2019 Infiniti QX50 CVT: Sudden drop in MPG + change in engine noise — no codes

I’m seeing a sudden, significant (>40%) drop in MPG from my 2019 QX50 (FWD, CVT). I do a fairly regular long drive from SF to Sacramento, and highway MPG for these trips has always been ~31-33MPG; city MPG is more variable, but usually in the low 20s. Now, for the same SF-Sacramento drive, I’m only getting ~22-24MPG; and city MPG is in the 10s.

Events that might have caused it

This all seemed to happen after either/both of these events during our last road trip (they happened on the same day so it may be either, or maybe neither and just coincidental):

  1. We were cruising on Neutral for about a mile at ~70MPH (which the manual said we’re not supposed to do)
  2. We were driving on a fairly bumpy, unpaved road for a few miles.

Other Symptoms

In addition to the drop in MPG, I also noticed these symptoms:

  • The engine sound is noticeably louder when the vehicle first starts, and when the vehicle is in reverse. It’s not abnormally loud, but definitely louder than normal, and the pitch is low.
  • At over 80MPH, the engine is slightly louder than normal–almost like it’s running on a lower gear than it should. However, I can put it in the highest (simulated) 8th gear (transmission is CVT but has paddle shifters) and behavior is the same.
  • When driving at normal speeds, engine sound is mostly normal.
  • There was a slight burnt smell from outside the vehicle (can’t smell it inside) for a couple of days after the events above, but the smell is now gone.

Dealer says nothing is wrong

A few days after the events above, I took the car to a remote dealer (while on our road trip). The dealer said they ran diagnostics and did a test drive, but found nothing wrong. Computer returned no codes. He said the weird behavior may be due to a change in elevation, and everything should be back to normal when I get home.

I was hoping that may be the case, but of course now I’ve been home for a few weeks, and I’m still seeing the same low MPG, and louder-than-usual engine noise.


  1. Can the drop in MPG be related to the change in engine noise?
  2. Can I have damaged the transmission while cruising on neutral, causing the symptoms I described?
  3. Can something have popped loose during the bumpy ride, causing the symptoms I described?
  4. Because the increase in engine noise is rather subtle, it’s easy for them to overlook, but I’m pretty sure it’s real. Any suggestions on what I can look for myself? And if I take it to my local dealer, what specific things can I ask them to check this time?

More info

  • I cross-checked my MPG numbers with both the onboard computer and my own calculations at the pump, so I’m very confident in them.
  • The car is ~2.5 years old with 18000 miles.
  • I checked the engine air filter, and it looks OK. Also checked tire pressures and they’re in range.

I would take it to a dealer near you and get it looked at again.


I would say a definite YES to number 1 and number 2. Why would you coast in neutral? I would guess your CVT is now fried.


This is a wild guess, but maybe disconnect the battery for a few hours and let the ECU reset itself.
I have a feeling the Neutral cruising, reset something in your idle control and the transmission ratios.

What do you mean 'If ’ you take it to a dealer . That is why you have a warranty . And no you don’t ask them to check anything or replace something. You give as good of descrition of the problems as you can.


Is motor turning at same rpm at highway speed as before? Do you recall what rpm was before?

Might you have damaged the exhaust system? That could do this.

What do you mean 'If ’ you take it to a dealer . That is why you have a warranty . And no you don’t ask them to check anything or replace something. You give as good of descrition of the problems as you can.

I already took it to a dealer, and gave them the description that I wrote here, and they said “everything looks fine.” So I suspect that if I do the same thing all over again, they’ll just give me the same response. Hence I feel like I need to provide some pointers to them this time for a better chance of a better outcome.

Is motor turning at same rpm at highway speed as before? Do you recall what rpm was before?

I don’t remember the exact RPM numbers before, so can’t really compare, unfortunately. The current RPMs are in the mid-2000s at ~75mph. Seems a bit high maybe but I really can’t say whether it’s higher than before.

If any of the fluid pumps in the transmission are driven by the input shaft, you likely damaged it by doing something the manual said NOT to do. Why did you do that? It is very possible that the tranny still functions but is internally damaged.

Wasn’t that dealer on a trip and not your local dealer ? It may not be the proper responce but most mechanics and service writers will get annoyed if you tell them that someone on the web said it was ( put part here ).

Example: I have a little better than basic understanding of small gas lawnmower type engines . My neighbor could not get his mower to start . I started going through my check list to find or eliminate the problem . He started telling me that what I was checking was not the problem . Well it was and the thing ran just as it should. I never helped him again .

If it’s in fact the transmission, would the computer show anything or return any codes? And would there be other symptoms? (The transmission seems smooth as usual, and I’ve noticed no other anomalies with it.)

Also, how would they go about finding out if that’s true. (Since there are a million things that could cause this, I don’t want to prime them and tell them to take apart the transmission or replace if something else could also be the problem.)

If the dealer can’t find anything wrong, They won’t replace the transmission under warranty just because you told them to.

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You tell them the symptoms (mpg drop, etc.). It’s the techs’ job to figure out the cause. If you get no satisfaction, elevate it to Infinity corporate. Something like this may (or may not) show up in a computer scan.

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I think this did it! Disconnected the battery for a couple of hours this morning, then took the car out and drove about 20 miles on the freeway. MPG according to the computer is now 34, but I’ll double-check next time I gas up.

Engine still sounded loud the first time I started it after the reset, but on a second start it sounded fine. I’ll keep paying attention to it. (And who knows, maybe the engine noise thing is all in my head.)

Thank you so much for the suggestion!

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That cleared the average fuel economy memory, how often do you reset it before a new trip?

If you clear trip computer you will get a good number in 10 miles. If you get 32 mpg today and got 22 mpg 2 days ago, then there was an issue. Do I think you are getting 32 mpg? No, but if you drive the same 10 mile route to work everyday you should get the same mpg everyday. Generally speaking.

I reset it manually every time I hop on the freeway.

Just reset everything on the readout at refueling . That is the only way to really know what you are getting.

If the poor mpg problem returns, I’m thinking you may have a leak in your exhaust system. That would explain the increased engine noise, and it could also explain the drop in mpg. An exhaust system leak prevents the engine computer from providing the correct air/fuel ratio.

I doubt the coasting in neutral did anything adverse, but the bumpy, unpaved roads could have shaken the exhaust system and created a leak.