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Author Topic: 2.5 V6 Petrol - Engine was velvet, gone lumpy  (Read 583 times)

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2am Omega

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2.5 V6 Petrol - Engine was velvet, gone lumpy
« on: 05 January 2009, 01:27:08 »

97 R plate Omega Elite 2.5 V6 Petrol engine ran as smooth as velvet .. now suddenly lumpy with reduced power and petrol consumption almost doubled. Possibly not firing on all 6 cylinders? Was fine until MOT .. coincidence? Suggestions welcome please on possible causes to explore.
« Last Edit: 05 January 2009, 01:41:26 by 2am »
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Elite Pete

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #1 on: 05 January 2009, 08:28:49 »

I would start with the paperclip test and see if there are any codes stored
http://www.omegaowners.com/forum/YaBB.pl?num=1189022687

Check plug wells for oil ;)
« Last Edit: 05 January 2009, 08:30:18 by Elite_Pete »
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2am Omega

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #2 on: 05 January 2009, 16:33:19 »

Thanks Pete .. Paperclip Test suggests no fault. It flashed (3 repeats each) of 12 then 31 .. then repeats same cycle. This seems normal for 2.5 V6 with ignition on but no revs. Tried Paperclip Test again with engine running .. it just flashes 12 repeatedly, suggesting no fault. So now to Plan B .. any other suggestions please?

I wondered about possibility of water in fuel .. I did fill to brim with half a tank after leaving MOT test station .. but (big supermarket) garage says not aware of any other similar incidents. Spark plug or connector? I have had this Omega Elite for over 3 years .. always been smooth and sweet.
« Last Edit: 05 January 2009, 17:07:35 by 2am »
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Elite Pete

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #3 on: 05 January 2009, 16:46:19 »

No codes might suggest dis pack, plug leads or plugs. Did you check the plug wells for oil?
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2am Omega

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #4 on: 05 January 2009, 17:41:41 »

Inspected depression wells around plugs on top of cylinder head .. no sign of any oil.

Pete, you said "No codes might suggest dis pack, plug leads or plugs."  Please explain what is "dis pack".

Please note I slightly modified my previous post after the time of your reply.

Any other suggestions please?
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TheBoy

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #5 on: 05 January 2009, 18:02:43 »

DIS is the coil pack behind 2/4/6 pack that provides the HT to spark plugs. Does a similar job to coil and dizzy on older motors.

Misfires with no codes stored tend to be HT related (plugs/leads/DIS).

You say its lumpy? Lumpy at tickover? If so, look for air or vac leaks.
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2am Omega

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #6 on: 05 January 2009, 18:41:49 »

Thanks TheBoy - looks like the HT system needs checking. Plugs seem pretty inaccessible, especially on nearside. Is it feasible for a novice to remove and check plugs and leads, or should I leave it to a skilled mechanic?

Lumpy engine is at all revs (up to about 2800 .. no need to exceed that) including tickover. Example .. warmed up tickover at 500-600 revs is lumpy, causing dashboard lights to flicker slightly.

Fuel consumption has suddenly doubled .. only 12 to 18 mpg shown on computer now.

This may be irrelevant but I will mention that exhaust rear box baffles are rattling loose inside and some wadding strands have blown out of the tailpipe. There is good exhaust pressure from tailpipe. It was checked yesterday at Kwik-Fit. They said leave it since overall exhaust system is sound. They thought the lumpiness was caused by "something in the engine compartment".

Remember the car just passed its MOT and the lumpy engine problem emerged as I drove away from the test station. Sabotage he wonders .. after grumbling about overcharging for brakes work??

Any other suggestions please?
« Last Edit: 05 January 2009, 18:46:44 by 2am »
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MarkG

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #7 on: 05 January 2009, 19:11:23 »

I'd suspect dispack. Get the scuttle off and check Heater Bypass Valve has not been leaking water all over it and that it still looks OK. New Bosch Dis Pack about 80. It is a bit of a bugger to get at though.

If it's not that, then try new plug leads and while you are at it, new plugs. No need to use genuine vauxhall leads which are over 200 for the set. Mine were about 40.  It is all quite do-able at home. Just take your time
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Entwood

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #8 on: 05 January 2009, 19:33:50 »

My old 2.5 went all weird and lumpy, many checks didn't find a fault .. but wnhen I mentioned the "horse hair" out of the exhaust all the experts here said back box breaking down so change it .... I did and all the problems went away !!

Consensus was that even though the pressure felt good, the flow through the system was "wrong" and the ECU was "correcting" for this so causing the poor running ... wonder if thats your problem as you have "bits" escaping from your exhaust ??
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2am Omega

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #9 on: 05 January 2009, 20:45:57 »

Thanks for the guidance, guys. First I think I will change the exhaust rear box, which is approaching the end of its life and may provide the solution.

Then check the HT system and DIS Pack ..  should this be by trial and error, starting with plugs and connections, or some type of Diagnostics to test leads and DIS Pack?

I'm sure I could find another Paperclip if necessary  ;)
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Fuse 19

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #10 on: 05 January 2009, 20:49:18 »

It wont be the exhaust......if it was then it would tick over fine on idle where very little exhaust gases are produced  :y

DIS pack is the favourite given the symptoms
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eddie

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #11 on: 05 January 2009, 21:59:51 »

Is there a smell of unburnt fuel at all--Everything you mention plus a fuel smell, ended up being the DIS pack in my case.

Pain in the butt to do but possible by an amatuer with a little knowledge and help.  Wouldn't like to try in this weather though!
Take a look at the excellent how to's on this forum.

eddie
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2am Omega

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Re: 2.5 V6 Petrol - Engine was velvet, gone lumpy
« Reply #12 on: 05 January 2009, 22:26:43 »

I will check for unburned fuel emitting from the exhaust tailpipe.. by smell, rather than using a lighted match !!

Thanks Marks, Eddie and everyone else .. it seems the concensus points to the DIS Pack.

Diagnostics .. Can the DIS Pack be tested? or is it necessary to replace it before you know if it is the culprit?

Is it worth trying to pick up a salvaged unit at a scrap yard? Costly repairs are concerning on these wonderful cars which, sadly, hold little open market value by age 12 and after trekking 130,000 miles !!

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