Hi everyone,

We've gotten back from our ninth trip to southern Italy in the Omega, but this time she developed a severe miss just south of Naples. I checked her over and found a little mayo on the overflow cap and some drops of oil in the water, but the oil was ok and temperature ran fine.

I kept an eye on everything and running on five cylinders (occasionally with severe knock) we managed to get back to the UK.

Since we got back, the miss has almost completely gone away but there is quite a lot of oil in the cooling system now.

I have dropped it with my mechanic who thinks the oil cooler has failed and that the miss is something else.

So now I'm trying to work out what caused the severe misfiring and knocking!

Actually for some time now, when I start the car from cold, it soon starts miss firing until it gets so bad that it nearly stalls. As soon as it warms up, it goes away, all of which suggests some sort of ECU or sensor problem.

It's worth mentioning that the engine light has been on for some time due to the lambda sensors. I assumed this is because of the well known cat issue with V6 engines, but now I wonder? Also, it has an LPG conversion.

Before I start changing random sensors I would appreciate some input.

Thanks in advance.

Dominic

You need to do a pedel test to see what codes are stored...

http://www.omegaowners.com/forum/YaBB.pl?num=1189022687

I suspect the fault with you lambdas has been keeping the EML on and possibly masking another fault.

My best guess would be cam cover seals gone, allowing oil into the plug wells and causing the misfire.

Expect codes 0300 through to 0306.  :y

It's not the lambda sensors themselves, but the pre cats that are at fault. Yes it's common, but knowing that, it's really wise to perform regular pedal tricks to confirm that's all that's wrong.

As Twiglet says, pedal trick to confirm the codes. In addition expect your pre cat codes 0420/0430.

LPG will seek out the slightest miss fire. Luckily these ecu's shut down the injectors on I missing cylinder, or more serious damage would result.

If miss is confirmed, new plugs are cheapest from vx, coil pacs from vx parts warehouse are competitive. And check the windscreen seal to scuttle is fitted correctly go keep water out of the engine bay.

How many miles has it done in total?

Thanks for the Pedal Trick tip. I'm going to see the car today, will mention oil in the plug wells to the mech.

The car has about 220K miles now. Actually I had the plugs changed when the misfire first started just recently and the coilpacks are about 40K/50K old. How can one diagnose the coil packs?

I went past the mech yesterday. He showed me the leak test they did on the heat exchanger and sure enough it was leaking, albeit very slowly - just a few small bubbles.

I also mentioned the oil-in-the-plug-well problem.

Apparently no one had the heat exchanger in stock so won't have the car back until Friday.

And first prize goes to the "oil in the plug wells" answer.

Collected the car today, he said the plug wells were full of oil so he cleaned them out and changed the rocker gaskets.

Still some drops of oil in the cooling system, I'll take it back to him next week to have that cleaned.

Thanks for all your help.

I have another question about the engine being hard to start on LPG, but I'll post that separately.