High Fuel Trims?

[Sam9978]

Yea, that sounds good. At least the throttle body cleaning isn't too difficult. Just a note here about that. I replaced the throttle body gasket when I cleaned mine. The OEM Mazda was priced around $20. A Beck-Arnley brand I bought online cost $3-$4 plus shipping. It was identical, even made in Japan as the original. But, the original could have been reinstalled since it was still so resilient-- silicone gasket.
I think you'd do well to address the items that make it run smooth and contribute to reliability and not get too freaked out about LTFT values. As the old saying goes-- "Drive it".
And speaking of running smooth, have the spark plugs been changed? Mazda recommends plug change at 75K miles for my CX-5. I changed them at 71K a few months ago and am still loving the improvement in smoothness and stronger pulling out. Not huge but nice improvement.

Thank you.

Yes, I'll probably get a gasket at Rock Auto or Autozone, if similarly priced, just in case I need it.

Spark plugs were changed in April 2023 at 74K.

I guess I'm a little "freaked out" about the fuel trim as my daughter got a 2016 Hyundai with 80K and the trims were going between +12 to +17. I couldn't find anything wrong nor could 2 different mechanics so I decided to not spend any more money on it and about a month ago we got a cat below threshold code. which is rather expensive to fix. So it left me a little leary of just ignoring out of wack fuel trims. The "good" news is that someone sideswiped her and the car was totalled (no one was hurt) and the insurance payout was the same amount we paid for it 2 years ago so it all worked out in the end. Of course I hate having to look for another car so there's that as well.

 

[Jmaz]

Thank you.

Yes, I'll probably get a gasket at Rock Auto or Autozone, if similarly priced, just in case I need it.

Spark plugs were changed in April 2023 at 74K.

I guess I'm a little "freaked out" about the fuel trim as my daughter got a 2016 Hyundai with 80K and the trims were going between +12 to +17. I couldn't find anything wrong nor could 2 different mechanics so I decided to not spend any more money on it and about a month ago we got a cat below threshold code. which is rather expensive to fix. So it left me a little leary of just ignoring out of wack fuel trims. The "good" news is that someone sideswiped her and the car was totalled (no one was hurt) and the insurance payout was the same amount we paid for it 2 years ago so it all worked out in the end. Of course I hate having to look for another car so there's that as well.

Sounds like you're pretty much on top of things. Keep us posted here. Good luck!

 

[Sam9978]

My friend helped me clean the valves and throttle body Friday evening. It was surprisingly simple to get the intake manifold off and get to the valves.

The valves were definitely dirty though I'd say the carbon buildup was more gunky than the hard carbon deposits you usually hear about but either way, they were pretty dirty. There was also a LOT of oily liquid and residue all over the inside of the intake manifold so much so that it was dripping out when we turned it over. It was much more liquid than oil but the same colour and smell.

We also cleaned the throttle body, MAP, and MAF sensors while we were at it and also replaced the PCV valve.

I took a few pictures which I will post for your interest. I couldn't get a good angle and I don't like holding my phone with dirty hands so just took a few.

I reset the averages before heading home and I hit 38.7 MPG on the way back. Granted, it was almost perfect driving conditions for getting good mileage; 40 to 45 MPH, no traffic at all so no slowdowns or stopping at all for almost 10 miles. I reset the averages again so I can see what I get around town now. The engine also seems a little quieter and like it has a little more power.

One odd thing I noticed is that the MPG on the dashboard and the trip MPG on the infotainment system sometimes read wildly different averages. They both reset at the same time and by the time I got home and stopped the car there was a 2.5 MPG difference if I remember correctly. I'm going to assume the one on the instrument pannel is closer to correct.

Sadly my fuel trims are still too high but I know it can also take up to 200 miles for the ECU to relearn so I'll try to be patient and if they still aren't closer to normal after 200 miles I might try disconnecting the battery and see how it goes.

 

[Sam9978]

My fuel trims are steadily going up. They were between +6 and +10 up to and over the weekend through yesterday but today they went all the way up to +18 for a bit but then settled around +16. I know that is very bad for a CAT, and other things too I'm sure. I'm wondering if the MAF sensor is bad as it seems to be reading high but I'm no expert.

I tried disconnecting the battery for 30 minutes which, from my experience with other cars, will make the trims start back at 0 but when I started the car up it stared at +15 immediately. Does anyone know how to reset this to default?

I guess I'll see about having a vacuum leak test done and go from there unless anyone has any ideas of something I can try.

I've attached a video of a screen recording from a drive this afternoon in case anyone sees anything of note.