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Omega Help Area => Omega General Help => Topic started by: harpersimon on 13 December 2010, 14:26:54

Title: Runs rough with high throttle demand
Post by: harpersimon on 13 December 2010, 14:26:54
Hello
when I drive around 'normally' cruising about, car is faultless - smooth etc. IF I demand throttle (jam the pedal down) for a swift overtake or junction pull away etc - I get juddery performance, an almost mis-firing display, until the engine really gets going to high revs.
Doesn't matter if cold or hot particularly, no codes showing, might benefit from a set of plugs but thats about it..
Title: Re: Runs rough with high throttle demand
Post by: Kevin Wood on 13 December 2010, 14:29:01
Could well be something weak in the ignition area so if it's due a change of plugs try that first, checking for any oil in the plug wells.

Failing that - clogged fuel filter perhaps? :-/

Kevin
Title: Re: Runs rough with high throttle demand
Post by: harpersimon on 13 December 2010, 15:14:52
mmm thing is wouldn't a dodgy plug or two manifest itself in more ways, i.e. general rough running at all rev ranges?
its only on pick up from cruising about, and goes away - almost like it clears its throat once it gets on full chat. Not so bad in S mode, but then the revs are already up a tadge more than non sport
Had the cambelt done a while back and having enquired I was told that it may take a while to sort itself out ECU wise - - was thinking cambelt change related issue but can't think what would affect it, since daily running is perfect, MPG is same as ever, all is well unless booting is.. sometimes
where is the fuel filter? Easy job?
(last one of those I did was on an A8 in a 'cover you in fuel' position half way under the car :-)
Title: Re: Runs rough with high throttle demand
Post by: 2woody on 13 December 2010, 15:16:57
something amiss in the ignition will manifest itself under conditions of the highest spark demand - which is high revs/high load and low revs/high load
Title: Re: Runs rough with high throttle demand
Post by: Kevin Wood on 13 December 2010, 15:20:01
The highest demands on the ignition system occur where the volumetric efficiency, and hence compression pressure, is highest, so around the torque peak (mid RPM and full throttle). As the ignition system degrades, this is where it'll start to show symptoms first.

Thinking about it, if it pulls cleanly above this speed, it's less likely to be the fuel filter but if there is no history of this having been changed it's probably just as well to do so. It's located underneath the car, just ahead of the fuel tank.

Kevin
Title: Re: Runs rough with high throttle demand
Post by: henryd on 13 December 2010, 15:31:14
my mig did exact same thing when I got it,ran fine until full power was required.Mine was oil in plug wells which when sorted cured the problem
Title: Re: Runs rough with high throttle demand
Post by: harpersimon on 13 December 2010, 15:38:24
Quote
something amiss in the ignition will manifest itself under conditions of the highest spark demand - which is high revs/high load and low revs/high load

thanks chaps, I will start checking things..
High revs there doesn't appear to be an issue - pulls fine when on song, just when cruising at 40, and then pressing the throttle enthusiastically i get stutter.. stutter.. nothng.. nothing.. then whoosh.  (scientific description)
its like it wants to go.. then does. I'll go for the easy fuel filter first and see whats what
Title: Re: Runs rough with high throttle demand
Post by: freecall666 on 13 December 2010, 16:05:14
when was the plugs last changed?
Title: Re: Runs rough with high throttle demand
Post by: Omegatoy on 13 December 2010, 17:40:08
Hmm two questions to the more knowledgeable amongst the petrol heads, could it be the sludgepumpgearbox trying to sort itself out? or possible its the tc?

edit vacuum pipe off or split to the multi rams?
Title: Re: Runs rough with high throttle demand
Post by: freecall666 on 13 December 2010, 18:26:51
could it be the speed sensor, if you do 40 in 3rd dose it do the same??
Title: Re: Runs rough with high throttle demand
Post by: Varche on 13 December 2010, 18:46:41
Have you had a look under the bonnet in the dark for tracking on the plug leads?

My money is on a Dis pack problem.
Title: Re: Runs rough with high throttle demand
Post by: harpersimon on 15 December 2010, 16:46:57
wow lots of things here!
not looked in the Dark for tracking plugs
no idea when the plugs were changed, been meaning to but being a V6 not the simplest 5 minute job
Fine at 40mph, no issue unless I stamp on the throttle
Need to check the vac pipes, but all seem sound to me, the 4 across the back of the plenum that is

Pugs and filter next weekend I hope.. then see where we are
Title: Re: Runs rough with high throttle demand
Post by: msb1973 on 15 December 2010, 20:59:43
sounds very similar to the misfire on my car fine on light/part throttle, judders and misses like a tw*t on full load :-?