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[Jampy]

Hi everyone, I'm new on the forum and hope somebody can help with my current problem.  I drive an Omega 2.0 Auto 1999 on which a new fault has developed in the last 4 months.

When accelerating with a warm engine through the automatic gear changes, a last change up into top gear occurs at about 3000 rpm, when the revs then settle around 2000 with a road speed of 50 mph.  The engine then misfires and becomes jerky, but further acceleration to higher rpm clears away the jerkiness again.  Any drop in speed and revs to about 2000/2500 brings back the jerkiness/misfires, and further reduction below 2000 removes it again.

A test drive from cold was OK with no misfiring, but after a short while and a warmer engine it starts again .  I can also get it to happen if I manually drop the automatic into third and test it around 2000/2500 rpm.

Vauxhall garage reports no codes, DIS is OK, and changed the plugs, and the well around the plugs is bone dry.  They suggest it might be the MAF meter and will do a test swop tomorrow to find if it clears.

If not, they haven't come up so far with any alternatives.  Does anyone recognise these symptoms?  I would be grateful for any help as I need to clear this problem before driving off for any long trips.  

[tmx]

if your hereford located??? i may be able to help....

im assuming your shire folk as you mentioned Polytec Holden

[sonikhead]

hello there i have had the same symptons on my 2.5 auto exactly the same in fact. took it to the garage did a diagnostic and no faults were found. changed the dis pack and hey presto it was cured.

[Jampy]

Thanks TMX for your offer, but I am in Daventry.  Same answer on Rusty Sills  thread.  

If I get no answers beforehand I'll let you know how I get on at the garage tomorrow.

[Jampy]

Thanks Sonikhead.  The garage mechanic claimed the DIS pack is OK.  I have no idea what check he would carry out to say that.  Maybe he didn't give it enough attention and thought he would get away with just changing the plugs!  We'll see what develops.

[Welung666]

Have you read the codes? See the link for the paperclip test in my sig

[tmx]

paperclip it if theres no codes then i would suspect HT Leads/DIS Pack

remove the plugs plug by plug off the dis pack and see if theres any corosion on any of the terminals

[Jampy]

Thanks Welung666 and tdx.  Garage said no faults.  Do you think I might find faults nevertheless.  I mean, does it happen?

[tmx]

yeah try a paperclip test wont break your car its perfectly safe!

you may find a code

if it repeats code 12 over and over then you have no problems

[Jampy]

Thanks again tmx.  Just done the paperclip test.  Mine is a 1999 2.0l and the test gave no flashes at all, not even code 12.  Presume 12 is omitted on this model and no flashes therefore indicates no codes recorded?

[deecee]

sounds like heat problem could be leads breaking down under temp ,garage test will not find if only happens under heat/power when car running,hope it helps

[tmx]

Thanks again tmx.  Just done the paperclip test.  Mine is a 1999 2.0l and the test gave no flashes at all, not even code 12.  Presume 12 is omitted on this model and no flashes therefore indicates no codes recorded?

you need the engine running on 2litres i believe

[Jampy]

Thanks again to tmx and ceedee.

Paperclip test says it will not work if the engine is running on the 2.0l.  It also says it will go straight into fault codes, without signalling 12 on later Omegas, but would that include a 1999 model, I wonder?

At the GM main dealer yesterday they swopped the MAF with absolutely no improvement.  Now they are backtracking and think it might be the DIS pack after dismissing it at the start.  They also feel, like deecee suggests, that it might be the ignition leads, saying two of them show a high resistance at raised temperature.

With a quotation of £170 to replace both, I plan to walk away and do it myself, since the leads cost £25 delivered and the DIS pack £35 delivered. I'll do the leads first, since 10 years on the initial set signals a change anyway, and if the fault continues I will replace the DIS pack, which looks simple on the 2.0l.

[Jampy]

Just done a multimeter test on the leads.  One of them is open-circuit, giving no reading.  Must be sparking across internally!!  Could that cause the problem at selective RPM?  My garage man claimed to have measured two leads having higher resistance when hot.  How come he missed the open circuit one?  I don't think he even checked them!!

[Jampy]

Just fitted new Bosch ignition leads (£25) and done a test drive.  Problem solved!  It was the broken lead. Now, the car runs at 60 mph at 2000 RPM compared with 50 mph at 2000 RPM previously, and without any jerkiness/misfires.