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Category: Ford
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Experience:  ASE CERTIFIED TECHNICIAN ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
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2002 Ford Focus: 130k gas mileage has deteriorated to 20mpg

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I have a 2002 Ford Focus ZTS. It has about 130k miles. In the last few months, my gas mileage has deteriorated to 20mpg. We have cleaned and regapped the spark plugs, changed the plug wires, and replaced the EGR valve (due to OBD code). The EGR still has insufficient flow, and next step is to get the sensor & vacuum solenoid. However, we're not sure if that will clear up the transition problem.

When I'm not accelerating hard, the car stutters - A LOT when the air conditioner is on. It happens in all gears. In traffic I feel like I'm riding a bucking bronco. Also, I've noticed the "shift gears" light no longer comes on, but I'm not sure at what point that happened.

Any suggestions?
Hello there

Here is a list if things to check that can cause bad gas mileage.

Potential Causes:

Malfunctioning Fuel system. Fuel pressure too high or too low.
Leaky injector or fuel pressure regulator.
Bad or lazy Oxygen Sensor or sensors
Sensor Inputs.. Bad or Skewed Coolant temp sensor, mass air flow sensor, Map sensor, Throttle position sensor

Bad engine grounds

Transmission — Transmission shifting
Anything in the drive train. Bad calipers (hanging up), binding drive shaft or bad wheel bearings or even low tire pressure

Engine mechanical.. Valve timing off by timing chain or belt, restricted exhaust, low compression and or valve train problems... valve mot sealing properly, bent valves carboned up valves or motor
Engine Maintenance - Change your oil, spark plugs, and air filter regularly. And go to a repair shop if your "Check Engine" light comes on-a faulty oxygen sensor could be the cause, lowering your mileage significantly.
Engine Oil - Use the grade of motor oil recommended by your vehicle's manufacturer. Motor oil that bears the American Petroleum Institutes "Energy Conserving" performance label contains friction-reducing additives that save gas by letting your engine work more easily.

Fuel/Intake System Restrictions - Dirty air filters, fuel filters, and fuel injectors make your engine work harder to generate the same amount of power at the wheels, thus wasting more of its own energy and reducing mileage. This is probably the most common cause of gradual fuel economy loss because, unless the problem is severe, computer controls can usually compensate such that the average driver doesn't notice any issues. This is why it's important to stick to maintenance schedules, even if it seems unnecessary at the time.

Low tire pressure allows a greater portion of the tire tread to contact the road, increasing friction and sapping power (it also causes accelerated and abnormal tire wear). Wheel alignment problems cause similar issues by forcing tires to "drag" across the pavement to some degree, rather than roll smoothly. Less commonly, malfunctioning braking or all-wheel drive systems can cause additional drag at one or more wheels, wasting power.
Customer: replied 5 years ago.

What about the stuttering? That's a huge list of things to try/consider. Is this a common problem? What would you check first? OBD hasn't indicated an oxygen sensor problem.


I have read some forums and read there were power issues related to head gaskets & coolant leaks when heater works only when accelerating (they said it was rare, but my heater only heats when accelerating). Would I see any other issues related to that?

When was the last time the engine was tuned up? No, not just plugs, but a full tune up! The whole nine yards! Any part of the secondary ignition will do this including the ignition coil or coils! This sounds like a classic ignition misfire! They usually go bad under a load like under acceleration, but can be noticeable at any time. It is very important to have your engine equipped with good tune up parts or you may be causing damage to other components of you car like the catalytic converter which can be expensive!

Possible causes:

Ignition misfire causes by any bad tune up part and or ignition coil or coils.
Bad spark plugs, spark plug wires and cap and rotor (if equipped)
Wrong tune up parts spark plug, wires etc...

Insulator cracks.
Improper gap.
Burned electrodes.
Heavy deposits.

The quickest way to check the ignition components, is by looking closely for leaking secondary voltage. Visual look at all the tune up parts to see if you can see any sparks coming from any of the wires or coil (or coils) when the vehicle is running. If not, you can put your hand on the coil/coils and wires when the engine is running and see if you feel any small voltage leaking form the tune up parts. Check spark plug wires by connecting ohmmeter to ends of each wire in question. If meter reads over 30,000 ohms, replace wire(s).
ALso, with engine running, spray coils and plug wires with fine water mist to check for shorts.

It will leak secondary ignition voltage from the tune up parts caused by high resistance from carbon tracking if they are bad. This is very common if the tune up parts are not changed regularly!

If any is found, the tune up parts are simply bad an will need to be replaced! If none is found than you can spray a mist of water on the tune up parts when the engine is running and see if that causes the engine to stumble or run rough at all. Again, if it does, the tune up parts are bad and will need to be replaced!
AMEDEE and 6 other Ford Specialists are ready to help you
Customer: replied 5 years ago.

Okay - the fact that it's worse when it's raining & the engine gets wet makes it sound like the secondary ignition voltage leak is it. I'll try the things you suggested. Thanks for your help.

You bet!

THanks for the accept!

Have a great day!