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lean running problem

Discussion in 'A4/S4 forum(B5 Chassis)' started by dann959, Nov 1, 2004.

  1. dann959
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    dann959 Member

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    [Nov 1, 2004]
    Hi i've been having trouble for about a month and a halve now. I have been getting code 1128 about every 75-80 miles of driving. I clear the clode with my scanner when it comes up. The code is supposedly a long term fuel trim problem (lean condition). The car loses power when before and sometimes while the engine light is on. After i clear it power is usually restored. I step floor the pettle sometimes and the car is just not accelerating like it should be especiallly since it is chipped. My mechanics first step was to replace the fuel filter which was pretty dirty after 63k. It helped but the problem is still occuring. This all started happening about a month ago after a vacum hose was replaced whether or not that has anything to do with it i dont know.

    I was talking with the mechanic today and he and i agreed that it could be a faulty o2 sensor that hasnt completely died yet, or a bad fuel pressure regulator. The vacume hose that was replaced was replaced with regular air haose instead of the hard plastic that audi uses. But we doubt thats the problem. We still might replace it though. Anyway any ideas on o2 sensors and fuel pressure regulators? He said he might hook up a pressure meter to the fuel system and drive it to see if it holds pressure. Other than that he cant do much more diagnosis off a 1128 code.

    Do you think I need an upgraded fuel regulator since the car is chipped? Any ideas on what is causing the power loss? I am open to all suggestions.
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  3. dann959
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    dann959 Member

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    [Nov 2, 2004]
    heres an interesting update: when i fueled up today at the gas station i noticed that my power was restored even with the engine light still on. i will see how many miles of driving before the power starts to fade again. what could a full tank of gas have to do with this problem? Or is it just a coincidence?
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  4. simon_golf_tt
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    simon_golf_tt Member

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    [Nov 2, 2004]
    Given the fuel filter has made a difference - I'd check the fuel pump. You can do this with a fuel pressure tester. Assuming you have a 4 bar fpr, the pressure should be 3.5bar at idle and then go up to 4bar+peak boost at peak boost. Fuel pumps can die slowly and therefore not make full pressure. The fpr maintains a constant 4 bar pressure differential between the intake manifold and the fuel rail to give constant injector performance. At idle your engine creates a vacuum of about 0.5bar and that's where the 3.5 comes from.
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  5. dann959
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    dann959 Member

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    [Nov 6, 2004]
    got my MAF cleaned and scraped the k&n with a stock filter still tripping engine light code 1128. ???????
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