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Missfire Diagnosis - Running out of options HELP......

Discussion in 'Audi S4/A4/A4 Cab (B7 Chassis)' started by Scott.T, Nov 11, 2012.

  1. Scott.T
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    Scott.T Member

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    I have a 2.0TFSi Quattro that has a mild missfire between 1700rpm and 2500rpm. Although it is less noticable at above 2200rpm and never noticable above 2500rpm.

    It's only on very light throttle and any deflection in throttle angle causes the missfire to stop.
    25% throttle or full throttle pulls, through from 1200rpm, are smooth with no cough's or misses at all.

    I am however running out of options......so far I have fitted/done the following :

    New DV (old one had a split diaphram)
    New Coil Packs
    New Plugs
    New MAF
    New PCV
    New HPFP Cam Follower (old one was pretty much OK)
    No sign of cam wear when changing HPFP follower
    Diagnostics report 700-720psi fuel rail pressure at Idle and upto around 1500+psi at other times (monitored before the HPFP follower changed)

    Throttle pedal was removed and stripped/cleaned with contact cleaner. There is some adjustment on the pedal so this was set to the max amount of adjustment available. It made a noticable difference to performance, as it clearly wasn't get full throttle. However, the missfire was still present at shallow throttle angles and at the same rpm as before. The throttle was then reset to the original position and full throttle was regained, and missfire was no different.


    Fuelling check using Innovate LC-1 Lambda in exhaust shows nice steady 14.7AFR at idle and cruise and up as rich as 11.6AFR at WOT / high Rpm.

    During cruise there is no deflection in AFR (logged using Innovate LogWorks) noticable during missfire events
    Missfire is still present with Lambda removed, although ECU default fuelling is a touch leaner, being between 14.7AFR and 15AFR.

    Monitoring boost/vacum and the missfire always occurs at -15 To -20 in/hg vacum. Outside of this range it appears OK.

    Boost appears to be about 11psi dropping to about 5psi at high rpm, but I want to log this again with an analogue gauge to confirm.

    Car has covered 89,000 miles with Full Audi Service history and is very clean and well looked after by it's previous owners (I've only had it 3 weeks). I was suprised how good the HPFP follower was after seeing some on here and other interweb images.

    Any help would be much appreciated......
    Last edited: Nov 11, 2012
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  2. Rick @ Unicorn Motor Dev.
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    Rick @ Unicorn Motor Dev. Site Sponsor Site Sponsor

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    Have you inspected the actual cams for wear?

    Do you have VCDS to log?

    If so, go to advanced measuring blocks and click the turbo button. Log MAF, requested load, actual load, ignition angle, RPM, requested rail pressure, actual rail pressure, exhaust gas temp. Send them to remapping@unicornmotordevelopments.com

    Rick
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  3. Scott.T
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    Scott.T Member

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    Unfortunatley I havn't got VCDS only a generic OBD tool at the moment......that's another £250 on a car I can't decide whether it's a keeper the way things are going.
    I went for an Audi as I wanted German quality and reliability, it seems to be letting me down at the moment.
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  4. Scott.T
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    Scott.T Member

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    Just realised my ECUEdit application I use on the Subaru for logging and flashing also has OBD aswell as Subaru Select Monitor and Mitsi Evo logging, so I will see what I can get from that.

    Cheers
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  5. Scott.T
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    Scott.T Member

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    Are they easy to inspect ? Rocker cover off or more then that ?
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  6. Scott.T
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    Scott.T Member

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    OK, might be getting somewhere here.......

    Since owning the car and noticed on the 45 mile trip from collecting it, the temperature gauge seemed to fluctuate from aprox 65 DegC to 90 DegC. Fitting a new Coolant Temp sensor (Grey 2 pin), didn't cure the problem, so assumed it was either normal or thermostat related.

    I thought I had moments where the car started to behave/not missfire and this always seemed to be when the Temp gauge was reading 90 DegC. Due to the nature of the condition inducing the missfire I always dissmissed this as just a fluke or me being unable to re-create the condition.

    Tonight whilst logging some parameters on a generic OBD (Torque Pro) I pulled over for 2 or 3 mins to make adjustment to the logging as the induced missfire was happening, but what I was logging was stable and un-effected.

    After pulling away I could not reproduce the missfire but once again noticed the Temp gauge was reading 90 DegC.
    Once the temperature started to drop the missfire was quite easily reproduced.
    I then turned the car around and drove up the road quite easily creating the missfire.

    I returned back to my turning point and sat for 3 or 4 minutes waiting for the Temp Gauge to hit 90 DegC.
    Driving the exact same road I could not reproduce the missfire all the while the temp gauge read 90DegC.

    As soon as this started to drop towards it's usual point (90% of the time it's around 70 DegC), the missfire returned.

    So I assume there is a fault with the thermostat hence why it is not regulating the temperature well.

