"Fuel Trim" CEL

[toomey200]

my CEL was on im my 95 talon awd and i ran the code and it said fuel trim so i replaced the upper O2 sensor, reset the codes and then ~10 miles down the road the light came back on for the same thing. anyone have this problem before? thanks for the help

 

[zippyshoe]

There are many problems that can produce a fuel trim malfunction. Here are some of the most common causes:

1. Faulty front O2 sensor. (which you have already ruled-out)
2. Faulty fuel injector.
3. Boost/vacuum leak.
4. Leak in your exhaust system before the front O2 sensor (cracked exhaust manifold, turbo's exhaust-side housing, O2 sensor housing, one of the gaskets in this area).
5. Faulty mass airflow sensor.

If you have a logger available, you may want to monitor your front O2 sensor voltage and long-term fuel trim - this will tell you whether the ECU "thinks" your car is running too rich or too lean.

 

[toomey200]

i removed the honey combs from the MAF sensor could that be the reason?

 

[92awddsm]

i removed the honey combs from the MAF sensor could that be the reason?

Yes, that will cause the problem. You should not remove the hc from the mas unless you have an afc or some other tuning device to compensate for the additional airflow. With a 2g mas, you should not remove the hc at all. It is not a restriction untill you are making 450+ hp and you are a long ways from that. Reinstall the hc before you hurt the engine from running lean.

 

[djseclipse]

There are many problems that can produce a fuel trim malfunction. Here are some of the most common causes:

1. Faulty front O2 sensor. (which you have already ruled-out)
2. Faulty fuel injector.
3. Boost/vacuum leak.
4. Leak in your exhaust system before the front O2 sensor (cracked exhaust manifold, turbo's exhaust-side housing, O2 sensor housing, one of the gaskets in this area).
5. Faulty mass airflow sensor.

If you have a logger available, you may want to monitor your front O2 sensor voltage and long-term fuel trim - this will tell you whether the ECU "thinks" your car is running too rich or too lean.

Agree, I had the same code. Replaced the upstream o2 sensor, fixed it for a while then it came on again. Turned out that I had a huge boost leak.