Bad MPG
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Junior User
Joined: Jan 2002
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Bad MPG
I just had my truck motor and tranny rebuilt it a 90 with a 300 4x4 manual 5speed. It was getting 14 to 15 intown before it was rebuilt. But after i got it back it has ran like ##### and get 9 to 10 miles intown and 13 on the highway.My injectors were replaced pistons ring rod, cam, valves,the head was cracked and it was welded back and fixed.new coil k&n airfilter poweraide throttle body spacer.New split fire plugs. Everything the little silver cyclander obove the throttle body. new o2 sensor exhaust (duals). I think its running a little rich but don't now where to start pleas help.:-X23
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Joined: Jul 1999
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Bad MPG
Ok , What was the problem with the engine & trans that they needed rebuilding ? If you got that mileage in town before the rebuild there couldnt have been too much wrong with it . First thing I would do is get rid of the Spiltfire plugs . What is the purpose of the throttle body spacer ? What brand of O2 Sensor did you use ? The aftermarket ones arent always calibrated for the engine its used on . Get a reading on the fuel psi & see what it says & make sure there are no intake or vacuum leaks .
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Junior User
Joined: Jan 2002
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Bad MPG
The throttle body spacer was to get a better torgue curve and better gas milage.The splitfire plugs are good arn't they because motorcrafts are cheap so i thought they wouldn't be as good as a splitfire. What plug would you use if you had lots of money to spend on horsepower. The o2 sensor was a borg and worner. My engine was using alittle oil and the tranny was gettin hard to ##### into 2nd.So if i fixed them i would get better gas milage and the cam was same as stock. My engine revs up when you push in on the clutch like it thinks its still cold and when you let off the gas. It doent slow down it will still run for a fer second like im still pressing on the gas or something. I kind of figured it was running a little to rich.
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Joined: Jul 1999
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Bad MPG
As far as im concerned the Motorcraft plugs , cheap or not , are the best for that engine , Just because something cost more doesnt mean its better . The throttle sticking problem , high revving when you release the gas pedal is likely either the air bypass valve , but you said its new , so Id guess either the throttle plates need cleaning or the throttle body spacer is playing some role in keeping the throttle open some when you release the pedal . Check to make sure the cable linkage isnt binding .
Junior User
Joined: Oct 2001
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Bad MPG
just a thought about the sticking throttle. I made a carb spacer for my mustang, and it was just lightly miss aligned so that the throttle blade would barely rub against the opening in the spacer, this was causing my throttle to stick open partially for a moment before it would close. Perhaps your throttle body spacer is a tad missaligned...or the hole slightly too small?
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Joined: Jul 2001
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From: torrington,ct
Bad MPG
i had the same problem with my 88 but it was only on real cold mornings. and no it wasnt because the engine was just cold kinda thing. we think we narrowed it down to there being alittle oil in the linkage from when i had an oil leak, and the cold oil was making the linkage sticky. once i ran the truck for a few miles and got the whole truck nice and warm it would stop. i ment to spray some wd 40 on it but i never got around to it and it stoped.
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