    BUT is there another engine temperature sensor that could also be at fault that controls fuelling / timing based on the engine temperture.
    Could it be running cld start fueling and timing based on ECT (Engine Coolant Temperature) ?

    I know some vehicles have 2 engine temp sensors one for the dash/gauge and one (probably more acurate) for ECU closed loop control.
    I can't imagine the ECU uses the 2-pin for ECU control (mine is a grey 2 pin and not the green 4 pin that I thought might be fitted), due to it's very basic nature.

    Engine is a BGB 1st Registered Jan 2005.
    Last edited: Nov 12, 2012
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  7. Scott.T
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    Scott.T Member

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    Just been out for another drive over lunch to see the effects of hot/cold running.
    All the time I was logging coolant temperatures via OBD (Torque Pro).

    Normal driving and it's sitting around 68-71 DegC and the missfire is quite easy to reproduce at light throttle 2000rpm. Easiest done on a flat/level straight stetch of road.

    Let the car idle for a while, although quicker to sit stationary but bring revs up to 1500rpm and watch the dash gauge climb and the coolant OBD come up to 85DegC+ (I took it as far as 89DegC). Gauge in car actually reads nearly 90DegC when Coolant OBD reports about 82DegC.

    Off for a drive at 85-88DegC, same stretch of road, same scenario and I cannot reproduce the missfire.

    As the temperature drop down to below 80 DegC and heads ever closer to it's normal of 70 DegC the missfire get's easier and easier to reproduce.

    Needless to say during this excursion lunchtime, it included a stop at GSF to order a new thermostat.

    If the cold running enrichment is kicking in all the time due to it running at 70Deg (20Deg below the norm) in the ECU map, I'm wondering if there is a better later revision of firmware. Mine is an early 2.0TFSi, although it does have full Audi dealer history so I would hope any revisions would of been squirted in.
    If I could get into this ECU as easy as I can my Subaru I could quite easily modify the enrichement maps to see if it has an effect. But alas............
    Last edited: Nov 13, 2012
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  8. Marrow
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    Marrow Member

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    Mine does some thing similar although mine is revo stage 1 mapped temperature seems to affect the severity of mine? I have changed all the same things due to failures and still no improvement but I have to say it's that mild it's hardly detectable Audi specialist I use said they couldn't feel it and logs were spot on? And they know their stuff!
    Owned the car 4 years and it's nearly always done it just put it up for sale will be a little sad to see it go the car has been good to me but I want some thing smaller and faster!
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  9. Marrow
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    Are you using torque app on your phone?
    I use this and my coolant temp is usually 80c unless stationary then it raises a little?
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  10. Scott.T
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    Scott.T Member

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    Yeh torque pro, and it seems to pretty much match the car's gauge except then torque reads 82-85 the car gauge is about the thickness of the needle below 90.
    Apparently normal operating temp is around 87 DegC which reads 90 on the car gauge.

    Sounds like we may have the same issue as you can certainly feel the missfire when running 68-72DegC as it gets into the low 80's its very very subtle almost to the point you think you are getting paranoid. High 80's and I really can't detect anything.

    I will be Seafoaming at the weekend too, so clearing some carbon deposits out should help a little too.
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  11. Marrow
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    How do you sea foam mate any links to guides?
    Strange how temps are different and u seem to be getting fluctuation? Mine has always been bad until fully warmed up then misfire seems to usually clear.
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  12. Scott.T
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    Scott.T Member

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    2010 MK6 GTI Seafoam intake cleaning - YouTube
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  13. Rick @ Unicorn Motor Dev.
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    Rick @ Unicorn Motor Dev. Site Sponsor Site Sponsor

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    The dash temp gauge is a little miss leading. From around 80 to around 100 it will read dead on 90C. This seems to be a German thing. These engines so suffer a lot from thermostats failing, infact my own run around A3 TFSI isn't getting up to temperature at the moment. As you have seen, there you can get the true reading from the ECU.

    Rick
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  14. Scott.T
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    Scott.T Member

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    Well changed the Thermostat on Friday, took about 1Hr 30Mins from start to topping the coolant back up.
    A bit fiddly with those damn hose clips and the location of it, but the tip it to try not to take the hose clips off over the hose but go the otherway and just let them hang on the hard pipe once released.
    I also left the short hose that connects between the thermostat and the hard pipe on the thermostat and removed it on the hardpipe end. Then swapped the hose over to the new thermostat before refitting.

    With regard to the missfire. Although this hasn't solved the problem 100%, the missfire isn't present once the car it up close to and running at normal temp (90 DegC on the gauge).

    Whilst on the warm-up period it still has the occasional missfire between 1700rpm and 2200rpm. But it's so much nicer to drive now.

    The problem must be related to a sensor not liking cold running, so will probably try the crank or cam sensors next. But not so much of a rush now as it's 99% solved :):)
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  15. GarJE
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    GarJE Member

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    Only way to properly clean the valves is to pull the inlet manifold off and pick the dirt off.
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