Misfiring Omega - unable to diagnose

Got a misfiring '99 Vauxhall Omega 2.5.

The engine was smooth and stable until it was started last Tuesday when it suddenly started misfiring. At idle, it seemed to be ticking over on 5 cylinders. Being driven, it would hold-back, then surge repreatedly under throttle.

I took half the plugs out, and found the front o/s plug (whichever cylinder number that is) wet with petrol. I checked the lead against the block and there was no spark. I swapped the lead with one from another Omega, no change.

Dropped it into the garage, and they changed the plugs and leads as a matter of course. They connected the car up to their analyser, but the computer wasn't reporting anything wrong (no engine management lights on the dash either). They've done a compression test on the car, and all 6 cylinders are fine. They checked all the sensors with an ohmmeter and everything 'seems' ok.

The only thing they could suggest was the coil-pack, or DIS (which I'd thought might be the problem when I was getting no spark off the lead). They're going to change it over, but thought I'd throw t open to the group as well. Anyone come across anything similar? Would DIS seem to be the likely fault? Any other suggestions if it doesn't cure it?

I vaguely remember reading something about DIS firing in pairs? 1&5, 2&4,

3&6 or something like that. Wouldn't that suggest a faulty DIS would cause to cylinders to miss?

I'll post a follow-up, hopefully tomorrow, as long as the new DIS has arrived.

Thanks, Paul

Reply to
Paul
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As you have ruled out the plugs and especially the leads, and as the fault came on suddenly, i'd put money on a faulty coil pack- having shorted internally to earth. (hence number 5's companion plug is still firing ok)

Tim..

Reply to
Tim..

No news from the garage as yet. Still fitting the new DIS and won't be ready until tomorrow.

Reasurring that you're thinking along similar lines to me though!

Another update tomorrow...

Cheers Paul

Reply to
Paul

Got the car back from the garage. The new DIS has cured the problem.

As part of my "identifying the problem cylinder" process, I take the lead off each cylinder in turn, while the engine is running to listen for any change in the engine revs, and check for a spark against the engine block. In this case it was the DIS at fault, but in any other case, is this test bad for the DIS?

Thanks Paul

Reply to
Paul

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