that there was no mileage change, instead, the fuel gauge has become defective and reads empty too soon, so a tank "fillup" puts in less fuel. It is difficult to guess at the problem without a more accurate mileage figure. Try this:
1. Fill the tank. Record the odometer reading. 2. At next 2 tank refills, record the gallons taken on. 3. After the second refill, record the odometer reading. 4. Calculate the gas mileage: mpg=(total gallons in 2 refills)/miles driven.
Another possibility is that your friend who estimates his mileage in "tanks" of fuel, never really knew his gas usage and that he's giving you misinformation.
Good luck.
Rodan.
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And there's another factor besides the grossly inaccurate "miles per tank from memory" with no solid numbers to back it up...
Somewhere in the late 1990's the entire US went to oxygenated low- emissions fuel with either MTBE or Ethanol blended in "for cleaner air", and that gets about 5% less MPG because of a lower overall BTUH Per Gallon content.
California got stuck with it first in the early 90's, then the Feds thought they might as well make the rest of the urban areas in the country "with bad air" suffer with it too.
--<< Bruce >>--
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Actually the "entire" US has not gone to oxygenated fuels. In fact there are lots of different fuel requirements across the US. In my area (east central NC) for a few years we got stuck with oxygenated fuel in the winter months (either MBTE or ethanol as the additive), but now we only have to suffer with 7.8 RVP Gasoline (RVP = Reid vapor pressure see http://www.epa.gov/otaq/regs/fuels/420b07007.pdf ).
Mobil has a good Gasoline FAQ at <http://www.mobil.com/USA-English/GFM/Products_Services/Fuels/Gasoline_FAQ.asp and this includes a link to a US Fuel Requirements map (http://www.mobil.com/USA-English/GFM/Files/US_Gasoline_Map.pdf ). Here is what Mobil has to say about gasoline:
What is Reformulated Gasoline? Reformulated gasoline (RFG) is a special blend designed to reduce harmful automotive emissions. RFG must be marketed in those areas of the United States where air quality doesn't meet the ozone requirements of the Clean Air Act Amendments. It is formulated to release fewer volatile organic compounds (VOCs), has a lower benzene content, and must contain oxygenates like Ethanol or MTBE.
For more information on RFG, visit the API's web site http://www.api.org /.
What is California Cleaner Burning Gasoline? California CBG is a type of reformulated gasoline designed to reduce emissions. It reduces the emissions of NOx and volatile organic compounds, has lower benzene and sulfur levels, and limits the amounts of aromatic and olefinic compounds in the blends. It is required throughout the state of California.
For more information on California CBG, visit the California Air Resources Board web site http://www.arb.ca.gov ./
Do your gasolines contain MTBE? MTBE and Ethanol, as well as several other alcohols and ethers, are all classified as oxygenates. In many areas of the country, oxygenates are required to be part of the gasoline formula. In those areas, our gasolines will contain either Ethanol or MTBE or similar ethers. These areas include those requiring RFG, California CBG and others [US Fuel Requirements Map http://www.mobil.com/USA-English/GFM/Files/US_Gasoline_Map.pdf ]. In addition, ethers like MTBE are used as a common blending component of conventional gasolines, although normally at much lower levels than in RFG. Therefore, our gasolines may contain MTBE or other similar ethers. In all cases, however, their use will be at or below levels approved by the EPA.
Do your gasolines contain Ethanol? MTBE and Ethanol, as well as several other alcohols and ethers, are all classified as oxygenates. In many areas of the country, oxygenates are required to be part of the gasoline formula. In those areas, our gasolines will contain either Ethanol or MTBE or similar ethers. These areas include those requiring RFG, California CBG and others [US Fuel Requirements Map http://www.mobil.com/USA-English/GFM/Files/US_Gasoline_Map.pdf ]. Since most states require labeling of dispensers when Ethanol blended gasolines are provided, you can easily determine if Ethanol is being used during your next fill-up.
End Quote
Chevron also has an excellent web site discussion gasoline. See http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas /. And of course you can always read what the EPA has to say at http://www.epa.gov/otaq/gasoline.htm . One link from thje EPA page address the question of fuel economy and performance changes due to oxygeantes. See http://www.epa.gov/otaq/regs/fuels/ostp-3.pdf .
Ed
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it could be sooooo many things. I'll add to the long list to come, his tires have lost air over this time.
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