Fuel Trims and Live obd data

[Fadi]

I have Ford fusion energi 2013 , and iam facing a bad fuel economy and a bad acceleration , I have conected my bluedriver to the obd port , and this what I have found , I hope some one can help me with these values

Long term fuel trim is 7.8%
Short term fuel trim is between -3% to 3%
Mass air flow rate at full throttle is around 50 g/s to 55 g/s
Intake manifold abselute prusser when acceleration is between 22 hg to 27 hg
Catalytic converter tempreture between 500 C to 850 C at acceleration
O2 sensor voltage between 0 to 0.800 at Max

Does these readings are normal ?

 

[55Test]

That long term fuel trim number concerns me. If I'm not mistaken, that number shows the PCM is commanding the fuel injection system to push an additional 7.8 percent fuel over the normal rate to achieve a standard fuel/air mix. I'm not familiar with your particular car but I'd have a mechanic check for an exhaust leak or vacuum leak

 

[Fadi]

Thank you , then the LTFT should be 0 % ?

 

[55Test]

Generally, yes. In a well running engine the long term fuel trim should be right around the 0 number

 

[Lubener]

Originally Posted By: Fadi
Thank you , then the LTFT should be 0 % ?


In a perfect world. Genarally +/- 5 percent is acceptable.See what the trim is at idle. A vacuum leak will be most noticible at idle and the trim will shoot up and lessen at higher engine speeds. I might check fuel delivery which would show up during peak engine demands.

 

[Fadi]

But what I have noticed than the LTFT come down until around 4 %, when ever I push the car to 2000/2500 RPM , does this mean anything?

 

[Fadi]

When ever I remove my foot from the pedal it come back to 7.8 again

 

[Tman220]

If that HP figure for your engine I looked up is correct, (141 HP) then your mass airflow sensor (MAF) should be showing about double the 50-55 g/sec reading you are getting right now. 141 HP should take about 100-110 G/sec airflow to achieve.

Although, if your MAF was only reading roughly half of what it should then I would expect your fuel trims to be a lot more messed up.

I would start by cleaning the wires on your MAF sensor and seeing if it changes anything.

Also, if you are on 100% engine power, (no battery help) a full size car such as that will use roughly 15-25 G/sec air to maintain 60 MPH (97 km/h)on level ground. If that reading also seems off you might need to clean or replace your MAF sensor.

 

[Ethan1]

That LTFT is not that bad. You didn't mention if there is an SES light, wrench light, or any pending codes...

 

[eljefino]

Wander around touching your wheels and see if one is hotter than the rest. You could have a sticking brake.

 

[Trav]

Check for a small crack in the accordion hose or loose clamp from the MAF to the throttle body.

 

[punisher]

A LTFT of around 7-8% isn't something by itself to worry about. Codes don't get set until it hangs around 25% for awhile. In this case you have drivability concerns as well.

Causes range from a vac leak/unmetered air leak (lean trims at idle that go towards 0 under load) to a possible O2 sensor concern. Small vac/air leaks that aren't big enough to set a code usually cause a rough idle at the worst. Usually no great effect on mileage. A bad O2 sensor is usually something to look at if you are SURE there is a drop in mileage.

When deciding between MAF, fuel pressure, and 02 concerns- MAF problems usually trim rich at idle, lean under load. Vac leaks trim leanest at idle and trend towards 0 trim under load. Low fuel pressure- Normal to lean at idle trending leaner under load. High fuel pressure- Rich idle trims trending leaner under load. Bad O2 sensors can be tough to diag. Many times they "dropout" for a few seconds and you can catch it with a data logger. There have been occasions where I have thrown an O2 sensor at a vehicle because I couldn't find any other reason for a lean code.

 

[SHOZ]

I find it better to watch the absolute load values (Volumetric Efficiency) and O2 voltages(higher is richer).

 

[Ethan1]

Originally Posted By: eljefino
Wander around touching your wheels and see if one is hotter than the rest. You could have a sticking brake.


It could be the battery, too. These are all just WAGs. You can't do a driveability diagnosis over the internet on any modern car, let alone a plug-in hybrid