Fuel Trim Chart

I ran into a very informative chart at Eastern Catalytic Tech Tips.

Read more here on their write up here - http://www.easterncatalytic.com/education/tech-tips/fuel-trim-can-be-a-valuable-diagnostic-tool/


I like this diagram they have.

Image credit goes to the Eastern Catalytic.

X-trail: 02 Sensor

I was comparing the O2 sensor signals between the X and a i10. The i10 looks like it has a more healthy 02 signal.

When i floor the pedal, the O2 signal responds shows exactly as described in scannerdanner's tutorial. As for the X, there was plenty noise & deviation from the expected signal form.

Do i have a lazy O2?

Gonna need more tutorials........

X-trail: Fuel Trim

Kind of dragged my feet updating this.

Plugged in the OBD2 donggle. Ran the software.

What did i find?

Short Term Fuel Trim -> +10 range

Long Term Fuel Trim -> +10 range

That would make total fuel trim -> +20% range 

This would mean I have a lean condition

When I throttle the car to >3000RPM total fuel trim drops under 5%. Per scannerdanner's tutorial information, he would say I have a vacuum leak.

So i need to detect where that vacuum leak is by doing one of the below

- spray bottle

- carb cleaner

- propane

- smoke

Which should I choose?

Notes: Fuel Trim

High Total Fuel Trim at Idle

Low Total Fuel Trim at higher RPM

-> Possible vacuum leak

Low Total Fuel Trim at idle

High Total Fuel Trim at higher RPM

-> Possible dirty MAF sensor

Paul Danner - Dirty MAF Case Study Video below.

Case Study: Lean Condition Variables

This is one very interesting case study shown to us by Paul Danner. Interesting how one missing air filter can force the ECU to make the engine run lean (also poor on FC since the fuel trims are all the way to the roof)

Short Term Fuel Trim
Long Term Fuel Trim