Polo 1.2 (CGP) System too lean (bank 1)

[Kalz0387]

Hey everyone,

Unfortunately I have a system too lean (bank 1) on my ‘10 reg 1.2 Polo (CGP engine).

I’m new to vehicle diagnostics but have been reading around a little about this problem.
I have already asked in the VCDS forum for some help to scan the Short and Long Term Fuel Trim values .

Are there any quick and easy checks or things I can do whilst waiting for some help on the diagnostic side?

i have recently added some redex petrol system cleaner to the car and used a more premium fuel in case it is blocked injectors. I need to run the car some more miles I think before seeing any results from that (if that is the problem)

anyone have any similar experience/suggestions?

[Crasher]

That suggests an inlet system air leak such as a vacuum hose detached or split.

[Kalz0387]

Hi Crasher

Hope you're well.

Yeah - that definitely seems to be one of the things to check...one of the other suggestions seem to be:
- Faulty MAP

I managed to get hold of an OBD scanner to measure some data. I took some MAP readings, and fuel trims for different RPMs.

1. MAP data

(i) before turning the engine on - reads 14.5psi which seems about right when compared to today's atmospheric pressure which was around 14.6psi
my thoughts: MAP sensor is ok.
But are there any other readings/tests I can do to confirm if the MAP is definitely ok? maybe compare how the MAP varies with load factor and throttle position %?

2. Fuel Trim Data

(i) I took the Short Term and Long Term fuel trim % values over time (car stationary and just held different rpm constant for around 30 secs). You can see the results below..

IDLE -

Attachment 36870

1500RPM -

Attachment 36866

2000RPM - about 30 secs

Attachment 36867

2500RPM - about 30 secs

Attachment 36868

3000RPM - about 25 secs (RPM dropped automatically to idle before 30 secs)

Attachment 36869

Observations:

- Long Term Fuel Trim is +11% or thereabouts.

- Short Term Fuel Trim is moving around a bit:
at idle it seems within acceptable level
mid rpm (1500 and 2000): starts to get a little worse (more negative) with higher rpm
at the high rpm (2500 and 3000): seems to be within an acceptable level again.

I'm not entirely sure what to make of it?

p.s. I am very new to all this but quite happy to learn/research as I go along.

[Crasher]

The long term fuel trim is too high confirming it is running too lean IF the lambda sensors are telling the truth, they don't always. First look for an inlet air leak but also check the exhaust flexi as these can crack, allowing oxygen into the system before the second lambda sensor which can make the ECU think the combustion is lean when it isn't.