Gas Mileage decrease please help
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Junior User
Joined: Aug 2005
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Gas Mileage decrease please help
I have a 302 in my F-150. I installed a comp cam and a set of freshened up 5.0L mustang heads. The cam is a 114 lobe seperation .481 intake and exhaust lift i believe like a 258 duration cam. My truck now likes to idle at 1300 rpm. It was surging prior to me cleaning the throttle body but it was idling down to 675 rpm. now it doesnt idle down but no surge. on a scan i had performed the injectors were pulsing alot the O2 sensor was giving me an error so i replaced it. Anyways half a tank later i have only got 100km's on the half tank. thats about 60 miles. I used to get 175km's on the top half maybe even 200km's. fuel economy is down close to half. any idea's?
Senior User
Joined: Mar 2004
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did u run that half of a tank with the o2 sensor messed up? 02 sensors are crucial to gas mileage.. Check for any codes again..
Would a cam cause his idle to rise?
Also... a little side thing... Hows it feel with the cam in it power wise? I have a 5.0 as well and was thinkin about gettin one.
Would a cam cause his idle to rise?
Also... a little side thing... Hows it feel with the cam in it power wise? I have a 5.0 as well and was thinkin about gettin one.
Post Fiend
Joined: Oct 2003
Posts: 6,214
Likes: 13
From: New Jersey
Bigger heads, more aggressive cam, high idle all equates to more gas.
IAC and vacuum lines are good things to check, Quicklook2 was right on the money there.
O2 sensor is also key, as Turboguy suggested.
Your idle should be 800-900. Heck, my 351W-powered crewcab idles at 780.
IAC and vacuum lines are good things to check, Quicklook2 was right on the money there.
O2 sensor is also key, as Turboguy suggested.
Your idle should be 800-900. Heck, my 351W-powered crewcab idles at 780.
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Junior User
Joined: Aug 2005
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The Truck is a 92 F-150. Yes it is a computer controlled truck. Comp Cams claim this is a computer controlled efi friendly cam. The O2 sensor was replaced about a 1/4 tank ago. My wife says the check engine light came on for her the other day. ill have to check the codes again. The 334 code came up before and i imagine thats the code still has to do with voltage to high to the egr. When i disconnect the idle control sensor (which i cleaned) i still notice the idle going up and down sometimes. I waas under the impression that that meant that the tps is going. i checked the voltage on the tps and it is set up now, however i did notice that the sensor isnt smooth to rotate when i uninstalled it. perhaps i should look at changing that. I used a tiger torch of propane and ran it all over the intake and vacuum lines to see if the idle would jump any and it didnt so i am now assuming there are no vacuum leaks.
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Senior User
Joined: Jul 2001
Posts: 250
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From: South Carolina
I would definatly lean twords the tps. Also a custom chip for your new parts will get the full use of them. Let us know what you find. Hippie
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Thread Starter
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Junior User
Joined: Aug 2005
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well i cleaned the iac and now the truck idles down to where it is supposed to be. the other thing i did is I reset the computer. I have thought about a performance chip but i was under the impression that i would have to run premium gas is that the case?
Post Fiend
Joined: May 2004
Posts: 11,289
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From: Lakewood, Ohio
why don't you drive it for a week or two and give yourself some time to get it running right as it is. it should be plenty peppy enough and throwing in a new chip would just add another variable.
Freshman User
Joined: Feb 2005
Posts: 47
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From: Minnesota
Just remember... A little chip can mean a big drop in fuel economy. Learned that with my buddy's 302 150. He now gets 7 city and 11.5 hwy. These are below averages after a chip, but that doesn't make the numbers hurt any less.