Power and MPG problems..
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Junior User
Joined: Oct 2005
Posts: 75
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Power and MPG problems..
i have a 99 f150 4x4 4.6l with 130,000. I have been getting around 17 mpg on city/hwy trips.. on trips with the majority being city, i would get around 15.5 mpg.. now i am getting a little over 12 mpg. I can feel a miss at idle. when it is in gear is when you can feel the miss the worst, in park or neutral it is not as bad. At times when accelerating it does fine and at other times i have to give it more gas to get the same if not a less response...kinda like it is being held back by something. the plug and wires are a around a 1-2 years old.. Does the problem lie in the coil packs? or a vaccum leak somewhere? or is it the plugs and wires? I can also hear a slight chattering sound at times while accelerating. Any help will be greatly appreciated...
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,079
From: St Louis
Low grade misfire.
Probably plugs or wires, possibly the coil.
A lot depends on what plugs and wires were used at the last "tune-up".
If you can induce the conditions that are causing the symptoms, you can make the fault apparent enough to the computer to set a fault code. Otherwise, you'll need to dig into the Mode 6 data and look at the misfire counts to identify the misfiring cylinder(s).
Steve
Probably plugs or wires, possibly the coil.
A lot depends on what plugs and wires were used at the last "tune-up".
If you can induce the conditions that are causing the symptoms, you can make the fault apparent enough to the computer to set a fault code. Otherwise, you'll need to dig into the Mode 6 data and look at the misfire counts to identify the misfiring cylinder(s).
Steve
Tuned
Joined: Dec 1999
Posts: 464
Likes: 1
From: Bismarck USA
I would say a tune up is in order. If the plugs haven't been changed, do them. For best luck, just get the Motorcrafts. Might as well do the wires. New fuel filter too.
But I'd also see about the emissions passage-way in the intake. Those can get carbon'd up too.
Did the mileage suddenly drop, or was it gradual over say 10k miles?
But I'd also see about the emissions passage-way in the intake. Those can get carbon'd up too.
Did the mileage suddenly drop, or was it gradual over say 10k miles?
Senior User
Joined: Oct 2006
Posts: 111
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i have the same problem. and i changed the plugs, wires, oil, oil filter, fuel filter, and put in a k&n air filter. and still. nothing works and that noise is still there. i think we may have the same problem because that;s exactly whats happening to my truck. i had the noise before. and within the last 2 fill ups my mpg have dropped from around 18 to 10-12 and i only use premium or mid grade gas
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Junior User
Joined: Feb 2005
Posts: 75
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O2 Sensor maybe? I had a bad one on the passengers side in front of the cat and was getting horrible MPG.
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Freshman User
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check your #4 plug i had that problem and replaced just about every fuel and ignition component i could. come to find out a heater hose had a small drip over the #4 plug and was getting moisture in there. only other thing i can tell you is fill up your plug wires with dielectrical grease. there are other possibilities obviously just stating an experience i had
New User
Joined: Feb 2007
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I think your rattle might be coming from a cat. If it's getting piled up inside, that would cause a decrease in power and MPG as well. I have had the same problem, but it would come and go. It wasn't consistant. I'm planning on changing my whole exhaust system starting with headers, and getting 2 high flow cats (instead of the 4 oem cats) and a good cat back exhaust system. Let us know if you figure out what the problem was!