Increased fuel consumption — what's the reason? INFINITI FX 4.5 Allrad (232 kw / 316 hp) (01.2003 - 12.2008)

First thing I’d check is spark plugs and coils. On the FX S50, weak spark gives more fuel waste than you’d guess. My buddy had same symptoms, swapped all plugs and his consumption instantly dropped by 2L/100km. The next culprit: mass airflow sensor or lambda sensor – dirty or old ones mess up air/fuel ratio, cost you extra fuel, and rarely throw codes right away.​

Had a similar jump in fuel use after a cold snap. Replacing a half-stuck thermostat (engine was running cold too long) brought my numbers back down. Cold-running engine kinda guzzles fuel because ECU over-compensates.​

Don’t ignore injectors. After 100k miles, mine started dripping at idle and I was up to 17L/100km! Pulled and cleaned injectors, replaced seals and noticed improvement—idle got smoother and computer showed 14.2L a week later.​

One thing people miss check your tire pressure every couple of weeks, especially with temperature swings. If you’re low by just 0.2 bar, it adds up in fuel. I drive mostly city, and just bumping pressure back to spec cuts half a litre off the average.​

If you ever see rough idle or weird revs on startup, it might be the start of valve/camshaft wear or oil burning—FX V6/V8 engines can develop these after 120,000 km. Don’t let oil get too low: can cause all sorts of problems including higher fuel use.​

If your driving changed recently (more short city trips, lots of idling, or aggressive throttle), it’s normal for the consumption to go up, even without anything being broken. But definitely check air filters, simple and cheap fix.​

Removing the catalyst or having it clogged can spike fuel use. I bought my FX after the previous owner had “gutted” the cat, and fuel consumption never returned to normal until I fixed it.​

bad fuel or winter blends (lower energy content) usually mean a jump in consumption during colder months—happens every year in my experience.​

.Online Routine diagnostic scan isn’t a waste of time on older FXs. Mine once had a dodgy sensor that didn’t throw a check engine light at first, but was feeding the ECU wrong info and over-fueling as a result.​

aggressive driving with hard acceleration easily adds 2 L/100 km on these engines. When I switched to a calmer style, combined mileage dropped close to the spec.​

I always start with the basics firs fresh plugs, new air filter, clean the throttle body, proper oil change. Covers 80% of fuel consumption problems and doesn’t cost much if you do it yourself.​

Bought my FX at 160k, former owner never changed the spark plugs...after doing a full tune up, consumption dropped from 18L to 14L instantly. So yeah, I’d check ignition components first thing.​