2017~2024 Drop in mileage and performance?

[gman1]

I have about 42k miles on my 2018 CX-5 and noticed a drop in acceleration and mileage over time. The car feels lagging when I take it from a stop and is sluggish going up to speed. When I got a loaner for a 2019 CX-5 Non-turbo (which should be the same engine in my 18 CX5), I noticed a pretty big difference in feel and acceleration in that car which further makes me think something is wrong.
On the highway going 75-80mph from Dallas to Houston and back to Dallas, I was averaging 24mpg all highway which doesn't feel right compare to the 31mpg average I was getting on highway driving when I first got the car. I have done all required maintenance and changed out my air filter.
I wanted to see if doing the induction service may help restore my car close to the original feel and mileage. My dealership recommends a BG 3-part induction service for $150 or BG 2 part fuel/air induction service for $110. I think the 3-part induction service is just the BG 2 part with a bottle of fuel additives added in it. Does anyone know if it is the BG 44k or BG 44k Platinum fuel system cleaner that is added?

I have read in the forums that there is a warning in the manual that states "Never add fuel system additives. Otherwise, the emission control system could be damaged. Consult an Authorized Mazda Dealer for details" Does the manual then contradict what the dealer is selling?

Has anyone have any experience with adding BG in their gas? I use to add techron in my tank for my previous cars but the warning made me question if I can do the same with the CX-5. Thanks

 

[Nevada CX5]

I have not had a problem with Techron on my 18.

 

[Mazdiod2]

I have used Techron I got from Autozone and my car's still running. The tailpipes are a little sooty looking but I don't blame the techron. What else is wrong with your car?

 

[ruthrj]

Going 75-80 mph drops the gas mileage on my ‘13 2L several mpgs vs 65-70 mph. Gumout regane 3in1 fuel treatment hasn’t hurt every 10-20k mikes. My mileage has always been consistent. I’ve only experienced drops in gas mileage if driving faster than average or with a switch to winter fuel.

Using top tier or cheap gas? Tried a different gas station yet with a few tanks of top tier gasoline? I don’t think an induction treatment is going to be a quick cure. I’d try several tanks of good high quality gas and driving more conservatively before throwing money at it.

Sooting on the tailpipe normal to other poster. Typical with direct injection.

 

[gman1]

Going 75-80 mph drops the gas mileage on my ‘13 2L several mpgs vs 65-70 mph. Gumout regane 3in1 fuel treatment hasn’t hurt every 10-20k mikes. My mileage has always been consistent. I’ve only experienced drops in gas mileage if driving faster than average or with a switch to winter fuel.

Using top tier or cheap gas? Tried a different gas station yet with a few tanks of top tier gasoline? I don’t think an induction treatment is going to be a quick cure. I’d try several tanks of good high quality gas and driving more conservatively before throwing money at it.

Sooting on the tailpipe normal to other poster. Typical with direct injection.

I get gas from Costco or shell ( when I'm away from my Costco station). I have heard putting the transmission in 1st or 2nd gear and getting it up to 6000 rpm (redline) can help burn the deposit away. I have done that a few times but not sure if it helps. I have a bottle of techron but I'm cautious to use it since the car manual says adding fuel system additives can damage the emission control system.

 

[Nevada CX5]

I think the additive warning is a general disclaimer, not all treatments are to be used. Lucas cleaner is also safe.

 

[IamVAguy]

I get gas from Costco or shell ( when I'm away from my Costco station). I have heard putting the transmission in 1st or 2nd gear and getting it up to 6000 rpm (redline) can help burn the deposit away. I have done that a few times but not sure if it helps. I have a bottle of techron but I'm cautious to use it since the car manual says adding fuel system additives can damage the emission control system.

Did you have the recall done for the PCM reprogramming? I recall the dangerous cylinder deactivation thread where the OP was revving his engine up to 6000 rpm and experienced the no power situation.

 

[ruthrj]

I get gas from Costco or shell ( when I'm away from my Costco station). I have heard putting the transmission in 1st or 2nd gear and getting it up to 6000 rpm (redline) can help burn the deposit away. I have done that a few times but not sure if it helps. I have a bottle of techron but I'm cautious to use it since the car manual says adding fuel system additives can damage the emission control system.

Italian tuneups that you describe may help, it all depends on your driving scenario. Short trips, low speed driving and stop and go traffic can cause buildup on the intake valves. Longer drives On the highway with higher sustained rpms would be ideal to preventing build up. I’ve nearly always driven under ideal conditions and continue to find myself in that scenario. I’ve been getting 34-35 mpg this week with my 2L driving 20+ miles doing 50-60 mph (nearly nonstop).

I cleaned my intake valves at around 70k miles following FelixDs YouTube video and I think it helped the feel of the engine a bit. Purrs like new at idle vs some slight vibration but required a lot of effort removing the intake manifold and physically cleaning the valves. The deposits on the valves were soft and dissolved easily with B12 chem tool. I’ve never experienced a drop in gas mileage though so I really didn’t gain anything after the cleaning. Throttle body was very clean during the disassembly procedure but cleaned it too for good measure. Also cleaned the MAF with the appropriate cleaner.

I’m assuming with +40k miles and the highway driving you describe that you likely shouldn’t have a ton of crud on the intake valves. Maybe you have some deposits on the injectors but thankfully Costco is listed as a Top Tier fuel provider. I’d try a bottle of Techron concentrate, gumout regane or whatever has PEA in it. An added measure could be an application of CRC intake valve cleaner past the MAF. Give the oil a change after the gas tank and intake manifold cleaning. Id be a little wary of the CRC though. I much prefer removing any crud By hand vs letting it ping around within the engine, but that’s my 2 cents.

Again though, id try simple stuff. Slow down a bit, higher speeds kill gas mileage. Run a few tanks of good gas with a bottle of fuel system cleaner. Check your tire pressure (run it a little over the sticker pressure, say 2psi higher). See what kind of boost that gives to gas mileage before taking more drastic measures.