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Thread: Engine Hesitates going from Light to Moderate Throttle

  1. #1
    Join Date
    Oct 2013
    Location
    NovaScotia Canada
    Posts
    10

    Default Engine Hesitates going from Light to Moderate Throttle

    I have a 2009 XC70 3.2L with 332,000 km. Changing the fuel rail pressure sensor resolve an engine hesitation problem that I have been experiencing for the past year. The engine would hesitate when increasing the from light to moderate loads at speeds around 40-60 kph or 110-120 kph. Checked engine and transmission codes with my Autel MD902 and no codes found. I searched internet and it seemed to point towards the transmission solenoid valves. Changed oil and still same problem. Check transmission with VIDA 201A and shifting was good. I thought it might be a coil as I finally got a code on No6 coil. Changed coil and still hesitation. Finally after a year, fuel rail pressure codes P0190 and P0193 appeared. Purchased a new fuel pressure sensor ($128.00 Cdn) from Volvo and installed in half hour. It has been two weeks and no hesitation. My wife even noted that the car drive much better now.

    The fuel rail pressure sensor provides a signal to the fuel pump controller which adjust the the fuel pump speed to maintain pressure. Older vehicles such as my 2001 V40 used a pressure regulating valve mounted on the fuel rail and a constant speed fuel pump. In the case of my XC70 it would appear that over time the fuel pressure sensor lost calibration and causing the fuel pump to operate at a much lower pressure than indicated. Looking back the hesitation now reminds me of my carburetor days when the accelerator pump would stick and the car would hesitate. Low pressure in the fuel rail could also cause a similar problem of hesitation by slowing fuel flow during throttle changes. This is what I believed caused my issue. The other end of fuel rail has a port for connecting a mechanical gauge but it requires a special fitting.

    In summary if you have a high mileage XC70 that hesitates during low to moderate speed increase it might be worth checking the fuel rail pressure or just install a new fuel rail pressure sensor.

  2. #2
    Join Date
    Dec 2016
    Location
    NC
    Posts
    9

    Default

    Thank you for the information. I will keep this fix in mind if I start hesitating on my 200,000+ mile 2008 XC70.

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