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Thread: Light misfire and poor fuel consumption on 2.8 ACK engine

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  1. Light misfire and poor fuel consumption on 2.8 ACK engine 
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    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 enigine revs flew up when I touched the accelerator, tried to take off gently, engine stalls with a smell of petrol. there's a light misfire at low revs when pulling 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 200cpi cats and a free flow exhaust, otherwise standard.

    VAG-COM showed 2 errors, maximum fuelling limits exceeded, and no positive feed to either lambda sensor. As a test I replaced the lambda 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 lambda sensor cured some of the misfire.

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

    I'm not certain that 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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  2. Re: Light misfire and poor fuel consumption on 2.8 ACK engine 
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    I had a very uncommon problem on my 1.6 A4, the ht lead for the number 1 cylinder had snapped in the rubber boot were it connected to the coil.The connection was maintained as it was held by the rubber, but the movement of the engine when taking up power would cause it to wobble and miss fire.Took me about 5 hours to fix all in all, as once I eventualy got the coil off it was a nightmare getting to the brass ring that holds the lead onto the unit out. Faults like this don't show up on the engine management system, as (as far as Im aware) no sensors that check the output or sparking of HT leads. Best way to test is check the spark from each lead using a spark plug tester,it goes between the lead and plug and is a semi transparent plastic so you can see the spark strength. It will be clearly visable to see with is'nt firing properly, and then just work backwards from there. Could just be a duff spark plug, if its not firing properly youll get unburnt fuel being spat out the exhaust, this will eat your fuel consumption massivly! Hope it helps! Give me a shout if you need any more help! And let me know how you get on!
    Audi A4 B5 1.6 -1998 <~~~ GONE
    Audi A4 B7 2.0 - 2005<~~~ GONE
    Audi A4 B5 1.8 T 1996 <~~~Here for now

     
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  3. Re: Light misfire and poor fuel consumption on 2.8 ACK engine 
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    That's really helpful, thanks. Will add it to my list of things to check next week. The car's had one replacement lead in the past. The other thing I'm looking at now is the inlet air temperature sensor, on top of the intake plenum. have done a visual on this and the MAF hot wires, which showed up nothing. Hot wires were black so cleaned them in alcohol. problem is, not knowing what readings I should get across the pins to identify an electrical fault.

    ajs
     
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  4. Re: Light misfire and poor fuel consumption on 2.8 ACK engine 
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    Have now performed a MAF test on VAG - reading max 160, so that's fine. Air intake temperature sensor had errored, so got a new one on order. It's Audi only for this model, as it's not a dual sender. 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. 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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  5. Re: Light misfire and poor fuel consumption on 2.8 ACK engine 
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    Im sure its not knacked,just needs nursing better,new leads will probably do it if theyre showing signs of exessive resistance. Try taking th eplugs out and cleaning them aswe,if nessasary replace them.All the small things a make a big difference.
    Audi A4 B5 1.6 -1998 <~~~ GONE
    Audi A4 B7 2.0 - 2005<~~~ GONE
    Audi A4 B5 1.8 T 1996 <~~~Here for now

     
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