OBD II Data

steambao · 17-05-2012, 01:46 AM

Hi all,

I recently bought myself a OBD II scanner (cheapo one off ebay, and Torque on Android) and am having quite a bit of fun seeing what goes on in my ECU (my main reason to figure out my bad mileage once and for all - and so I know what to service). Has anyone tried using OBD II scanning software on the Focus?

If so, what are your fuel trim's like. I'm assuming we only have short term and long term in bank 1?

My long term fuel trim likes to hover at -5%, and is constantly going opposite to my short term fuel trim (which goes from -5% to 10% all the way up to 15% on throttle).

I'm assuming my engine is running rich, and explains why my mileage is so poor.

What are your trims like? Does your long term constantly change, is this normal?

A Log of fuel trims, Manifold Pressure both graphed here: (can't upload excel file bigger than 72kb, so in my dropbox)
http://dl.dropbox.com/u/28441455/logged_trim.xls

Russ · 17-05-2012, 08:16 AM

I doubt many people on here would have used a diagnostic tool such as this on their Focus or other car unless they had the need to and or knew what they were looking for

Maybe if someone with the same model Focus as yours would allow you to plug in to their port and take readings to compare values it may give you something to work off in finding where your excessive fuel consumption issue lies

Nolz · 17-05-2012, 07:37 PM

I was hoping to be able to post something up. However today I discovered that the bluefin I was sold isn't for the LW as it doesn't exist yet :( so I guess I can't play in this thread haha

ratter · 17-05-2012, 07:55 PM

those trim numbers, well the negative numbers indicates the ecu is pulling fuel based on the information the o2 is sending, that is to mean the car is not running rich, if the trims are working, and they appear to be, the commanded afr should be occuring in the engine because the trims have corrected it.

steambao · 19-05-2012, 04:49 AM

Quote:

Originally Posted by ratter

those trim numbers, well the negative numbers indicates the ecu is pulling fuel based on the information the o2 is sending, that is to mean the car is not running rich, if the trims are working, and they appear to be, the commanded afr should be occuring in the engine because the trims have corrected it.

I think this is exactly right! I think the trims are doing their job, and glad the engine isn't running rich. I'm assuming my assumption that long term fuel trim should be constantly near 0 +/-1%, for a healthy car, is wrong?

Reading on google some people say long term fuel trim is the 'smoothed out' version of short term fuel trim and others it's the ECU's way of remembering what it needs to auto add/subtract continuously to get a proper AFR - all very confusing and all.

Also, which part is the o2 sensor for the focus specifically? Is it the part labeled 'cylinder-head temperature sensor' (in image below), the thermostat, or the MAP? Not sure how the Focus calculates oxygen amount. Confused about these three parts.

Russ · 19-05-2012, 07:57 AM

I would think the cylinder head temperature sensor would be for monitoring the coolant temperature, I'm pretty sure you'll find the O2 sensors are located on the manifold and exhaust engine pipe. I'm not a mechanic but I've changed a couple of O2 sensors over the years and they have always been on the exhaust system or manifold

ratter · 19-05-2012, 09:12 AM

o2 sensors are in the exhaust and trims are never at 0 and they do vary all the time