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Advice regarding correct MAP sensor values

Discussion in 'Gen 3 Prius Technical Discussion' started by Saqib Tahir, Jun 15, 2024 at 9:22 AM.

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  1. Saqib Tahir

    Saqib Tahir Junior Member

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    I have a 2011 Prius with 230,000 km on it. I am getting poor mileage and a P0171 code. I did some research and got a cheap J2534 cable and Techstream to get started, following the repair manual. My O2 sensors seem fine. I did a fuel injection volume control test for AFS, and both sensors gave appropriate readings depending on the fuel injection volume, so I think they are alright.

    I read the freeze frame data, which showed the LTFT at 28% and STFT at 16% at idle. I also did the EGR valve control test, but the MAP value was at 60-70 kPa at an idle RPM of 1000 in maintenance mode. When I opened the EGR valve to step 30, the MAP value dropped a little bit instead of increasing. The engine became slightly rougher, although it was already having a rough idle but not terrible.

    I am new to all this, and mechanics in my area are not very helpful in situations like this. What should I do next?
     
  2. Eddie25

    Eddie25 Active Member

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    Personally I'd want to see a graph of the short term fuel trim numbers while driving (as they relate to RPM).

    What does the MAP read when the engine is not running?

    MAF readings at different RPM's could be useful as well. The MAF is also pretty easy to visually inspect if that hasn't been done.
     
  3. ChapmanF

    ChapmanF Senior Member

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    What's the MAP reading when the engine is stopped? Should be reasonably close to your local weather station's barometer report.

    60-70 kPa looks high for normal idle. But there are times when the Prius engine is turning at idle speed, but doing work (the car is using it to charge the battery). At those times, the readings will not be the same as for true idle.

    30 steps is pushing the maximum you would ever want to open the EGR valve for a test (the wording in the repair manual is, in fact, "Do not open the EGR valve 30 steps or more during the Active Test"). The manual does expect the MAP reading to increase at least 10 kPa above its idle baseline when you do that. But, again, the reading you saw earlier might not have been the idle baseline.
     
  4. Saqib Tahir

    Saqib Tahir Junior Member

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    When the engine is not running, the MAP value is the same as the atmospheric pressure value at 97 kPa.

    I have checked the MAF sensor, and it was very clean, so I didn't feel the need to clean it again.

    I have been driving the car since then, and the P0171 code has not reappeared. However, the MAP value is still high for idle according to the service manual.

    Driving data and idle in maintenance mode after an hour of driving with the battery half full is attached.

    My concern is that I got 20 km/l (47 MPG) on a 50 km trip from work to home. My workplace is in a different city, but it's not on the highway. The roads are small with lots of curves, so I'm not driving at a steady speed, but I tried to maximize efficiency by cruising and letting my foot off the gas momentarily, then keeping it in EV range for as long as I could.

    However, as soon as I am in my hometown, mostly making small trips to grocery stores and back, my average drops significantly. On the same record trip, I drove another 30 km, totaling an 80 km trip, and my average dropped to 10 km/l (23.5 MPG) from 20 km/l (47 MPG). This makes me think that at idle, it's consuming more petrol.

    What should I do next?

    driving data 2 .jpg driving data.jpg idle maintenance mode.jpg
     
  5. Saqib Tahir

    Saqib Tahir Junior Member

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    I was waiting for engine to start rough idle or increase MAP value by 10 KPa but didn't happen untill i reached near 30. Only engine was rough but map dropped instead of increasing. I did and map value with battery full but is still high then 40 uper limit.