MPG Drop to 35 MPG after New Battery, EGR Overhaul, and Tires (2010 Five/Tech)

Hi Mendel, thanks for following up.

Regarding the MAF cleaner: The 'household dry cleaner' I used was a generic solvent I checked my LTFT (Long Term Fuel Trim) today at a warm idle in Park, and it is sitting at +6.25%. Given that it’s positive, do you think the cleaner left a film that is causing the car to over-fuel slightly?

Regarding the 12V Battery:

• The sticker on the battery is A23, so it is exactly 3.5 years old (Jan 2023).
  
  
• The shop tester showed it hit the rated 325 CCA, but noted the State of Charge was only 66%.
  
  
• My multimeter shows 12.42V at rest, but the dash menu shows it dropping to 10.9V - 11.1Vas soon as the car enters IG-ON mode (load).
  

Tire Update:
I confirmed they are 215/50 R17 Bridgestone Turanza QuietTracks. My previous set was 215/55 R17. I've set them to 38 PSI Front / 36 PSI Rearto stay safe as suggested.

Since I have a 111% hybrid pack and a clean EGR, do you think that +6.25% trim and the 11.1V load drop are enough to explain the drop to 35 MPG, or is it mostly just the rolling resistance of these specific tires?

 

Thanks for the chart, bisco. It’s very helpful for comparison.

To clarify my car's behavior: My engine does shut off at stoplights as long as the hybrid battery has a sufficient charge, so the hybrid stages (S4) seem to be working.

However, my voltage still shows a significant drop based on your chart:

• 12.42V resting (Multimeter) = ~75% Charge (Green Zone).
  
  
• 10.9V - 11.1V under load (Dash) = <10% Charge (Red Zone).
  

I've also checked my LTFT, which is sitting at +6.25% at a warm idle.

Since the engine is cycling off correctly at lights, but I'm still stuck at 34.6 MPG (Trip A reset this morning), it seems my fuel is being lost while the engine is running. I suspect it's the combination of the +6.25% fuel trim and the rolling resistance of these 215/50 R17 QuietTracks. I've set them to 38 PSI to see if that helps.