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1991 F-150 4WD 351, VERY poor mileage

Tiny
ROCKWELL
  • MEMBER
  • 1991 CHEVROLET TRUCK
I just bought a 1991 4WD F150 with 117,000 miles on a 351 engine, drove it home on the highway, and averaged 10 mpg at 65 to 70 mph. Now that I am driving it in town, I average 5 mpg. The engine starts and runs terrific, and has mad power. Pulled the plugs, and it looks like the engine is burning LEAN. The transmission shifts well, overdrive works, and transfer case shifts smoothly between 4wd, 2wd, high and low ranges. I put in a new air filter, and changed oil and filter, using Mobil 1 synthetic. Is this typical 351 mileage (which is worse than big block Chevys I've owned) or do you have any idea what might be wrong? I'm perplexed.
Thanks,
Rockwell
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Wednesday, March 15th, 2006 AT 7:56 PM

2 Replies

Tiny
RAYHUT
  • MECHANIC
  • 134 POSTS
Thats common with a 351 I have one in a 67 500 and I get poor gas milage. And my 302 has better gas milage not much but better.
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Thursday, March 16th, 2006 AT 5:56 AM
Tiny
ROCKWELL
  • MEMBER
  • 2 POSTS
Thanks for the reply. It's somewhat comforting to know that I'm not alone, but a 351 is not that large of an engine. There should be a way to improve the mileage somewhat.
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Thursday, March 16th, 2006 AT 10:03 PM

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