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Light misfire and poor fuel consumption on 2.8 ACK engine

Discussion in 'A4/S4 forum(B5 Chassis)' started by ajsphead, Feb 14, 2008.

  1. ajsphead
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    ajsphead New Member

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    [Feb 14, 2008]
    Can anyone help out with a fairly complex problem I've got with my 97 2.8.

    It had 3 problems, the first was on initial cold start, the engine revs flew up when I touched the accelerator, tried to take off gently, engine stalled with a strong smell of petrol. There's a light misfire at low revs when pulling gently in a high gear, and recently, the fuel consumption has dropped from 30mpg, to nearer 20. It's running a free flow replacement panel air filter, new 200 cpi cats and a free flow exhaust, otherwise standard.

    VAG-COM showed 2 errors, maximum fuelling limits exceeded, and no live feed to either lambda sensor. As a test, I replaced the sensor on bank 2, and with it the other one came back to life, and both are switching within operating limits. I've had it gas tested and it's passing all tests well within limits. Changing the sensor cured some of the misfire, but nothing else.

    I replaced the coolant temperature sensor, which has virtually cured the cold start problem, but should it cold idle at 1150? The accelerator when cold, is still more sensitive, but the misfire has eased a bit more.

    I'm not certain the air mass meter throws an error on this ECU, but I think the coil packs do, and they are fine.

    What values should I get across the pins of the air mass meter ? and what other bits can I check ?

    At no time has the engine management warning light come on, and all the wiring and fuses are fine.
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  3. Mothy69
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    Mothy69 3rd Gear

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    [Feb 14, 2008]
    mine can do on occasions, but only v briefly before settling to just below 1000..
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  4. ajsphead
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    ajsphead New Member

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    [Feb 14, 2008]
    It sits at 1150 for about a minute, and if you give the throttle a blip, it returns to 1150 quite slowly. Once it's warm, then it's fine. this is after the new coolant temp. sensor.

    Anthony
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  5. Mothy69
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    Mothy69 3rd Gear

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    [Feb 15, 2008]
    sorry i cant help with your more major issues - but, had a look at mine last night & it does what you've described.

    out of interest which 2.8 is yours? either the 192 or 172 or something similar.

    Hopefully someone more technical than me can help with your other problems.. good luck
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  6. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Feb 15, 2008]
    The MAF will cause poor running and economy, as you have VAG go log block 2, do a 3rd gear pull from say 2k revs till the red line and that should give a log of air drwn/measured. I would expect it to be around 150m/gs ish depending on the model you have
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  7. ajsphead
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    ajsphead New Member

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    [Feb 16, 2008]
    hi Mothy

    All the a4's in the uk were 30v's, as far as I know, so it's 193. I was reading a posting on the A6 forum, from someone who had the same problem with an a6. Am just off to check the dual temperature sensor this morning. this also doesn't throw an error on VAG-COM.

    ajs
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  8. ajsphead
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    ajsphead New Member

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    [Feb 16, 2008]
    Thanks Byzan

    If/when the neighbours finally go out I'll run a check as you suggest. The free flow exhaust has just got very noisy in the last day or so, so it's currently audible from about 1/2 mile away according to my wife.

    ajs
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  9. ajsphead
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    ajsphead New Member

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    [Feb 23, 2008]
    Have now performed a MAF test on VAG - reading max just over 160 m/gs, so that's fine. Air intake temperature sensor had errored, exceeding max temp. limit, so got a new one on order. It's Audi only for this model,as it's not a dual sender £ 48, usual rip off. Have now tested the plug leads too. Should be 5K Ohms. I have 3 at 5.1, all on bank 2,1 @ 4.7, 1 @ 5.3, and 1 @ 5.8 on bank 1. Have now ordered a new set of leads. Not great to be knackered at 55K.

    Reckon these things will solve it. Don't know what else it could be if not, as VAG is otherwise clear. Will probably buy a 1 litre Polo off ebay and just use the Audi for club meetings and events if I can't sort it.
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  10. ajsphead
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    ajsphead New Member

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    [Feb 23, 2008]
    Hve also bolted the exhaust back together. It actually sounded quite tasty with only 1 box and a side exit pipe.
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