Engine running rich triggering CEL
 

2005 2.4 T5
So after a few trips, ive got another CEL:

ECM-120D - Air Mass - signal too low
ECM-216D - Long term Fuel trim - Signal too low

So it indicates that the car is running rich? (which in my mind means it cant be a vac leak????) - looking at the trims on the snapshot, shows LTFT at -13% and STFT at -6%

Anyone got any ideas where to start on this?

Thanks

The engine has a number of sensors that it can fall back on if one is duff or reading an unexpected value. For example the HEGO sensor will allow trimming of the air fuel mixture even if the detected air flow is wrong so as to ensure the engine keeps running.

For a given engine speed the car knows how much air should be coming in; if due to a vacuum leak, that mass is wrong, you will get detected low air mass, quite correctly. It could be a MAF sensor, it could be a thousand things, but I would be checking for leaks first.

Bit of an update on this.. still (slowly) tracing the issue.

Took the TB off and gave it a damn good clean - it needed it!
The idle surging is now much reduced but still an issue occasionally..

So by my rekoning, next on the list to check (im determined not to start firing the parts-cannon without good evidence!)

fuel pressure/injectors
MAF
HO2S
Coils


I replaced the plugs and looked at the state of the old ones to try and get an idea - to my eyes it looks like the engine is running lean?? - 2,3 and 5 plug wells were submerged in oil which is why those look wet.

Edit to add: pcv needs doing too, but again would that cause a too rich code?

I've recently changed my plugs for a routine service. A couple were submerged in oil which I struggled to see where it could be coming from. Turned out the rubber seal on the filler cap had split. A quid off ebay sorted it :-)

pcv would result in oil buildup so might be worth a shot - allow a full day - intake manifold off

Just another update.

After an experiment of unplugging the MAF showed the car actually ran better, i thought id take it off and give it a clean with archoil.(nothing to loose at this point)

Im happy to say that it seems to have had some considerable improvement so far... the car feels much more responsive and smooth - as much as it can be with the auto 'box... and monitoring the fuel trims it seems happier with much lower numbers so no more codes yet..

I did buy a fuel pressure gauge kit off ebay to test FPR and injector leakage, however the schrader valve attachment broke so that test will have to wait.

Will monitor how its running over the next couple of weeks (im using torque-pro app with blutooth adaptor for day to day monitoring and vida for more in-depth stuff)

Another update - Car is still running "well" with no more codes stored.

Long term fuel trim has stabilized round the -7% so still running a bit rich.

Monitoring vacuum/boost via the torque app seems to show that under hard accelleration, im only getting ~8psi of boost, although i am also doubting the numbers as shows a peak of almost 20psi.

Next step i think will be to get a cheap mityvac to start testing the small boost pipework and wastegate pressure.

I also need to man up enough to start doing gearbox sump-dumps, even though itll be a PITA as the R-style airbox on this model T5 is conveniently right over the top of the gearbox dipstick port..

have a check on the rubber hose on the turbo inlet side...where the oil re breather joins...just make sure the rubber hasnt gone soft and either holed or split, allowing the turbo to suck air in from here rather than all the way from the filter& maf. bit of a wild card, but happened on one of mine. :)

my 2.4 t5 also runs at -7 long term ft, so presume its normal?