need help squeezing out some mileage
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Joined: Jul 2009
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need help squeezing out some mileage
my 91 f-150 4.9 auto is getting a crappy 12mpg. I need any and all info on how to squeeze some more mpg out of my truck. I just recently had to put cats back on it to pass inspection (grr....hadn't had them on for the past 10 years and always passed with flying colors...not anymore) and I know that's affecting it. I know some of you guys are getting 16-18 mpg outta these trucks...how the hell are you doing it? everything is stock on my truck drivetrain wise and wheels/tires.
All help will be greatly appreciated guys. I know it's possible.
All help will be greatly appreciated guys. I know it's possible.
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
How many miles? If its close to 200K you may need a rebuild on it. A full ignition tuneup as well as a air filter will help. A KN filter got me a xtra MPG on the highway. Try a tranny filter and flush. Other then that dont ram the throttle and thats about it.
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It's got almost 200k on the odo, but it was rebuilt around the 120k mark. It could use a tuneup-it hasn't been quite a year since I did one-and I've had a k&n filter in it before, but didn't really see any improvement. If I knew where I could get it inspected without it having to have cats, I'd take them back off, I know that'll help some. I've heard about guys advancing the timing and getting a little more power and mileage out of these motors, and I can tell (smell) that it's been running rich for quite some time now, but I don't know how much to advance it. The E4OD isn't helping, I know. I've thought about changing out the 3.08s in it and replacing them with 2.73s to try to combat highway cruising at speed (70). The only "mods" to the motor are duals (with dual cats 
) and it's been bored 0.040 over when it was rebuilt. The tranny filter is clean, just had that replaced not too long ago. Would a gear oil change help any? I can't remember ever changing the rear end oil ever. And I try not to ram on the gas....but sometimes I just can't help it 
.
) and it's been bored 0.040 over when it was rebuilt. The tranny filter is clean, just had that replaced not too long ago. Would a gear oil change help any? I can't remember ever changing the rear end oil ever. And I try not to ram on the gas....but sometimes I just can't help it .
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Swaping out the gear oil every 2 to 5 years is just good prudence. Your O2 sensor may be heading south due to age causing the rich smell. My main guess is the sensor. A 3.08 gear should nail you around 19 mpg. Also, try driving on the highway in direct drive (3rd). You may be lugging the engine too much.
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