To start – I own a Dacia Dokker 2018 with 1.6L 16valve H4M (HR16DE) engine that in EU holds “EURO6” emissions norm! Engine has done little over 90 000Km and as there are no fault codes stored in engine module or any other modules in the car.
Fuel Economy (combined) is 7.2L of petrol per 100Km that is when I dive with fuel economy on mind, if driven normally or with A/C on consumption goes to 7.5 to 7.7L of petrol per 100Km! This is a lot of fuel for 1.6L engine that produces only like 100HP and complies with EURO6 emissions standards!
I have been experimenting and testing ways to find cause and solution to solve this unusually high fuel consumption with my engine and OH boy I have done some crazy things …. I also started to monitor Fuel Trims and O2 sensors readouts – For this car and engine fuel trims are all over the place! I assume it is caused by missing MAF sensor(engineers didn’t decided to use one). O2 sensors : Sensor 1 is wide band and it mostly showed lambda ( it reacted and adjusted mixture well ), however S2 did showed bit richer condition than I would like (when lambda on O2S1 then O2S2 was on 800mV – range from 70mV to 970mV). Lets start with checks and service : I have done oil change including oil filter, replaced air filter, spark plugs, fuel filter, I have cleaned fuel pickup filter, removed and cleaned injectors, cleaned PCV valve, cleaned and relearned throttle body, measured fuel pressure at fuel ramp (measured 3.5bar), measured exhaust system back pressure ( removed O2S1 and measured no pressure while reving the engine. Now lets jump to mods … tested lifting fuel pressure to 4bar – as same engines in Nissan cars are having 4-4.5bar of fuel pressure. This resulted in bit more negative fuel trims but did nothing to fuel economy or performance, so I have decreased it back to 3.5bar. Next I have removed factory air intake (note: this car/engine doesn’t have MAF sensor) I made sure that air entering engine was filtered to some degree but it was as free breathing as possible …. went for drive and no change in fuel economy or performance (there was just increased induction noise).
Previously mentioned O2S2 higher readout (richer mixture at O2S2) got me thinking that car is set to run richer – that could explain higher fuel economy! So I got couple of O2 sensor stand-offs spacers things …. Stay with me as I cut out end of them and installed stand-off O2 spacers under both of mine O2 sensors – Yes you heard right O2S1 and O2S2 is now mostly out of the direct exhaust flow in exhaust pipe!
Now This is not standard use case for those stand-offs …normally you use them under O2S2 when your catalytic converter doesn’t work properly. But here in my case it moved both of my O2 sensors out of direct flow of exhaust gasses and it resulted in O2S1 detecting slightly richer air/fuel mixture (as less air particles were hitting the sensor) so Engine computer adjusted mixture to compensate this new situation and it resulted in lover fuel economy to be precise it is now at 6.5L of petrol per 100Km (with normal drive without A/C) that is huge difference and so far I have done over 5000Km and noticed no difference in performance and also no fault codes from any of the engine/car modules. Before you start overthinking about … running lean can cause this and that …think about fact it was running richer and what could cause that. Also even if my mod does make it run leaner we talking slight difference that has no effect on health of the engine. Also I have monitored reaction times of both O2 sensors (as they are out of direct flow of exhaust gasses) and they both acting accordingly to changing air/fuel mixture!
Bonus: Engine can exhaust gasses slightly better as both O2 sensors are almost entirely out of exhaust pipe-they are blocking exhaust pipe less!