Ok I am in some real need of help, My xt6 just started running really poor and really really rich, this was about a week ago and i had it to my local dealer, they put a new cap and rotor, and some dry rotted vacum hoses on it. I got it back running about the same maybe a little bit better. I took it home and changed the plugs, the front 4 where fowl horribly. and the back two looked really good. i put another set in and got the same result. I would really hate to have to get rid of it. It was my first car. And its making a mess of my sti with the snow and all.

Check your MAF, it may be dead or dying causing a rich mixture. Beyond that the O2 sensor has a hand in mixture control, check the output of that as well.

thanks for the help the, where is the o2 sensor, i replaced the oxygen sensor too. Do you guys have any idea wwhy it would only be fowling 4 out of 6 plugs

02 sensor = oxygen sensor..

 

i'd sheck the maf as well and clean it real well..

If it just "all of a sudden" happened like this, I would say what they are saying. Make sure you got the right O2 sensor, and that you hooked it up right. Try cleaning the maf sensor with electric parts cleaner and stuff.

 

If anyone knows a better chemical to use on a MAF that 1. won't hurt it, and 2. cleans like a mother... post it.

Two items to check

1) not mentioned yet is faulty or corroded connections on the fuel injection coolant sensor.

The resistance of this sensor vs temp is inversely proportional

As the temp of the coolant increases the resistance decreases.

Now we have corroded connections which add resistance - added resistance means a cold engine - ECU dumps a rich mix and may never go into closed loop. Clean the connections.

2) 02 sensor ground. The ground for older 02 sensors is the exhaust system. Rust and rubber connections can make this see a high resistance, the signal is so small ( < 1V dc) that any resistance will cause problems.

I ground mine by connecting a ground wire on the 02 sensor body with a heater hose clamp.

The 02 sensor is in the top of the exhaust "Y" pipe.

 

The test for either of these problems is relatively easy.

In the boot (trunk) under the passenger side parcel shelf is the ECU. It has an LED on it's face that is called the "02 monitor"

Warm the car up, look at this monitor - if all is "ducky" it will be flashing in a non rhythmic fashion with a freq of about once every 3 to 5 seconds.

If not - try the above fixes.

Hope this helps

Hey Subaru7291,

 

It would be very helpful to know the mileage on your car. From your description, it sounds like a bad coolant temperature sensor.

This sensor tells the computer how much gas to put out as soon as you turn the car on. Was your "local dealer" a Subaru dealer?

 

The best way to pinpoint this problem is to pull codes from your car's computer.

 

If the MAF is bad, usually the car will run for 5 seconds and shutoff. However, it is a good idea to clean the connections.

 

The o2 sensor has a direct relation to the gas mixture so that is a likely possibility. So to discern between the coolant temperature sensor and the o2 sensor, you must note the idle when you turn the car on while it is cold first thing in the morning. Does your RPM needle jump up and down until the car warms up? Is it necessary to idle the car with your foot on the pedal until it warms up? If so, these are indications of a bad coolant temperature sensor; sometimes you don't get codes for this.

Does your "check engine" light come on and stay on?

 

As well, you have a throttle position sensor which could be bad or out of adjustment.

 

The coolant temperature sensor is to the left and just behind the alternator. The wires for this sensor can be frayed or corroded. Using a small screwdriver, remove the clip from this sensor; unplug the wires and look for green corrosion. Clean it out or replace the sensor. Note: If you XT has more than 130,000 miles on the coolant temperature sensor is past it's prime. What can happen is that your plugs are fouling while you warm up and then you run poorly from that point.

 

This is guesswork without seeing your car. A Subaru dealer has the diagnostic tools to tells you which sensors are bad if any or whether your front four injectors are bad.

 

One further issue: the o2 sensor and the oxygen sensor are one and the same.

 

Good luck.

 

Mark in Connecticut.

THANKS GUYS FOR THE TIPS, THE CAR HAS 114,000 MILES ON IT, THE SENSOR IT SELF IS ALL GREEN FROM CORRISION, I TOOK THE MAF OFF AND IT WAS A LITTLE DIRTY BUT I JUST FIGUERED THAT WOULD BE FROM 114,000 MILES. THE DEALER IS A SUBARU DEALER I JUST DON'T THINK THEY WANT TO SEE ME CAR.

While you are at it, may as well change your spark plug wires as well. I see you mentioned your caps and plugs were changed but I don't think I have seen your spark plug wires where changed as well.

 

Also, check your PM (Private message) as well. Sending you info/link.