Ford Fiesta 2011 1.4L – Fuel Trims

[Dmitry Tolstoy]

Greetings!
Recently I’ve observed strange fuel trim data, idk how to explain those huge differences.
Car is running at Idle, closed loop, warm.

STFT = 16.4% (Too lean on short?)
LTFT = -20% (Too rich on long ?)
:huh:
O2 bank 1 voltage seems running up and down properly, 0.790 V max and around 0.220 V min.

Overall the car seems to perform fine, steady rpm, no CEL, no codes stored.

Thanks in advance!

Topic

[Richard Kirshy]

Have you tried to observe the trims while holding the rpm up around 2,000 and see if the trims change radically?
You may be looking at a possible vacuum leak

[Dmitry Tolstoy]

Good idea, will do the check at 2K rpm and report back.

[Dmitry Tolstoy]

Results:
At 2K rpm (actually rpm seems like it was a bit floating up and down around 2k, but that could be my fault)

First time 2k:
STFT = – 5.5%
LTFT = – 0.8%

Second time 2k:
STFT = – 10.2%
LTFT = – 0.8%

Idle:
STFT = 11.7%
LTFT = – 21.1%

[Richard Kirshy]

Numbers look better at speed…
Appears the computer is adding fuel in the short term and taking it away in the long term.
Might suggest you start with the simple things:
1 Try cleaning the MAF sensor with a approve cleaner
2 Try cleaning the throttle body

If that solves the issue ..your golden..
If not you’ll need to dig a bit deeper.
Could be a fuel pressure issue or injector issue
Next:
You might start looking for a vacuum leak.
There are several methods..
Smoke machine
Soapy water
Propane
Spraying brake cleaner ( be careful when attempting this one … Danger of fire starting)
But with a vac leak you should be getting higher numbers on both.

[Dmitry Tolstoy]

After a long digging, it looks like my model uses only MAP sensor combined with IAT. (got no MAF signal too)

Pulled it out, cleaned.
It was covered with what seems like oil/petrol mix.

Cleaned front area of the the TB plate. (it’s electronic, I didn’t want to mess with opening it by hand)

Had a try resetting the PCM / ECU and done the relearn procedure.
Disconneced the NEG bat cable, disconnected the POS bat cable, shortened them together for like a 10 min.
Although, I think I did it wrong and should’ve leave the POS terminal connected while shortening the NEG cable on it. (cause my radio channels memory stayed)

Results at Idle:
STFT = 1.6
LTFT = – 8.6

Results at 2K:
STFT = – 7.0
LTFT = – 4.7

2K results look worse than before, strange.
i’ll have to dig deeper.

fuel pressure? – if so, looks like too high pressure (possible raptured FPR / bad vac line)
I tend to belive it’s some vacuum leak.. don’t like this plastic intake manifold idea.

Any thoughts?

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[Rob]

Although, I think I did it wrong and should’ve leave the POS terminal connected while shortening the NEG cable on it. (cause my radio channels memory stayed)…. On some of the newer cars that is normal the radio stations are stored in EEPROM’s not reg memory and will last a resetting by pulling the battory… you can do a OBD2 readyness check or if you see a P1000 code in the pending or check engine codes then you reset the egine and its still learning it self.. wich is the P1000 code means…but if you had to reset the clock then you probly pulled the battory long egough to make the PCM relearn the car

ya I would check and clean the MAF… like he was saying…. I would also add that to check the lets call it the flapper I forget the correct name of it… there is a hole in it make sue that is clean…. that is the idel hole… and might be dirty… and I would also spry the throttle spring incause thats getting sticky and causing problems
ya I was thinking to myself that the hole is clogged a little because your seeing more of a problem in the idel or maybe a vacuum leak starting to form or some sencor is getting dirty
is the car running bad???… you might want to wait a day or 2 and recheck it… computer might still be releaning it self

[Dmitry Tolstoy]

As far as I see, this model lacks MAF, no supported sensor feedback.
Nor I could find it physically.

Updated info after driving around for about an hour today:

If vacuum leak, suspected areas:

Loose

later on i’ll water spray over marked areas + intake manifold,
I’ll Keep on update if any development occurs while testing out.

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[cj1]

Can you post map reading KOEO?
The combined LT/ST trims average around -10 . Was it closer to 0 at one time?
–

[Dmitry Tolstoy]

Idk if this tool has an option to give me such reading. (should be done via multimeter?)
by the way, I’m about 650m above sea level.. heard it could affect the map readings.

It was closest to 0 LTFT at 2k rpm, when my map was soaked in dirt. ( -0.8 ) [ fluctating STFT = -5.5 , -10.2]
afterwards best value was again at 2k rpm (3.9) [ fluctating STFT = -3.9 , -10.9]

Didn’t performed yet the water test.

[cj1]

With key on engine off, if scanner communicating then you should be able to read MAP,ECT, IAT before starting the engine.
MAP should read barometric pressure and on cold engine ECT=IAT.

Was wondering if the MAP reading is around 27 inHg, your altitude, with engine off.

[Dmitry Tolstoy]

Returned from a long drive, and tested with engine off as requested:

With engine off MAP is reading 27.8 inHg. (you were on spot :))
LTFT = – 8.6

[cj1]

LTFT 10plus/minus is close enough for engine to be running normally.
If MAP/ECT/IAT/RPM/TPS are within spec probably no much room for improvement.

Has the total -10 trim at idle been there all along or was closer to 0 at one time?

[Author]

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