Ford focus - engine code po170

[munimpatel]

Hi I have a ford focus 1.6 auto 2000 reg. The engine management light has come on and shows p0171 code - fuel too lean.

The scanning tool shows the following:
Calc load: 20%
Cooltent temp: 106 degree
stft b1: 32%
ltft b1: 3%
Engine speed: 800 rpm
spark adv: 12.0btdc
IAT: 29 degree
MAF: 1.5 g/s
TPS: 18%
02sl: 1112
02s 11: 0.2 - 0.7v
shrtft 11: 32%
02s 12: 0.67v
shrtft 12: 99%

freeze frame:
stft b1: 0%
ltft b1: 25%
stft b2: 0%
code triggered: p0171

These readings are based on car being idle after being driven for 20 mins.

In addition when I rev the engine to 1500 rpm and hold for 30 seconds : the LTFT is below 7% but the STFT comes down to about 15% from 32%

When I rev engine to 2500 rpm and hold for 30 seconds: Both STFT and LTFT are below 5%.

So far I have done the following:
changed: engine oil, oil filter, cabin filter, air filter, spark plugs, coil pack, coil leads.

I am thinking it might be a vacuum leak? any ideas?

[elliotff]

Fuel Filter ?

[kev b]

Try spraying carb cleaner around the intake hoses, if you have a leak the revs will rise or fall. You could unplug the AFM and see what happens, maybe give it a spray with carb cleaner.

[munimpatel]

How do I test the MAF sensor? too make sure it is good. I have a scanning tool. what reading should I be getting at idle and at 2500rpm

[Chirpsean]

It does sound like an air leak could be a possibility. To check the MAF you really need a scope to check the output signal but you could try with a multimeter. At idle the maf should output about 1.5v climbing to about 4.5 if you rev the engine quite hard. As i said a scope would show you if there are any dips/drop out etc.

[shoehorn]

It is more than likely to be the `handlebar` breather pipes that join the two halves of the manifold to the crank breather.
These pipes collapse and split,they are around fifteen quid from Ford and are a push fit.

If you look between the 1-2 and 3-4 branches of the inlet manifold you will see 2 rubber pipes that join to the inlet manifold flange and then meet in a plastic tee then carry on to a push in breather valve a little lower.
A bit fiddly if you have hands like mine but easy even for a novice with a pair of long nose pliers.