Fuel Mileage Woes on NX w/72K miles
07-14-19, 08:26 PM
#17
Intermediate
All turbocharged engines require spark plug change at 40K miles. At least it was the case with my Audi and now with NX. Friend of mine has MB and it is the same service requirement for spark plugs. As far as I understand, this is due to turbo engines having higher compression ratio and running hotter ignition.
07-16-19, 11:42 AM
#18
Rookie
Thread Starter
The stock plugs were not extremely dirty/worn but the tips were clearly in need of replacement. I strongly believed this was going to make a difference but it did not. I will buy a non K&N filter and see how that goes. I really like my NX but with the amount of driving I do and cost of Premium fuel (especially here in CA) sometimes the thought of a Rav 4 Hybrid (over 650 mile range) ponders in my head.
08-02-19, 06:06 AM
#20
Driver School Candidate
Gulshan is right. Carbon buildup is an issue with most turbos and you should flush the intake and fuel injectors. Just had mine done at 40k miles with spark plugs....ill tell you....its was dirty and deffinetely improved every aspect of the car from performance to handling and acceleration. Its 200$ at the dealership or buy techron and use it as directed.
08-03-19, 11:44 AM
#21
Intermediate
Gulshan is right. Carbon buildup is an issue with most turbos and you should flush the intake and fuel injectors. Just had mine done at 40k miles with spark plugs....ill tell you....its was dirty and deffinetely improved every aspect of the car from performance to handling and acceleration. Its 200$ at the dealership or buy techron and use it as directed.
Also, I do not want to imply anything, but how did changing spark plugs and, supposedly, removing carbon buildup made your car handling better?
08-05-19, 05:08 AM
#22
Lexus Test Driver
Those $200 dealer fuel system carbon cleaning jobs are such rip off, all they do is shot some techron like product into the intake, kind of like what some people do to their lawn mowers. It is not a complete valve cleaning job and certain does nothing for handling. As far as i know, the nx’s engine has a dual injection system which keeps the intake valves clean. Other areas can still have carbon build ups but at a much slower rate.
08-05-19, 07:44 AM
#23
You either have to mechanically clean intake valves, like ETCG does, or sand blast them with walnut shell stream. Why that, I do not know, maybe it's hard yet not abrasive for the job.
Last edited by ukrkoz; 08-05-19 at 07:54 AM.
08-05-19, 08:02 AM
#25
According to this https://www.caranddriver.com/news/a1...ect-injection/ both port and direct injection are used during low to medium engine load and rpm.
D-4ST uses a high pressure fuel system for injection directly into the cylinders and a low pressure system for port injection. Injection is split between the direct and port injectors according to engine load, optimizing fuel combustion in all driving situations to improve both low-speed torque and fuel economy.
https://blog.lexus.co.uk/lexus-nx-20...ine-in-detail/
With separate twin injectors for both direct and port injection, ESTEC D-4ST could perform high-pressure direct injection into the cylinder and conventional intake port injection, or direct cylinder injection only, according to engine speed.
https://en.wikipedia.org/wiki/Toyota_AR_engine#8AR-FTS
I stay corrected, thank you for pointing out and making me better research this.
Posrt injectors=cleaning valves - it at low engine RPM/non turbo conditions. High engine RPM/turbo boost quickly shifts to direct injection only. So if you are a fast driver, you have less cleaning done to your valves.
Last edited by ukrkoz; 08-05-19 at 08:23 AM.
08-05-19, 09:09 PM
#26
Currently have 72K on my 15 nx F-Sport... Yeah I drive a lot, I know. I started noticing my range getting lower and lower and noticed I was filling up more often. When I first got my NX 4 years ago I had a range of 330 to 340 miles on a full tank. I averaged anywhere from 23 to 24 MPG with about 50/50 city/hwy driving. I replaced the original spark plugs with OEM ones a couple of thousand miles ago and this had made no improvement at all. All my tires are inflated to 35, no check engine light, car runs perfectly fine, and my K&N air filter is nice and clean. Any thoughts where else I can check ? Is the engine just "wearing out" and not being as efficient as before? I filled up this morning and my range was at 297 miles. I've always used premium gas and kept up with full synthetic oil changes every 10K. I drive like an old man and my car rarely touches 4K on the rev meter... What gives?
Also, it might be time for you to have a major tune up. Did you have your 60k tune up?
08-06-19, 09:52 AM
#27
Rookie
Thread Starter
I haven't done the "60K mile tune up" but I have changed the plugs and air filter. There really isn't anything else I can think of that is user serviceable. The tires all are at 35 PSI and the car runs great. Idles just fine. I will probably end up getting some fuel additive on my next fill up and see if that makes any difference. The car also developed a rattle on the hatch's OEM spoiler deck that is driving me crazy. I take great care of my NX and these little things are beginning to bother me.
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