Code P0172 - Engine Running Rich

Hi guys,

I've been having problems with my 2012 Suzuki Jimny Sierra. It has a standard M13A engine.

Initialy, a check engine light was triggered. Freeze frame data revealed that the engine was at idle when it exceeded threshold for fuel trims. The LTFT was at -14.8 and the STFT was at -20.4.

When at load, the LTFT reduces to between -7.8 and -13.0. The STFT either zeros or becomes lean (around +7).

All four spark plugs are fouled.

My first thought was excessive fuel pressure. I tried my luck at changing the fuel pressure regulator on the assumption that it was stuck closed.

The results were significantly better. The LTFT went down to -7.8 and the STFT zeroed.

But, around a week later the fuel trim returned to running rich.

I'm suspecting clogged fuel injectors, restriction in the return line or an EGR issue. I used opal fuel (low quality 91 octane) for a year. Perhaps that depositied gunk in the injectors.

What do ya's reckon. Any advice would be greatly appreciated.

Check for a cracked exhaust manifold or a leak that would cause a false reading from the O2 sensor.

If there are no leaks, swap out the oxygen sensor on the manifold, when this goes out of spec it causes over fuelling.